Merge pull request #1172 from quantified-uncertainty/error-locations

Error locations and stacktraces

packages/components/src/components/Alert.tsx

@@ -30,7 +30,7 @@ export const Alert: React.FC<{
           className={clsx("h-5 w-5 flex-shrink-0", iconColor)}
           aria-hidden="true"
         />
-        <div className="ml-3">
+        <div className="ml-3 grow">
           <header className={clsx("text-sm font-medium", headingColor)}>
             {heading}
           </header>

packages/components/src/components/CodeEditor.tsx

@@ -5,6 +5,8 @@ import AceEditor from "react-ace";
 import "ace-builds/src-noconflict/mode-golang";
 import "ace-builds/src-noconflict/theme-github";
 
+import { SqLocation } from "@quri/squiggle-lang";
+
 interface CodeEditorProps {
   value: string;
   onChange: (value: string) => void;
@@ -13,15 +15,17 @@ interface CodeEditorProps {
   width?: number;
   height: number;
   showGutter?: boolean;
+  errorLocations?: SqLocation[];
 }
 
 export const CodeEditor: FC<CodeEditorProps> = ({
   value,
   onChange,
   onSubmit,
+  height,
   oneLine = false,
   showGutter = false,
-  height,
+  errorLocations = [],
 }) => {
   const lineCount = value.split("\n").length;
   const id = useMemo(() => _.uniqueId(), []);
@@ -30,8 +34,11 @@ export const CodeEditor: FC<CodeEditorProps> = ({
   const onSubmitRef = useRef<typeof onSubmit | null>(null);
   onSubmitRef.current = onSubmit;
 
+  const editorEl = useRef<AceEditor | null>(null);
+
   return (
     <AceEditor
+      ref={editorEl}
       value={value}
       mode="golang"
       theme="github"
@@ -59,6 +66,14 @@ export const CodeEditor: FC<CodeEditorProps> = ({
           exec: () => onSubmitRef.current?.(),
         },
       ]}
+      markers={errorLocations?.map((location) => ({
+        startRow: location.start.line - 1,
+        startCol: location.start.column - 1,
+        endRow: location.end.line - 1,
+        endCol: location.end.column - 1,
+        className: "ace-error-marker",
+        type: "text",
+      }))}
     />
   );
 };

packages/components/src/components/FunctionChart.tsx

@@ -1,9 +1,15 @@
 import * as React from "react";
-import { SqLambda, environment, SqValueTag } from "@quri/squiggle-lang";
+import {
+  SqLambda,
+  environment,
+  SqValueTag,
+  SqError,
+} from "@quri/squiggle-lang";
 import { FunctionChart1Dist } from "./FunctionChart1Dist";
 import { FunctionChart1Number } from "./FunctionChart1Number";
 import { DistributionPlottingSettings } from "./DistributionChart";
-import { ErrorAlert, MessageAlert } from "./Alert";
+import { MessageAlert } from "./Alert";
+import { SquiggleErrorAlert } from "./SquiggleErrorAlert";
 
 export type FunctionChartSettings = {
   start: number;
@@ -19,6 +25,25 @@ interface FunctionChartProps {
   height: number;
 }
 
+const FunctionCallErrorAlert = ({ error }: { error: SqError }) => {
+  const [expanded, setExpanded] = React.useState(false);
+  if (expanded) {
+  }
+  return (
+    <MessageAlert heading="Function Display Failed">
+      <div className="space-y-2">
+        <span
+          className="underline decoration-dashed cursor-pointer"
+          onClick={() => setExpanded(!expanded)}
+        >
+          {expanded ? "Hide" : "Show"} error details
+        </span>
+        {expanded ? <SquiggleErrorAlert error={error} /> : null}
+      </div>
+    </MessageAlert>
+  );
+};
+
 export const FunctionChart: React.FC<FunctionChartProps> = ({
   fn,
   chartSettings,
@@ -26,7 +51,8 @@ export const FunctionChart: React.FC<FunctionChartProps> = ({
   distributionPlotSettings,
   height,
 }) => {
-  if (fn.parameters.length > 1) {
+  console.log(fn.parameters().length);
+  if (fn.parameters().length !== 1) {
     return (
       <MessageAlert heading="Function Display Not Supported">
         Only functions with one parameter are displayed.
@@ -47,9 +73,7 @@ export const FunctionChart: React.FC<FunctionChartProps> = ({
   const validResult = getValidResult();
 
   if (validResult.tag === "Error") {
-    return (
+    return <FunctionCallErrorAlert error={validResult.value} />;
-      <ErrorAlert heading="Error">{validResult.value.toString()}</ErrorAlert>
-    );
   }
 
   switch (validResult.value.tag) {

packages/components/src/components/SquiggleChart.tsx

@@ -1,14 +1,9 @@
 import * as React from "react";
-import {
+import { SqValue, environment, SqProject } from "@quri/squiggle-lang";
-  SqValue,
-  environment,
-  resultMap,
-  SqValueTag,
-  SqProject,
-} from "@quri/squiggle-lang";
 import { useSquiggle } from "../lib/hooks";
 import { SquiggleViewer } from "./SquiggleViewer";
 import { JsImports } from "../lib/jsImports";
+import { getValueToRender } from "../lib/utility";
 
 export type SquiggleChartProps = {
   /** The input string for squiggle */
@@ -71,16 +66,11 @@ type ProjectExecutionProps = {
 };
 const defaultOnChange = () => {};
 const defaultImports: JsImports = {};
+const defaultContinues: string[] = [];
 
-export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
+export const splitSquiggleChartSettings = (props: SquiggleChartProps) => {
-  (props: SquiggleChartProps) => {
   const {
-      executionId = 0,
-      onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
-      height = 200,
-      jsImports = defaultImports,
     showSummary = false,
-      width,
     logX = false,
     expY = false,
     diagramStart = 0,
@@ -93,32 +83,8 @@ export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
     title,
     xAxisType = "number",
     distributionChartActions,
-      enableLocalSettings = false,
-      code,
-      continues = [],
   } = props;
 
-    const p = React.useMemo(() => {
-      if (props.project) {
-        return props.project;
-      } else {
-        const p = SqProject.create();
-        if (props.environment) {
-          p.setEnvironment(props.environment);
-        }
-        return p;
-      }
-    }, [props.project, props.environment]);
-
-    const { result, bindings } = useSquiggle({
-      continues,
-      project: p,
-      code,
-      jsImports,
-      onChange,
-      executionId,
-    });
-
   const distributionPlotSettings = {
     showSummary,
     logX,
@@ -138,13 +104,51 @@ export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
     count: diagramCount,
   };
 
-    const resultToRender = resultMap(result, (value) =>
+  return { distributionPlotSettings, chartSettings };
-      value.tag === SqValueTag.Void ? bindings.asValue() : value
+};
-    );
+
+export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
+  (props) => {
+    const { distributionPlotSettings, chartSettings } =
+      splitSquiggleChartSettings(props);
+
+    const {
+      code,
+      jsImports = defaultImports,
+      onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
+      executionId = 0,
+      width,
+      height = 200,
+      enableLocalSettings = false,
+      continues = defaultContinues,
+    } = props;
+
+    const p = React.useMemo(() => {
+      if (props.project) {
+        return props.project;
+      } else {
+        const p = SqProject.create();
+        if (props.environment) {
+          p.setEnvironment(props.environment);
+        }
+        return p;
+      }
+    }, [props.project, props.environment]);
+
+    const resultAndBindings = useSquiggle({
+      continues,
+      project: p,
+      code,
+      jsImports,
+      onChange,
+      executionId,
+    });
+
+    const valueToRender = getValueToRender(resultAndBindings);
 
     return (
       <SquiggleViewer
-        result={resultToRender}
+        result={valueToRender}
         width={width}
         height={height}
         distributionPlotSettings={distributionPlotSettings}

packages/components/src/components/SquiggleEditor.tsx

@@ -1,13 +1,21 @@
 import React from "react";
 import { CodeEditor } from "./CodeEditor";
 import { SquiggleContainer } from "./SquiggleContainer";
-import { SquiggleChart, SquiggleChartProps } from "./SquiggleChart";
+import {
-import { useMaybeControlledValue } from "../lib/hooks";
+  splitSquiggleChartSettings,
+  SquiggleChartProps,
+} from "./SquiggleChart";
+import { useMaybeControlledValue, useSquiggle } from "../lib/hooks";
+import { JsImports } from "../lib/jsImports";
+import { defaultEnvironment, SqLocation, SqProject } from "@quri/squiggle-lang";
+import { SquiggleViewer } from "./SquiggleViewer";
+import { getErrorLocations, getValueToRender } from "../lib/utility";
 
 const WrappedCodeEditor: React.FC<{
   code: string;
   setCode: (code: string) => void;
-}> = ({ code, setCode }) => (
+  errorLocations?: SqLocation[];
+}> = ({ code, setCode, errorLocations }) => (
   <div className="border border-grey-200 p-2 m-4">
     <CodeEditor
       value={code}
@@ -15,6 +23,7 @@ const WrappedCodeEditor: React.FC<{
       oneLine={true}
       showGutter={false}
       height={20}
+      errorLocations={errorLocations}
     />
   </div>
 );
@@ -24,6 +33,9 @@ export type SquiggleEditorProps = SquiggleChartProps & {
   onCodeChange?: (code: string) => void;
 };
 
+const defaultOnChange = () => {};
+const defaultImports: JsImports = {};
+
 export const SquiggleEditor: React.FC<SquiggleEditorProps> = (props) => {
   const [code, setCode] = useMaybeControlledValue({
     value: props.code,
@@ -31,11 +43,54 @@ export const SquiggleEditor: React.FC<SquiggleEditorProps> = (props) => {
     onChange: props.onCodeChange,
   });
 
-  let chartProps = { ...props, code };
+  const { distributionPlotSettings, chartSettings } =
+    splitSquiggleChartSettings(props);
+
+  const {
+    environment,
+    jsImports = defaultImports,
+    onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
+    executionId = 0,
+    width,
+    height = 200,
+    enableLocalSettings = false,
+  } = props;
+
+  const project = React.useMemo(() => {
+    const p = SqProject.create();
+    if (environment) {
+      p.setEnvironment(environment);
+    }
+    return p;
+  }, [environment]);
+
+  const resultAndBindings = useSquiggle({
+    code,
+    project,
+    jsImports,
+    onChange,
+    executionId,
+  });
+
+  const valueToRender = getValueToRender(resultAndBindings);
+  const errorLocations = getErrorLocations(resultAndBindings.result);
+
   return (
     <SquiggleContainer>
-      <WrappedCodeEditor code={code} setCode={setCode} />
+      <WrappedCodeEditor
-      <SquiggleChart {...chartProps} />
+        code={code}
+        setCode={setCode}
+        errorLocations={errorLocations}
+      />
+      <SquiggleViewer
+        result={valueToRender}
+        width={width}
+        height={height}
+        distributionPlotSettings={distributionPlotSettings}
+        chartSettings={chartSettings}
+        environment={environment ?? defaultEnvironment}
+        enableLocalSettings={enableLocalSettings}
+      />
     </SquiggleContainer>
   );
 };

packages/components/src/components/SquiggleErrorAlert.tsx

@@ -1,4 +1,4 @@
-import { SqError } from "@quri/squiggle-lang";
+import { SqError, SqFrame } from "@quri/squiggle-lang";
 import React from "react";
 import { ErrorAlert } from "./Alert";
 
@@ -6,6 +6,39 @@ type Props = {
   error: SqError;
 };
 
-export const SquiggleErrorAlert: React.FC<Props> = ({ error }) => {
+const StackTraceFrame: React.FC<{ frame: SqFrame }> = ({ frame }) => {
-  return <ErrorAlert heading="Error">{error.toString()}</ErrorAlert>;
+  const location = frame.location();
+  return (
+    <div>
+      {frame.name()}
+      {location
+        ? ` at line ${location.start.line}, column ${location.start.column}`
+        : ""}
+    </div>
+  );
+};
+
+const StackTrace: React.FC<Props> = ({ error }) => {
+  const frames = error.getFrameArray();
+  return frames.length ? (
+    <div>
+      <div className="font-medium">Stack trace:</div>
+      <div className="ml-4">
+        {frames.map((frame, i) => (
+          <StackTraceFrame frame={frame} key={i} />
+        ))}
+      </div>
+    </div>
+  ) : null;
+};
+
+export const SquiggleErrorAlert: React.FC<Props> = ({ error }) => {
+  return (
+    <ErrorAlert heading="Error">
+      <div className="space-y-4">
+        <div>{error.toString()}</div>
+        <StackTrace error={error} />
+      </div>
+    </ErrorAlert>
+  );
 };

packages/components/src/components/SquigglePlayground.tsx

@@ -8,7 +8,11 @@ import React, {
 } from "react";
 import { useForm, UseFormRegister, useWatch } from "react-hook-form";
 import * as yup from "yup";
-import { useMaybeControlledValue, useRunnerState } from "../lib/hooks";
+import {
+  useMaybeControlledValue,
+  useRunnerState,
+  useSquiggle,
+} from "../lib/hooks";
 import { yupResolver } from "@hookform/resolvers/yup";
 import {
   ChartSquareBarIcon,
@@ -24,9 +28,9 @@ import {
 } from "@heroicons/react/solid";
 import clsx from "clsx";
 
-import { environment } from "@quri/squiggle-lang";
+import { environment, SqProject } from "@quri/squiggle-lang";
 
-import { SquiggleChart, SquiggleChartProps } from "./SquiggleChart";
+import { SquiggleChartProps } from "./SquiggleChart";
 import { CodeEditor } from "./CodeEditor";
 import { JsonEditor } from "./JsonEditor";
 import { ErrorAlert, SuccessAlert } from "./Alert";
@@ -40,6 +44,8 @@ import { HeadedSection } from "./ui/HeadedSection";
 import { defaultTickFormat } from "../lib/distributionSpecBuilder";
 import { Button } from "./ui/Button";
 import { JsImports } from "../lib/jsImports";
+import { getErrorLocations, getValueToRender } from "../lib/utility";
+import { SquiggleViewer } from "./SquiggleViewer";
 
 type PlaygroundProps = SquiggleChartProps & {
   /** The initial squiggle string to put in the playground */
@@ -282,7 +288,7 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
     onSettingsChange?.(vars);
   }, [vars, onSettingsChange]);
 
-  const env: environment = useMemo(
+  const environment: environment = useMemo(
     () => ({
       sampleCount: Number(vars.sampleCount),
       xyPointLength: Number(vars.xyPointLength),
@@ -299,26 +305,59 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
     executionId,
   } = useRunnerState(code);
 
+  const project = React.useMemo(() => {
+    const p = SqProject.create();
+    if (environment) {
+      p.setEnvironment(environment);
+    }
+    return p;
+  }, [environment]);
+
+  const resultAndBindings = useSquiggle({
+    code,
+    project,
+    jsImports: imports,
+    executionId,
+  });
+
+  const valueToRender = getValueToRender(resultAndBindings);
+
   const squiggleChart =
     renderedCode === "" ? null : (
       <div className="relative">
         {isRunning ? (
           <div className="absolute inset-0 bg-white opacity-0 animate-semi-appear" />
         ) : null}
-        <SquiggleChart
+        <SquiggleViewer
-          code={renderedCode}
+          result={valueToRender}
-          executionId={executionId}
+          environment={environment}
-          environment={env}
+          height={vars.chartHeight || 150}
-          {...vars}
+          distributionPlotSettings={{
-          jsImports={imports}
+            showSummary: vars.showSummary ?? false,
+            logX: vars.logX ?? false,
+            expY: vars.expY ?? false,
+            format: vars.tickFormat,
+            minX: vars.minX,
+            maxX: vars.maxX,
+            title: vars.title,
+            actions: vars.distributionChartActions,
+          }}
+          chartSettings={{
+            start: vars.diagramStart ?? 0,
+            stop: vars.diagramStop ?? 10,
+            count: vars.diagramCount ?? 20,
+          }}
           enableLocalSettings={true}
         />
       </div>
     );
 
+  const errorLocations = getErrorLocations(resultAndBindings.result);
+
   const firstTab = vars.showEditor ? (
     <div className="border border-slate-200">
       <CodeEditor
+        errorLocations={errorLocations}
         value={code}
         onChange={setCode}
         onSubmit={run}

packages/components/src/components/SquiggleViewer/VariableBox.tsx

@@ -1,4 +1,4 @@
-import { SqValue, SqValueLocation } from "@quri/squiggle-lang";
+import { SqValue } from "@quri/squiggle-lang";
 import React, { useContext, useReducer } from "react";
 import { Tooltip } from "../ui/Tooltip";
 import { LocalItemSettings, MergedItemSettings } from "./utils";
@@ -70,7 +70,7 @@ export const VariableBox: React.FC<VariableBoxProps> = ({
         <div className="flex w-full">
           {location.path.items.length ? (
             <div
-              className="border-l-2 border-slate-200 hover:border-indigo-600 w-4 cursor-pointer"
+              className="shrink-0 border-l-2 border-slate-200 hover:border-indigo-600 w-4 cursor-pointer"
               onClick={toggleCollapsed}
             ></div>
           ) : null}

packages/components/src/lib/hooks/useSquiggle.ts

@@ -1,4 +1,10 @@
-import { SqProject, SqValue } from "@quri/squiggle-lang";
+import {
+  result,
+  SqError,
+  SqProject,
+  SqRecord,
+  SqValue,
+} from "@quri/squiggle-lang";
 import { useEffect, useMemo } from "react";
 import { JsImports, jsImportsToSquiggleCode } from "../jsImports";
 import * as uuid from "uuid";
@@ -8,29 +14,36 @@ type SquiggleArgs = {
   executionId?: number;
   jsImports?: JsImports;
   project: SqProject;
-  continues: string[];
+  continues?: string[];
   onChange?: (expr: SqValue | undefined, sourceName: string) => void;
 };
 
-const importSourceName = (sourceName: string) => "imports-" + sourceName;
+export type ResultAndBindings = {
+  result: result<SqValue, SqError>;
+  bindings: SqRecord;
+};
 
-export const useSquiggle = (args: SquiggleArgs) => {
+const importSourceName = (sourceName: string) => "imports-" + sourceName;
+const defaultContinues = [];
+
+export const useSquiggle = (args: SquiggleArgs): ResultAndBindings => {
   const sourceName = useMemo(() => uuid.v4(), []);
 
   const env = args.project.getEnvironment();
+  const continues = args.continues || defaultContinues;
 
   const result = useMemo(
     () => {
       const project = args.project;
 
       project.setSource(sourceName, args.code);
-      let continues = args.continues;
+      let fullContinues = continues;
       if (args.jsImports && Object.keys(args.jsImports).length) {
         const importsSource = jsImportsToSquiggleCode(args.jsImports);
         project.setSource(importSourceName(sourceName), importsSource);
-        continues = args.continues.concat(importSourceName(sourceName));
+        fullContinues = continues.concat(importSourceName(sourceName));
       }
-      project.setContinues(sourceName, continues);
+      project.setContinues(sourceName, fullContinues);
       project.run(sourceName);
       const result = project.getResult(sourceName);
       const bindings = project.getBindings(sourceName);
@@ -45,7 +58,7 @@ export const useSquiggle = (args: SquiggleArgs) => {
       args.jsImports,
       args.executionId,
       sourceName,
-      args.continues,
+      continues,
       args.project,
       env,
     ]

packages/components/src/lib/utility.ts

@@ -1,4 +1,5 @@
-import { result } from "@quri/squiggle-lang";
+import { result, resultMap, SqValueTag } from "@quri/squiggle-lang";
+import { ResultAndBindings } from "./hooks/useSquiggle";
 
 export function flattenResult<a, b>(x: result<a, b>[]): result<a[], b> {
   if (x.length === 0) {
@@ -35,3 +36,18 @@ export function all(arr: boolean[]): boolean {
 export function some(arr: boolean[]): boolean {
   return arr.reduce((x, y) => x || y, false);
 }
+
+export function getValueToRender({ result, bindings }: ResultAndBindings) {
+  return resultMap(result, (value) =>
+    value.tag === SqValueTag.Void ? bindings.asValue() : value
+  );
+}
+
+export function getErrorLocations(result: ResultAndBindings["result"]) {
+  if (result.tag === "Error") {
+    const location = result.value.location();
+    return location ? [location] : [];
+  } else {
+    return [];
+  }
+}

packages/components/src/styles/main.css

@@ -22,3 +22,8 @@ but this line is still necessary for proper initialization of `--tw-*` variables
 .ace_cursor {
   border-left: 2px solid !important;
 }
+
+.ace-error-marker {
+  position: absolute;
+  border-bottom: 1px solid red;
+}

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_Parse_test.res

@@ -197,7 +197,7 @@ describe("Peggy parse", () => {
 
   describe("lambda", () => {
     testParse("{|x| x}", "{{|:x| :x}}")
-    testParse("f={|x| x}", "{:f = {{|:x| :x}}}")
+    testParse("f={|x| x}", "{:f = {|:x| :x}}")
     testParse("f(x)=x", "{:f = {|:x| {:x}}}") // Function definitions are lambda assignments
     testParse("f(x)=x ? 1 : 0", "{:f = {|:x| {(::$$_ternary_$$ :x 1 0)}}}") // Function definitions are lambda assignments
   })

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_TestHelpers.res

@@ -9,12 +9,12 @@ open Jest
 open Expect
 
 let expectParseToBe = (expr, answer) =>
-  Parse.parse(expr)->Parse.toStringResult->expect->toBe(answer)
+  Parse.parse(expr, "test")->Parse.toStringResult->expect->toBe(answer)
 
 let testParse = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
 
-let expectToExpressionToBe = (expr, answer, ~v="_", ()) => {
+let expectExpressionToBe = (expr, answer, ~v="_", ()) => {
-  let rExpr = Parse.parse(expr)->Result.map(ToExpression.fromNode)
+  let rExpr = Parse.parse(expr, "test")->Result.map(ToExpression.fromNode)
   let a1 = rExpr->ExpressionT.toStringResultOkless
 
   if v == "_" {
@@ -22,6 +22,7 @@ let expectToExpressionToBe = (expr, answer, ~v="_", ()) => {
   } else {
     let a2 =
       rExpr
+      ->E.R2.errMap(e => e->SqError.fromParseError)
       ->Result.flatMap(expr => Expression.BackCompatible.evaluate(expr))
       ->Reducer_Value.toStringResultOkless
     (a1, a2)->expect->toEqual((answer, v))
@@ -29,16 +30,16 @@ let expectToExpressionToBe = (expr, answer, ~v="_", ()) => {
 }
 
 let testToExpression = (expr, answer, ~v="_", ()) =>
-  test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
+  test(expr, () => expectExpressionToBe(expr, answer, ~v, ()))
 
 module MyOnly = {
   let testParse = (expr, answer) => Only.test(expr, () => expectParseToBe(expr, answer))
   let testToExpression = (expr, answer, ~v="_", ()) =>
-    Only.test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
+    Only.test(expr, () => expectExpressionToBe(expr, answer, ~v, ()))
 }
 
 module MySkip = {
   let testParse = (expr, answer) => Skip.test(expr, () => expectParseToBe(expr, answer))
   let testToExpression = (expr, answer, ~v="_", ()) =>
-    Skip.test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
+    Skip.test(expr, () => expectExpressionToBe(expr, answer, ~v, ()))
 }

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_ToExpression_test.res

@@ -135,7 +135,7 @@ describe("Peggy to Expression", () => {
 
   describe("lambda", () => {
     testToExpression("{|x| x}", "{|x| x}", ~v="lambda(x=>internal code)", ())
-    testToExpression("f={|x| x}", "f = {{|x| x}}", ())
+    testToExpression("f={|x| x}", "f = {|x| x}", ())
     testToExpression("f(x)=x", "f = {|x| {x}}", ()) // Function definitions are lambda assignments
     testToExpression("f(x)=x ? 1 : 0", "f = {|x| {x ? (1) : (0)}}", ())
   })

packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res

@@ -1,4 +1,3 @@
-module ErrorValue = Reducer_ErrorValue
 module Expression = Reducer_Expression
 module ExpressionT = Reducer_Expression_T
 
@@ -9,7 +8,7 @@ let unwrapRecord = rValue =>
   rValue->Belt.Result.flatMap(value =>
     switch value {
     | Reducer_T.IEvRecord(aRecord) => Ok(aRecord)
-    | _ => ErrorValue.RETodo("TODO: Internal bindings must be returned")->Error
+    | _ => SqError.Message.RETodo("TODO: Internal bindings must be returned")->Error
     }
   )
 

packages/squiggle-lang/__tests__/Reducer/Reducer_test.res

@@ -70,7 +70,7 @@ describe("test exceptions", () => {
   testDescriptionEvalToBe(
     "javascript exception",
     "javascriptraise('div by 0')",
-    "Error(Error: 'div by 0')",
+    "Error(JS Exception: Error: 'div by 0')",
   )
   // testDescriptionEvalToBe(
   //   "rescript exception",
@@ -78,3 +78,33 @@ describe("test exceptions", () => {
   //   "Error(TODO: unhandled rescript exception)",
   // )
 })
+
+describe("stacktraces", () => {
+  test("nested calls", () => {
+    open Expect
+
+    let error =
+      Expression.BackCompatible.evaluateString(`
+  f(x) = {
+    y = "a"
+    x + y
+  }
+  g = {|x| f(x)}
+  h(x) = g(x)
+  h(5)
+`)
+      ->E.R.getError
+      ->E.O2.toExn("oops")
+      ->SqError.toStringWithStackTrace
+
+    expect(
+      error,
+    )->toBe(`Error: There are function matches for add(), but with different arguments: [add(number, number)]; [add(distribution, number)]; [add(number, distribution)]; [add(distribution, distribution)]; [add(date, duration)]; [add(duration, duration)]
+Stack trace:
+  f at line 4, column 5
+  g at line 6, column 12
+  h at line 7, column 10
+  <top> at line 8, column 3
+`)
+  })
+})

packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_includes_test.res

@@ -25,7 +25,7 @@ x=1`,
     let mainIncludes = Project.getIncludes(project, "main")
     switch mainIncludes {
     | Ok(includes) => expect(includes) == ["common"]
-    | Error(error) => fail(error->Reducer_ErrorValue.errorToString)
+    | Error(error) => fail(error->SqError.toString)
     }
   })
   test("past chain", () => {
@@ -60,7 +60,7 @@ x=1`,
     let mainIncludes = Project.getIncludes(project, "main")
     switch mainIncludes {
     | Ok(includes) => expect(includes) == ["common", "myModule"]
-    | Error(error) => fail(error->Reducer_ErrorValue.errorToString)
+    | Error(error) => fail(error->SqError.toString)
     }
   })
 
@@ -99,7 +99,7 @@ x=1`,
     let mainIncludes = Project.getIncludes(project, "main")
     switch mainIncludes {
     | Ok(includes) => expect(includes) == ["common", "common2", "myModule"]
-    | Error(error) => fail(error->Reducer_ErrorValue.errorToString)
+    | Error(error) => fail(error->SqError.toString)
     }
   })
   test("direct past chain", () => {

packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_3_includes_test.res

@@ -36,7 +36,7 @@ Here we will finally proceed to a real life scenario. */
       /* Parse includes has set the includes */
       switch project->Project.getIncludes("main") {
       | Ok(includes) => includes->expect == ["common"]
-      | Error(err) => err->Reducer_ErrorValue.errorToString->fail
+      | Error(err) => err->SqError.toString->fail
       }
       /* If the includes cannot be parsed then you get a syntax error.
       Otherwise you get the includes.
@@ -85,7 +85,7 @@ Here we will finally proceed to a real life scenario. */
           let rIncludes = project->Project.getIncludes(sourceName)
           switch rIncludes {
           /* Maybe there is an include syntax error */
-          | Error(err) => err->Reducer_ErrorValue.errorToString->Js.Exn.raiseError
+          | Error(err) => err->SqError.toString->Js.Exn.raiseError
 
           | Ok(includes) =>
             includes->Belt.Array.forEach(newIncludeName => {
@@ -169,7 +169,7 @@ Here we will finally proceed to a real life scenario. */
     test("getIncludes", () => {
       switch Project.getIncludes(project, "main") {
       | Ok(includes) => includes->expect == ["common"]
-      | Error(err) => err->Reducer_ErrorValue.errorToString->fail
+      | Error(err) => err->SqError.toString->fail
       }
     })
   })

packages/squiggle-lang/__tests__/SqError_test.res

@@ -0,0 +1,41 @@
+open Jest
+open Expect
+
+describe("SqError.Message", () => {
+  test("toString", () =>
+    expect(SqError.Message.REOther("test error")->SqError.Message.toString)->toBe(
+      "Error: test error",
+    )
+  )
+})
+
+describe("SqError", () => {
+  test("fromMessage", () =>
+    expect(SqError.Message.REOther("test error")->SqError.fromMessage->SqError.toString)->toBe(
+      "Error: test error",
+    )
+  )
+
+  test("toStringWithStackTrace with empty stacktrace", () =>
+    expect(
+      SqError.Message.REOther("test error")->SqError.fromMessage->SqError.toStringWithStackTrace,
+    )->toBe("Error: test error")
+  )
+
+  test("toStringWithStackTrace", () => {
+    let frameStack =
+      Reducer_FrameStack.make()
+      ->Reducer_FrameStack.extend("frame1", None)
+      ->Reducer_FrameStack.extend("frame2", None)
+
+    expect(
+      SqError.Message.REOther("test error")
+      ->SqError.fromMessageWithFrameStack(frameStack)
+      ->SqError.toStringWithStackTrace,
+    )->toBe(`Error: test error
+Stack trace:
+  frame2
+  frame1
+`)
+  })
+})

packages/squiggle-lang/scripts/lib.mjs

@@ -36,6 +36,6 @@ export const run = (src, { output, sampleCount } = {}) => {
     "Time:",
     String(time),
     result.tag === "Error" ? red(result.tag) : green(result.tag),
-    result.tag === "Error" ? result.value.toString() : ""
+    result.tag === "Error" ? result.value.toStringWithFrameStack() : ""
   );
 };

packages/squiggle-lang/scripts/run.mjs

@@ -1,11 +1,18 @@
 #!/usr/bin/env node
 import { run } from "./lib.mjs";
 
-const src = process.argv[2];
+import { Command } from "commander";
+
+const program = new Command();
+
+program.arguments("<string>");
+
+const options = program.parse(process.argv);
+
+const src = program.args[0];
 if (!src) {
   throw new Error("Expected src");
 }
-console.log(`Running ${src}`);
 
 const sampleCount = process.env.SAMPLE_COUNT;
 

packages/squiggle-lang/src/js/SqError.ts

@@ -1,17 +1,48 @@
-import * as RSErrorValue from "../rescript/ForTS/ForTS_Reducer_ErrorValue.gen";
+import * as RSError from "../rescript/SqError.gen";
+import * as RSReducerT from "../rescript/Reducer/Reducer_T.gen";
+
+import * as RSFrameStack from "../rescript/Reducer/Reducer_FrameStack.gen";
+
+export { location as SqLocation } from "../rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.gen";
 
 export class SqError {
-  constructor(private _value: RSErrorValue.reducerErrorValue) {}
+  constructor(private _value: RSError.t) {}
 
   toString() {
-    return RSErrorValue.toString(this._value);
+    return RSError.toString(this._value);
   }
 
-  static createTodoError(v: string) {
+  toStringWithStackTrace() {
-    return new SqError(RSErrorValue.createTodoError(v));
+    return RSError.toStringWithStackTrace(this._value);
   }
 
   static createOtherError(v: string) {
-    return new SqError(RSErrorValue.createOtherError(v));
+    return new SqError(RSError.createOtherError(v));
+  }
+
+  getTopFrame(): SqFrame | undefined {
+    const frame = RSFrameStack.getTopFrame(RSError.getFrameStack(this._value));
+    return frame ? new SqFrame(frame) : undefined;
+  }
+
+  getFrameArray(): SqFrame[] {
+    const frames = RSError.getFrameArray(this._value);
+    return frames.map((frame) => new SqFrame(frame));
+  }
+
+  location() {
+    return this.getTopFrame()?.location();
+  }
+}
+
+export class SqFrame {
+  constructor(private _value: RSReducerT.frame) {}
+
+  name(): string {
+    return RSFrameStack.Frame.getName(this._value);
+  }
+
+  location() {
+    return RSFrameStack.Frame.getLocation(this._value);
   }
 }

packages/squiggle-lang/src/js/SqProject.ts

@@ -1,5 +1,5 @@
 import * as RSProject from "../rescript/ForTS/ForTS_ReducerProject.gen";
-import { reducerErrorValue } from "../rescript/ForTS/ForTS_Reducer_ErrorValue.gen";
+import * as RSError from "../rescript/SqError.gen";
 import { environment } from "../rescript/ForTS/ForTS_Distribution/ForTS_Distribution_Environment.gen";
 import { SqError } from "./SqError";
 import { SqRecord } from "./SqRecord";
@@ -54,7 +54,7 @@ export class SqProject {
     return resultMap2(
       RSProject.getIncludes(this._value, sourceId),
       (a) => a,
-      (v: reducerErrorValue) => new SqError(v)
+      (v: RSError.t) => new SqError(v)
     );
   }
 
@@ -108,7 +108,7 @@ export class SqProject {
             items: [],
           })
         ),
-      (v: reducerErrorValue) => new SqError(v)
+      (v: RSError.t) => new SqError(v)
     );
   }
 

packages/squiggle-lang/src/js/SqValueLocation.ts

@@ -1,4 +1,3 @@
-import { isParenthesisNode } from "mathjs";
 import { SqProject } from "./SqProject";
 
 type PathItem = string | number;

packages/squiggle-lang/src/js/index.ts

@@ -13,7 +13,7 @@ export {
   environment,
   defaultEnvironment,
 } from "../rescript/ForTS/ForTS_Distribution/ForTS_Distribution.gen";
-export { SqError } from "./SqError";
+export { SqError, SqFrame, SqLocation } from "./SqError";
 export { SqShape } from "./SqPointSetDist";
 
 export { resultMap } from "./types";

packages/squiggle-lang/src/rescript/FR/FR_Builtin.res

@@ -5,7 +5,7 @@ let nameSpace = "" // no namespaced versions
 
 type simpleDefinition = {
   inputs: array<frType>,
-  fn: array<Reducer_T.value> => result<Reducer_T.value, errorValue>,
+  fn: array<Reducer_T.value> => result<Reducer_T.value, errorMessage>,
 }
 
 let makeFnMany = (name: string, definitions: array<simpleDefinition>) =>
@@ -22,7 +22,7 @@ let makeFnMany = (name: string, definitions: array<simpleDefinition>) =>
 let makeFn = (
   name: string,
   inputs: array<frType>,
-  fn: array<Reducer_T.value> => result<Reducer_T.value, errorValue>,
+  fn: array<Reducer_T.value> => result<Reducer_T.value, errorMessage>,
 ) => makeFnMany(name, [{inputs: inputs, fn: fn}])
 
 let library = [

packages/squiggle-lang/src/rescript/FR/FR_Danger.res

@@ -67,7 +67,7 @@ module Integration = {
       let applyFunctionAtFloatToFloatOption = (point: float) => {
         // Defined here so that it has access to environment, reducer
         let pointAsInternalExpression = FunctionRegistry_Helpers.Wrappers.evNumber(point)
-        let resultAsInternalExpression = Reducer_Expression_Lambda.doLambdaCall(
+        let resultAsInternalExpression = Reducer_Lambda.doLambdaCall(
           aLambda,
           [pointAsInternalExpression],
           environment,
@@ -77,7 +77,7 @@ module Integration = {
         | Reducer_T.IEvNumber(x) => Ok(x)
         | _ =>
           Error(
-            "Error 1 in Danger.integrate. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead"->Reducer_ErrorValue.REOther,
+            "Error 1 in Danger.integrate. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead"->SqError.Message.REOther,
           )
         }
         result
@@ -143,8 +143,8 @@ module Integration = {
       | Error(b) =>
         ("Integration error 2 in Danger.integrate. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead." ++
         "Original error: " ++
-        b->Reducer_ErrorValue.errorToString)
+        b->SqError.Message.toString)
-        ->Reducer_ErrorValue.REOther
+        ->SqError.Message.REOther
         ->Error
       }
       result
@@ -169,7 +169,7 @@ module Integration = {
             let result = switch inputs {
             | [_, _, _, IEvNumber(0.0)] =>
               "Integration error 4 in Danger.integrate: Increment can't be 0."
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             | [
                 IEvLambda(aLambda),
@@ -187,7 +187,7 @@ module Integration = {
               )
             | _ =>
               Error(
-                Reducer_ErrorValue.REOther(
+                SqError.Message.REOther(
                   "Integration error 5 in Danger.integrate. Remember that inputs are (function, number (min), number (max), number(increment))",
                 ),
               )
@@ -213,7 +213,7 @@ module Integration = {
             let result = switch inputs {
             | [_, _, _, IEvNumber(0.0)] =>
               "Integration error in Danger.integrate: Increment can't be 0."
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             | [IEvLambda(aLambda), IEvNumber(min), IEvNumber(max), IEvNumber(epsilon)] =>
               Helpers.integrateFunctionBetweenWithNumIntegrationPoints(
@@ -225,11 +225,11 @@ module Integration = {
                 reducer,
               )->E.R2.errMap(b =>
                 ("Integration error 7 in Danger.integrate. Something went wrong along the way: " ++
-                b->Reducer_ErrorValue.errorToString)->Reducer_ErrorValue.REOther
+                b->SqError.Message.toString)->SqError.Message.REOther
               )
             | _ =>
               "Integration error 8 in Danger.integrate. Remember that inputs are (function, number (min), number (max), number(increment))"
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             }
             result
@@ -246,7 +246,7 @@ module DiminishingReturns = {
   module Helpers = {
     type diminishingReturnsAccumulatorInner = {
       optimalAllocations: array<float>,
-      currentMarginalReturns: result<array<float>, errorValue>,
+      currentMarginalReturns: result<array<float>, errorMessage>,
     }
     let findBiggestElementIndex = (xs: array<float>) =>
       E.A.reducei(xs, 0, (acc, newElement, index) => {
@@ -255,7 +255,7 @@ module DiminishingReturns = {
         | false => acc
         }
       })
-    type diminishingReturnsAccumulator = result<diminishingReturnsAccumulatorInner, errorValue>
+    type diminishingReturnsAccumulator = result<diminishingReturnsAccumulatorInner, errorMessage>
     // TODO: This is so complicated, it probably should be its own file. It might also make sense to have it work in Rescript directly, taking in a function rather than a reducer; then something else can wrap that function in the reducer/lambdas/environment.
     /*
     The key idea for this function is that 
@@ -290,25 +290,25 @@ module DiminishingReturns = {
       ) {
       | (false, _, _, _) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, number of functions should be greater than 1."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, number of functions should be greater than 1."->SqError.Message.REOther,
         )
       | (_, false, _, _) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, funds should be greater than 0."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, funds should be greater than 0."->SqError.Message.REOther,
         )
       | (_, _, false, _) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be greater than 0."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be greater than 0."->SqError.Message.REOther,
         )
       | (_, _, _, false) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be smaller than funds amount."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be smaller than funds amount."->SqError.Message.REOther,
         )
       | (true, true, true, true) => {
           let applyFunctionAtPoint = (lambda, point: float) => {
             // Defined here so that it has access to environment, reducer
             let pointAsInternalExpression = FunctionRegistry_Helpers.Wrappers.evNumber(point)
-            let resultAsInternalExpression = Reducer_Expression_Lambda.doLambdaCall(
+            let resultAsInternalExpression = Reducer_Lambda.doLambdaCall(
               lambda,
               [pointAsInternalExpression],
               environment,
@@ -318,7 +318,7 @@ module DiminishingReturns = {
             | Reducer_T.IEvNumber(x) => Ok(x)
             | _ =>
               Error(
-                "Error 1 in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead"->Reducer_ErrorValue.REOther,
+                "Error 1 in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead"->SqError.Message.REOther,
               )
             }
           }
@@ -411,7 +411,7 @@ module DiminishingReturns = {
                   | Reducer_T.IEvLambda(lambda) => Ok(lambda)
                   | _ =>
                     "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions. A member of the array wasn't a function"
-                    ->Reducer_ErrorValue.REOther
+                    ->SqError.Message.REOther
                     ->Error
                   }
                 }, innerlambdas)
@@ -433,7 +433,7 @@ module DiminishingReturns = {
               }
             | _ =>
               "Error in Danger.diminishingMarginalReturnsForTwoFunctions"
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             },
           (),

packages/squiggle-lang/src/rescript/FR/FR_Date.res

@@ -4,7 +4,7 @@ open FunctionRegistry_Helpers
 let makeFn = (
   name: string,
   inputs: array<frType>,
-  fn: array<Reducer_T.value> => result<Reducer_T.value, errorValue>,
+  fn: array<Reducer_T.value> => result<Reducer_T.value, errorMessage>,
 ) =>
   Function.make(
     ~name,
@@ -66,7 +66,7 @@ let library = [
     | [IEvNumber(year)] =>
       switch DateTime.Date.makeFromYear(year) {
       | Ok(t) => IEvDate(t)->Ok
-      | Error(e) => Reducer_ErrorValue.RETodo(e)->Error
+      | Error(e) => SqError.Message.RETodo(e)->Error
       }
     | _ => Error(impossibleError)
     }

packages/squiggle-lang/src/rescript/FR/FR_Dict.res

@@ -17,7 +17,7 @@ module Internals = {
     ->E.A2.fmap(((key, value)) => Wrappers.evArray([IEvString(key), value]))
     ->Wrappers.evArray
 
-  let fromList = (items: array<Reducer_T.value>): result<Reducer_T.value, errorValue> =>
+  let fromList = (items: array<Reducer_T.value>): result<Reducer_T.value, errorMessage> =>
     items
     ->E.A2.fmap(item => {
       switch (item: Reducer_T.value) {
@@ -76,7 +76,7 @@ let library = [
             ->Belt.Array.map(dictValue =>
               switch dictValue {
               | IEvRecord(dict) => dict
-              | _ => impossibleError->Reducer_ErrorValue.toException
+              | _ => impossibleError->SqError.Message.throw
               }
             )
             ->Internals.mergeMany

packages/squiggle-lang/src/rescript/FR/FR_Dist.res

@@ -16,13 +16,14 @@ module DistributionCreation = {
       r
       ->E.R.bind(Process.DistOrNumberToDist.twoValuesUsingSymbolicDist(~fn, ~values=_, ~env))
       ->E.R2.fmap(Wrappers.evDistribution)
-      ->E.R2.errMap(e => Reducer_ErrorValue.REOther(e))
+      ->E.R2.errMap(e => SqError.Message.REOther(e))
 
     let make = (name, fn) => {
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeDistOrNumber, FRTypeDistOrNumber],
-        ~run=(inputs, env, _) => inputs->Prepare.ToValueTuple.twoDistOrNumber->process(~fn, ~env),
+        ~run=(inputs, context, _) =>
+          inputs->Prepare.ToValueTuple.twoDistOrNumber->process(~fn, ~env=context.environment),
         (),
       )
     }
@@ -31,8 +32,10 @@ module DistributionCreation = {
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeRecord([("p5", FRTypeDistOrNumber), ("p95", FRTypeDistOrNumber)])],
-        ~run=(inputs, env, _) =>
+        ~run=(inputs, context, _) =>
-          inputs->Prepare.ToValueTuple.Record.twoDistOrNumber(("p5", "p95"))->process(~fn, ~env),
+          inputs
+          ->Prepare.ToValueTuple.Record.twoDistOrNumber(("p5", "p95"))
+          ->process(~fn, ~env=context.environment),
         (),
       )
     }
@@ -41,10 +44,10 @@ module DistributionCreation = {
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeRecord([("mean", FRTypeDistOrNumber), ("stdev", FRTypeDistOrNumber)])],
-        ~run=(inputs, env, _) =>
+        ~run=(inputs, context, _) =>
           inputs
           ->Prepare.ToValueTuple.Record.twoDistOrNumber(("mean", "stdev"))
-          ->process(~fn, ~env),
+          ->process(~fn, ~env=context.environment),
         (),
       )
     }
@@ -55,13 +58,14 @@ module DistributionCreation = {
       r
       ->E.R.bind(Process.DistOrNumberToDist.oneValueUsingSymbolicDist(~fn, ~value=_, ~env))
       ->E.R2.fmap(Wrappers.evDistribution)
-      ->E.R2.errMap(e => Reducer_ErrorValue.REOther(e))
+      ->E.R2.errMap(e => SqError.Message.REOther(e))
 
     let make = (name, fn) =>
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeDistOrNumber],
-        ~run=(inputs, env, _) => inputs->Prepare.ToValueTuple.oneDistOrNumber->process(~fn, ~env),
+        ~run=(inputs, context, _) =>
+          inputs->Prepare.ToValueTuple.oneDistOrNumber->process(~fn, ~env=context.environment),
         (),
       )
   }

packages/squiggle-lang/src/rescript/FR/FR_GenericDist.res

@@ -296,7 +296,7 @@ module Old = {
 
   let genericOutputToReducerValue = (o: DistributionOperation.outputType): result<
     Reducer_T.value,
-    Reducer_ErrorValue.errorValue,
+    SqError.Message.t,
   > =>
     switch o {
     | Dist(d) => Ok(Reducer_T.IEvDistribution(d))
@@ -311,9 +311,9 @@ module Old = {
     switch dispatchToGenericOutput(call, environment) {
     | Some(o) => genericOutputToReducerValue(o)
     | None =>
-      Reducer_ErrorValue.REOther("Internal error in FR_GenericDist implementation")
+      SqError.Message.REOther(
-      ->Reducer_ErrorValue.ErrorException
+        "Internal error in FR_GenericDist implementation",
-      ->raise
+      )->SqError.Message.throw
     }
 }
 
@@ -326,7 +326,7 @@ let makeProxyFn = (name: string, inputs: array<frType>) => {
       FnDefinition.make(
         ~name,
         ~inputs,
-        ~run=(inputs, env, _) => Old.dispatch((name, inputs), env),
+        ~run=(inputs, context, _) => Old.dispatch((name, inputs), context.environment),
         (),
       ),
     ],
@@ -402,9 +402,9 @@ let library = E.A.concatMany([
 ])
 
 // FIXME - impossible to implement with FR due to arbitrary parameters length;
-let mxLambda = Reducer_Expression_Lambda.makeFFILambda((inputs, env, _) => {
+let mxLambda = Reducer_Lambda.makeFFILambda("mx", (inputs, context, _) => {
-  switch Old.dispatch(("mx", inputs), env) {
+  switch Old.dispatch(("mx", inputs), context.environment) {
   | Ok(value) => value
-  | Error(e) => e->Reducer_ErrorValue.ErrorException->raise
+  | Error(e) => e->SqError.Message.throw
   }
 })

packages/squiggle-lang/src/rescript/FR/FR_List.res

@@ -30,11 +30,11 @@ module Internals = {
   let map = (
     array: array<Reducer_T.value>,
     eLambdaValue,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
   ): Reducer_T.value => {
     Belt.Array.map(array, elem =>
-      Reducer_Expression_Lambda.doLambdaCall(eLambdaValue, [elem], env, reducer)
+      Reducer_Lambda.doLambdaCall(eLambdaValue, [elem], context, reducer)
     )->Wrappers.evArray
   }
 
@@ -42,11 +42,11 @@ module Internals = {
     aValueArray,
     initialValue,
     aLambdaValue,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
   ) => {
     aValueArray->E.A.reduce(initialValue, (acc, elem) =>
-      Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, [acc, elem], env, reducer)
+      Reducer_Lambda.doLambdaCall(aLambdaValue, [acc, elem], context, reducer)
     )
   }
 
@@ -54,22 +54,22 @@ module Internals = {
     aValueArray,
     initialValue,
     aLambdaValue,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
   ) => {
     aValueArray->Belt.Array.reduceReverse(initialValue, (acc, elem) =>
-      Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, [acc, elem], env, reducer)
+      Reducer_Lambda.doLambdaCall(aLambdaValue, [acc, elem], context, reducer)
     )
   }
 
   let filter = (
     aValueArray,
     aLambdaValue,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
   ) => {
     Js.Array2.filter(aValueArray, elem => {
-      let result = Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, [elem], env, reducer)
+      let result = Reducer_Lambda.doLambdaCall(aLambdaValue, [elem], context, reducer)
       switch result {
       | IEvBool(true) => true
       | _ => false

packages/squiggle-lang/src/rescript/FR/FR_Pointset.res

@@ -16,30 +16,30 @@ let inputsToDist = (inputs: array<Reducer_T.value>, xyShapeToPointSetDist) => {
           let yValue = map->Belt.Map.String.get("y")
           switch (xValue, yValue) {
           | (Some(IEvNumber(x)), Some(IEvNumber(y))) => (x, y)
-          | _ => impossibleError->Reducer_ErrorValue.toException
+          | _ => impossibleError->SqError.Message.throw
           }
         }
-      | _ => impossibleError->Reducer_ErrorValue.toException
+      | _ => impossibleError->SqError.Message.throw
       }
     )
     ->Ok
     ->E.R.bind(r => r->XYShape.T.makeFromZipped->E.R2.errMap(XYShape.Error.toString))
     ->E.R2.fmap(r => Reducer_T.IEvDistribution(PointSet(r->xyShapeToPointSetDist)))
-  | _ => impossibleError->Reducer_ErrorValue.toException
+  | _ => impossibleError->SqError.Message.throw
   }
 }
 
 module Internal = {
   type t = PointSetDist.t
 
-  let toType = (r): result<Reducer_T.value, Reducer_ErrorValue.errorValue> =>
+  let toType = (r): result<Reducer_T.value, SqError.Message.t> =>
     switch r {
     | Ok(r) => Ok(Wrappers.evDistribution(PointSet(r)))
     | Error(err) => Error(REOperationError(err))
     }
 
   let doLambdaCall = (aLambdaValue, list, env, reducer) =>
-    switch Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list, env, reducer) {
+    switch Reducer_Lambda.doLambdaCall(aLambdaValue, list, env, reducer) {
     | Reducer_T.IEvNumber(f) => Ok(f)
     | _ => Error(Operation.SampleMapNeedsNtoNFunction)
     }
@@ -61,18 +61,18 @@ let library = [
       FnDefinition.make(
         ~name="fromDist",
         ~inputs=[FRTypeDist],
-        ~run=(inputs, env, _) =>
+        ~run=(inputs, context, _) =>
           switch inputs {
           | [IEvDistribution(dist)] =>
             GenericDist.toPointSet(
               dist,
-              ~xyPointLength=env.xyPointLength,
+              ~xyPointLength=context.environment.xyPointLength,
-              ~sampleCount=env.sampleCount,
+              ~sampleCount=context.environment.sampleCount,
               (),
             )
             ->E.R2.fmap(Wrappers.pointSet)
             ->E.R2.fmap(Wrappers.evDistribution)
-            ->E.R2.errMap(e => Reducer_ErrorValue.REDistributionError(e))
+            ->E.R2.errMap(e => SqError.Message.REDistributionError(e))
           | _ => Error(impossibleError)
           },
         (),

packages/squiggle-lang/src/rescript/FR/FR_Sampleset.res

@@ -10,41 +10,40 @@ module Internal = {
   let doLambdaCall = (
     aLambdaValue,
     list,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
   ) =>
-    switch Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list, env, reducer) {
+    switch Reducer_Lambda.doLambdaCall(aLambdaValue, list, context, reducer) {
     | IEvNumber(f) => Ok(f)
     | _ => Error(Operation.SampleMapNeedsNtoNFunction)
     }
 
-  let toType = (r): result<Reducer_T.value, Reducer_ErrorValue.errorValue> =>
+  let toType = (r): result<Reducer_T.value, SqError.Message.t> =>
     switch r {
     | Ok(r) => Ok(Wrappers.evDistribution(SampleSet(r)))
     | Error(r) => Error(REDistributionError(SampleSetError(r)))
     }
 
   //TODO: I don't know why this seems to need at least one input
-  let fromFn = (aLambdaValue, environment: Reducer_T.environment, reducer: Reducer_T.reducerFn) => {
+  let fromFn = (aLambdaValue, context: Reducer_T.context, reducer: Reducer_T.reducerFn) => {
-    let sampleCount = environment.sampleCount
+    let sampleCount = context.environment.sampleCount
-    let fn = r => doLambdaCall(aLambdaValue, [IEvNumber(r)], environment, reducer)
+    let fn = r => doLambdaCall(aLambdaValue, [IEvNumber(r)], context, reducer)
     Belt_Array.makeBy(sampleCount, r => fn(r->Js.Int.toFloat))->E.A.R.firstErrorOrOpen
   }
 
-  let map1 = (sampleSetDist: t, aLambdaValue, environment: Reducer_T.environment, reducer) => {
+  let map1 = (sampleSetDist: t, aLambdaValue, context: Reducer_T.context, reducer) => {
-    let fn = r => doLambdaCall(aLambdaValue, [IEvNumber(r)], environment, reducer)
+    let fn = r => doLambdaCall(aLambdaValue, [IEvNumber(r)], context, reducer)
     SampleSetDist.samplesMap(~fn, sampleSetDist)->toType
   }
 
-  let map2 = (t1: t, t2: t, aLambdaValue, environment: Reducer_T.environment, reducer) => {
+  let map2 = (t1: t, t2: t, aLambdaValue, context: Reducer_T.context, reducer) => {
-    let fn = (a, b) =>
+    let fn = (a, b) => doLambdaCall(aLambdaValue, [IEvNumber(a), IEvNumber(b)], context, reducer)
-      doLambdaCall(aLambdaValue, [IEvNumber(a), IEvNumber(b)], environment, reducer)
     SampleSetDist.map2(~fn, ~t1, ~t2)->toType
   }
 
-  let map3 = (t1: t, t2: t, t3: t, aLambdaValue, environment: Reducer_T.environment, reducer) => {
+  let map3 = (t1: t, t2: t, t3: t, aLambdaValue, context: Reducer_T.context, reducer) => {
     let fn = (a, b, c) =>
-      doLambdaCall(aLambdaValue, [IEvNumber(a), IEvNumber(b), IEvNumber(c)], environment, reducer)
+      doLambdaCall(aLambdaValue, [IEvNumber(a), IEvNumber(b), IEvNumber(c)], context, reducer)
     SampleSetDist.map3(~fn, ~t1, ~t2, ~t3)->toType
   }
 
@@ -60,7 +59,7 @@ module Internal = {
   let mapN = (
     aValueArray: array<Reducer_T.value>,
     aLambdaValue,
-    environment: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer,
   ) => {
     switch parseSampleSetArray(aValueArray) {
@@ -69,7 +68,7 @@ module Internal = {
         doLambdaCall(
           aLambdaValue,
           [IEvArray(E.A.fmap(x => Wrappers.evNumber(x), a))],
-          environment,
+          context,
           reducer,
         )
       SampleSetDist.mapN(~fn, ~t1)->toType
@@ -89,13 +88,13 @@ let libaryBase = [
       FnDefinition.make(
         ~name="fromDist",
         ~inputs=[FRTypeDist],
-        ~run=(inputs, environment, _) =>
+        ~run=(inputs, context, _) =>
           switch inputs {
           | [IEvDistribution(dist)] =>
-            GenericDist.toSampleSetDist(dist, environment.sampleCount)
+            GenericDist.toSampleSetDist(dist, context.environment.sampleCount)
             ->E.R2.fmap(Wrappers.sampleSet)
             ->E.R2.fmap(Wrappers.evDistribution)
-            ->E.R2.errMap(e => Reducer_ErrorValue.REDistributionError(e))
+            ->E.R2.errMap(e => SqError.Message.REDistributionError(e))
           | _ => Error(impossibleError)
           },
         (),
@@ -163,7 +162,7 @@ let libaryBase = [
           | [IEvLambda(lambda)] =>
             switch Internal.fromFn(lambda, environment, reducer) {
             | Ok(r) => Ok(r->Wrappers.sampleSet->Wrappers.evDistribution)
-            | Error(e) => e->Reducer_ErrorValue.REOperationError->Error
+            | Error(e) => e->SqError.Message.REOperationError->Error
             }
           | _ => Error(impossibleError)
           },
@@ -290,7 +289,7 @@ module Comparison = {
     r
     ->E.R2.fmap(r => r->Wrappers.sampleSet->Wrappers.evDistribution)
     ->E.R2.errMap(e =>
-      e->DistributionTypes.Error.sampleErrorToDistErr->Reducer_ErrorValue.REDistributionError
+      e->DistributionTypes.Error.sampleErrorToDistErr->SqError.Message.REDistributionError
     )
 
   let mkBig = (name, withDist, withFloat) =>

packages/squiggle-lang/src/rescript/FR/FR_Scoring.res

@@ -6,7 +6,7 @@ let requiresNamespace = true
 let runScoring = (estimate, answer, prior, env) => {
   GenericDist.Score.logScore(~estimate, ~answer, ~prior, ~env)
   ->E.R2.fmap(FunctionRegistry_Helpers.Wrappers.evNumber)
-  ->E.R2.errMap(e => Reducer_ErrorValue.REDistributionError(e))
+  ->E.R2.errMap(e => SqError.Message.REDistributionError(e))
 }
 
 let library = [
@@ -30,15 +30,15 @@ let library = [
             ("prior", FRTypeDist),
           ]),
         ],
-        ~run=(inputs, environment, _) => {
+        ~run=(inputs, context, _) => {
           switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.threeArgs(
             inputs,
             ("estimate", "answer", "prior"),
           ) {
           | Ok([IEvDistribution(estimate), IEvDistribution(d), IEvDistribution(prior)]) =>
-            runScoring(estimate, Score_Dist(d), Some(prior), environment)
+            runScoring(estimate, Score_Dist(d), Some(prior), context.environment)
           | Ok([IEvDistribution(estimate), IEvNumber(d), IEvDistribution(prior)]) =>
-            runScoring(estimate, Score_Scalar(d), Some(prior), environment)
+            runScoring(estimate, Score_Scalar(d), Some(prior), context.environment)
           | Error(e) => Error(e->FunctionRegistry_Helpers.wrapError)
           | _ => Error(FunctionRegistry_Helpers.impossibleError)
           }
@@ -48,15 +48,15 @@ let library = [
       FnDefinition.make(
         ~name="logScore",
         ~inputs=[FRTypeRecord([("estimate", FRTypeDist), ("answer", FRTypeDistOrNumber)])],
-        ~run=(inputs, environment, _) => {
+        ~run=(inputs, context, _) => {
           switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.twoArgs(
             inputs,
             ("estimate", "answer"),
           ) {
           | Ok([IEvDistribution(estimate), IEvDistribution(d)]) =>
-            runScoring(estimate, Score_Dist(d), None, environment)
+            runScoring(estimate, Score_Dist(d), None, context.environment)
           | Ok([IEvDistribution(estimate), IEvNumber(d)]) =>
-            runScoring(estimate, Score_Scalar(d), None, environment)
+            runScoring(estimate, Score_Scalar(d), None, context.environment)
           | Error(e) => Error(e->FunctionRegistry_Helpers.wrapError)
           | _ => Error(FunctionRegistry_Helpers.impossibleError)
           }
@@ -76,10 +76,10 @@ let library = [
       FnDefinition.make(
         ~name="klDivergence",
         ~inputs=[FRTypeDist, FRTypeDist],
-        ~run=(inputs, environment, _) => {
+        ~run=(inputs, context, _) => {
           switch inputs {
           | [IEvDistribution(estimate), IEvDistribution(d)] =>
-            runScoring(estimate, Score_Dist(d), None, environment)
+            runScoring(estimate, Score_Dist(d), None, context.environment)
           | _ => Error(FunctionRegistry_Helpers.impossibleError)
           }
         },

packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res

@@ -1,6 +1,7 @@
 @genType type reducerProject = ReducerProject_T.project //re-export
 
-type reducerErrorValue = ForTS_Reducer_ErrorValue.reducerErrorValue //use
+type error = SqError.t //use
+type errorMessage = SqError.Message.t //use
 
 type squiggleValue = ForTS_SquiggleValue.squiggleValue //use
 type squiggleValue_Record = ForTS_SquiggleValue.squiggleValue_Record //use
@@ -103,10 +104,8 @@ let cleanAllResults = (project: reducerProject): unit => project->Private.cleanA
 To set the includes one first has to call "parseIncludes". The parsed includes or the parser error is returned.
 */
 @genType
-let getIncludes = (project: reducerProject, sourceId: string): result<
+let getIncludes = (project: reducerProject, sourceId: string): result<array<string>, error> =>
-  array<string>,
+  project->Private.getIncludes(sourceId)
-  reducerErrorValue,
-> => project->Private.getIncludes(sourceId)
 
 /* Other sources contributing to the global namespace of this source. */
 @genType
@@ -198,10 +197,8 @@ let getBindings = (project: reducerProject, sourceId: string): squiggleValue_Rec
 Get the result after running this source file or the project
 */
 @genType
-let getResult = (project: reducerProject, sourceId: string): result<
+let getResult = (project: reducerProject, sourceId: string): result<squiggleValue, error> =>
-  squiggleValue,
+  project->Private.getResult(sourceId)
-  reducerErrorValue,
-> => project->Private.getResult(sourceId)
 
 /*
 This is a convenience function to get the result of a single source without creating a project. 
@@ -209,10 +206,8 @@ However, without a project, you cannot handle include directives.
 The source has to be include free
 */
 @genType
-let evaluate = (sourceCode: string): (
+let evaluate = (sourceCode: string): (result<squiggleValue, error>, squiggleValue_Record) =>
-  result<squiggleValue, reducerErrorValue>,
+  Private.evaluate(sourceCode)
-  squiggleValue_Record,
-) => Private.evaluate(sourceCode)
 
 @genType
 let setEnvironment = (project: reducerProject, environment: environment): unit =>
@@ -220,24 +215,3 @@ let setEnvironment = (project: reducerProject, environment: environment): unit =
 
 @genType
 let getEnvironment = (project: reducerProject): environment => project->Private.getEnvironment
-
-/*
-Foreign function interface is intentionally demolished.
-There is another way to do that: Umur.
-Also there is no more conversion from javascript to squiggle values currently.
-If the conversion to the new project is too difficult, I can add it later.
-*/
-
-// let foreignFunctionInterface = (
-//   lambdaValue: squiggleValue_Lambda,
-//   argArray: array<squiggleValue>,
-//   environment: environment,
-// ): result<squiggleValue, reducerErrorValue> => {
-//   let accessors = ReducerProject_ProjectAccessors_T.identityAccessorsWithEnvironment(environment)
-//   Reducer_Expression_Lambda.foreignFunctionInterface(
-//     lambdaValue,
-//     argArray,
-//     accessors,
-//     Reducer_Expression.reduceExpressionInProject,
-//   )
-// }

packages/squiggle-lang/src/rescript/ForTS/ForTS_Reducer_ErrorValue.res

@@ -1,18 +0,0 @@
-@genType type reducerErrorValue = Reducer_ErrorValue.errorValue //alias
-@genType type syntaxErrorLocation = Reducer_ErrorValue.syntaxErrorLocation //alias
-
-@genType
-let toString = (e: reducerErrorValue): string => Reducer_ErrorValue.errorToString(e)
-
-@genType
-let getLocation = (e: reducerErrorValue): option<syntaxErrorLocation> =>
-  switch e {
-  | RESyntaxError(_, optionalLocation) => optionalLocation
-  | _ => None
-  }
-
-@genType
-let createTodoError = (v: string) => Reducer_ErrorValue.RETodo(v)
-
-@genType
-let createOtherError = (v: string) => Reducer_ErrorValue.REOther(v)

packages/squiggle-lang/src/rescript/ForTS/ForTS_SquiggleValue/ForTS_SquiggleValue.res

@@ -1,5 +1,5 @@
 @genType type squiggleValue = Reducer_T.value //re-export
-type reducerErrorValue = ForTS_Reducer_ErrorValue.reducerErrorValue //use
+type error = SqError.t //use
 
 @genType type squiggleValue_Array = Reducer_T.arrayValue //re-export recursive type
 @genType type squiggleValue_Record = Reducer_T.map //re-export recursive type
@@ -69,7 +69,7 @@ let toString = (variant: squiggleValue) => Reducer_Value.toString(variant)
 // This is a useful method for unit tests.
 // Convert the result along with the error message to a string.
 @genType
-let toStringResult = (variantResult: result<squiggleValue, reducerErrorValue>) =>
+let toStringResult = (variantResult: result<squiggleValue, error>) =>
   Reducer_Value.toStringResult(variantResult)
 
 @genType

packages/squiggle-lang/src/rescript/ForTS/ForTS_SquiggleValue/ForTS_SquiggleValue_Lambda.res

@@ -1,9 +1,7 @@
 @genType type squiggleValue_Lambda = Reducer_T.lambdaValue //re-export
 
 @genType
-let toString = (v: squiggleValue_Lambda): string => Reducer_Value.toStringFunction(v)
+let toString = (v: squiggleValue_Lambda): string => Reducer_Value.toStringLambda(v)
 
 @genType
-let parameters = (v: squiggleValue_Lambda): array<string> => {
+let parameters = (v: squiggleValue_Lambda): array<string> => Reducer_Lambda.parameters(v)
-  v.parameters
-}

packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res

@@ -1,6 +1,3 @@
-@genType type reducerErrorValue = ForTS_Reducer_ErrorValue.reducerErrorValue //re-export
-@genType type syntaxErrorLocation = ForTS_Reducer_ErrorValue.syntaxErrorLocation //re-export
-
 @genType type reducerProject = ForTS_ReducerProject.reducerProject //re-export
 @genType type squiggleValue = ForTS_SquiggleValue.squiggleValue //re-export
 @genType type squiggleValue_Array = ForTS_SquiggleValue_Array.squiggleValue_Array //re-export

packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res

@@ -1,5 +1,5 @@
 type internalExpressionValueType = Reducer_Value.internalExpressionValueType
-type errorValue = Reducer_ErrorValue.errorValue
+type errorMessage = SqError.Message.t
 
 /*
   Function Registry "Type". A type, without any other information.
@@ -30,9 +30,9 @@ type fnDefinition = {
   inputs: array<frType>,
   run: (
     array<Reducer_T.value>,
-    Reducer_T.environment,
+    Reducer_T.context,
     Reducer_T.reducerFn,
-  ) => result<Reducer_T.value, errorValue>,
+  ) => result<Reducer_T.value, errorMessage>,
 }
 
 type function = {
@@ -122,11 +122,11 @@ module FnDefinition = {
   let run = (
     t: t,
     args: array<Reducer_T.value>,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
   ) => {
     switch t->isMatch(args) {
-    | true => t.run(args, env, reducer)
+    | true => t.run(args, context, reducer)
     | false => REOther("Incorrect Types")->Error
     }
   }
@@ -164,7 +164,7 @@ module Function = {
     nameSpace: nameSpace,
     definitions: definitions,
     output: output,
-    examples: examples |> E.O.default([]),
+    examples: examples->E.O2.default([]),
     isExperimental: isExperimental,
     requiresNamespace: requiresNamespace,
     description: description,
@@ -225,9 +225,9 @@ module Registry = {
     registry,
     fnName: string,
     args: array<Reducer_T.value>,
-    env: Reducer_T.environment,
+    context: Reducer_T.context,
     reducer: Reducer_T.reducerFn,
-  ): result<Reducer_T.value, errorValue> => {
+  ): result<Reducer_T.value, errorMessage> => {
     switch Belt.Map.String.get(registry.fnNameDict, fnName) {
     | Some(definitions) => {
         let showNameMatchDefinitions = () => {
@@ -241,7 +241,7 @@ module Registry = {
 
         let match = definitions->Js.Array2.find(def => def->FnDefinition.isMatch(args))
         switch match {
-        | Some(def) => def->FnDefinition.run(args, env, reducer)
+        | Some(def) => def->FnDefinition.run(args, context, reducer)
         | None => REOther(showNameMatchDefinitions())->Error
         }
       }

packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Helpers.res

@@ -2,8 +2,8 @@ open FunctionRegistry_Core
 open Reducer_T
 
 let impossibleErrorString = "Wrong inputs / Logically impossible"
-let impossibleError: errorValue = impossibleErrorString->Reducer_ErrorValue.REOther
+let impossibleError: errorMessage = impossibleErrorString->SqError.Message.REOther
-let wrapError = e => Reducer_ErrorValue.REOther(e)
+let wrapError = e => SqError.Message.REOther(e)
 
 module Wrappers = {
   let symbolic = r => DistributionTypes.Symbolic(r)

packages/squiggle-lang/src/rescript/Reducer/Reducer_Context.res

@@ -4,9 +4,13 @@ let defaultEnvironment: Reducer_T.environment = DistributionOperation.defaultEnv
 
 let createContext = (stdLib: Reducer_Namespace.t, environment: Reducer_T.environment): t => {
   {
+    frameStack: list{},
     bindings: stdLib->Reducer_Bindings.fromNamespace->Reducer_Bindings.extend,
     environment: environment,
+    inFunction: None,
   }
 }
 
-let createDefaultContext = (): t => createContext(SquiggleLibrary_StdLib.stdLib, defaultEnvironment)
+let currentFunctionName = (t: t): string => {
+  t.inFunction->E.O2.fmap(Reducer_Lambda_T.name)->E.O2.default(Reducer_T.topFrameName)
+}

packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_ChainPiece.res

@@ -1,27 +0,0 @@
-// types are disabled until review and rewrite for 0.5 interpreter compatibility
-/*
-module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
-module T = Reducer_Dispatch_T
-module TypeChecker = Reducer_Type_TypeChecker
-open Reducer_Value
-
-type errorValue = Reducer_ErrorValue.errorValue
-
-let makeFromTypes = jumpTable => {
-  let dispatchChainPiece: T.dispatchChainPiece = (
-    (fnName, fnArgs): functionCall,
-    accessors: ProjectAccessorsT.t,
-  ) => {
-    let jumpTableEntry = jumpTable->Js.Array2.find(elem => {
-      let (candidName, candidType, _) = elem
-      candidName == fnName && TypeChecker.checkITypeArgumentsBool(candidType, fnArgs)
-    })
-    switch jumpTableEntry {
-    | Some((_, _, bridgeFn)) => bridgeFn(fnArgs, accessors)->Some
-    | _ => None
-    }
-  }
-  dispatchChainPiece
-}
-
-*/

packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_T.res

@@ -1,21 +0,0 @@
-// module ExpressionT = Reducer_Expression_T
-// module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
-
-// // Each piece of the dispatch chain computes the result or returns None so that the chain can continue
-// type dispatchChainPiece = (
-//   Reducer_Value.functionCall,
-//   ProjectAccessorsT.t,
-// ) => option<result<Reducer_T.value, Reducer_ErrorValue.errorValue>>
-
-// type dispatchChainPieceWithReducer = (
-//   Reducer_Value.functionCall,
-//   ProjectAccessorsT.t,
-//   Reducer_T.reducerFn,
-// ) => option<result<Reducer_T.value, Reducer_ErrorValue.errorValue>>
-
-// // This is a switch statement case implementation: get the arguments and compute the result
-// type genericIEvFunction = (
-//   array<Reducer_T.value>,
-//   ProjectAccessorsT.t,
-// ) => result<Reducer_T.value, Reducer_ErrorValue.errorValue>
-

packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res

@@ -1,83 +0,0 @@
-//TODO: Do not export here but in ForTS__Types
-@gentype.import("peggy") @genType.as("LocationRange")
-type syntaxErrorLocation
-
-@genType.opaque
-type errorValue =
-  | REArityError(option<string>, int, int)
-  | REArrayIndexNotFound(string, int)
-  | REAssignmentExpected
-  | REDistributionError(DistributionTypes.error)
-  | REExpectedType(string, string)
-  | REExpressionExpected
-  | REFunctionExpected(string)
-  | REFunctionNotFound(string)
-  | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
-  | REMacroNotFound(string)
-  | RENotAFunction(string)
-  | REOperationError(Operation.operationError)
-  | RERecordPropertyNotFound(string, string)
-  | RESymbolNotFound(string)
-  | RESyntaxError(string, option<syntaxErrorLocation>)
-  | RETodo(string) // To do
-  | REUnitNotFound(string)
-  | RENeedToRun
-  | REOther(string)
-
-type t = errorValue
-
-exception ErrorException(errorValue)
-
-let errorToString = err =>
-  switch err {
-  | REArityError(_oFnName, arity, usedArity) =>
-    `${Js.String.make(arity)} arguments expected. Instead ${Js.String.make(
-        usedArity,
-      )} argument(s) were passed.`
-  | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
-  | REAssignmentExpected => "Assignment expected"
-  | REExpressionExpected => "Expression expected"
-  | REFunctionExpected(msg) => `Function expected: ${msg}`
-  | REFunctionNotFound(msg) => `Function not found: ${msg}`
-  | REDistributionError(err) => `Distribution Math Error: ${DistributionTypes.Error.toString(err)}`
-  | REOperationError(err) => `Math Error: ${Operation.Error.toString(err)}`
-  | REJavaScriptExn(omsg, oname) => {
-      let answer = "JS Exception:"
-      let answer = switch oname {
-      | Some(name) => `${answer} ${name}`
-      | _ => answer
-      }
-      let answer = switch omsg {
-      | Some(msg) => `${answer}: ${msg}`
-      | _ => answer
-      }
-      answer
-    }
-  | REMacroNotFound(macro) => `Macro not found: ${macro}`
-  | RENotAFunction(valueString) => `${valueString} is not a function`
-  | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
-  | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
-  | RESyntaxError(desc, _) => `Syntax Error: ${desc}`
-  | RETodo(msg) => `TODO: ${msg}`
-  | REExpectedType(typeName, valueString) => `Expected type: ${typeName} but got: ${valueString}`
-  | REUnitNotFound(unitName) => `Unit not found: ${unitName}`
-  | RENeedToRun => "Need to run"
-  | REOther(msg) => `Error: ${msg}`
-  }
-
-let fromException = exn =>
-  switch exn {
-  | ErrorException(e) => e
-  | Js.Exn.Error(e) =>
-    switch Js.Exn.message(e) {
-    | Some(message) => REOther(message)
-    | None =>
-      switch Js.Exn.name(e) {
-      | Some(name) => REOther(name)
-      | None => REOther("Unknown error")
-      }
-    }
-  | _e => REOther("Unknown error")
-  }
-
-let toException = (errorValue: t) => raise(ErrorException(errorValue))

packages/squiggle-lang/src/rescript/Reducer/Reducer_Exception.res

@@ -1,3 +0,0 @@
-// There are switch statement cases in the code which are impossible to reach by design.
-// ImpossibleException is a sign of programming error.
-exception ImpossibleException(string)

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res

@@ -1,16 +1,25 @@
 module Bindings = Reducer_Bindings
-module Lambda = Reducer_Expression_Lambda
 module Result = Belt.Result
 module T = Reducer_T
 
-type errorValue = Reducer_ErrorValue.errorValue
+let toLocation = (expression: T.expression): Reducer_Peggy_Parse.location => {
+  expression.ast.location
+}
+
+let throwFrom = (error: SqError.Message.t, expression: T.expression, context: T.context) =>
+  error->SqError.throwMessageWithFrameStack(
+    context.frameStack->Reducer_FrameStack.extend(
+      context->Reducer_Context.currentFunctionName,
+      Some(expression->toLocation),
+    ),
+  )
 
 /*
   Recursively evaluate the expression
 */
 let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
   // Js.log(`reduce: ${expression->Reducer_Expression_T.toString}`)
-  switch expression {
+  switch expression.content {
   | T.EBlock(statements) => {
       let innerContext = {...context, bindings: context.bindings->Bindings.extend}
       let (value, _) =
@@ -49,7 +58,7 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
           let (key, _) = eKey->evaluate(context)
           let keyString = switch key {
           | IEvString(s) => s
-          | _ => REOther("Record keys must be strings")->Reducer_ErrorValue.ErrorException->raise
+          | _ => REOther("Record keys must be strings")->throwFrom(expression, context)
           }
           let (value, _) = eValue->evaluate(context)
           (keyString, value)
@@ -73,7 +82,7 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
   | T.ESymbol(name) =>
     switch context.bindings->Bindings.get(name) {
     | Some(v) => (v, context)
-    | None => Reducer_ErrorValue.RESymbolNotFound(name)->Reducer_ErrorValue.ErrorException->raise
+    | None => RESymbolNotFound(name)->throwFrom(expression, context)
     }
 
   | T.EValue(value) => (value, context)
@@ -82,28 +91,39 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
       let (predicateResult, _) = predicate->evaluate(context)
       switch predicateResult {
       | T.IEvBool(value) => (value ? trueCase : falseCase)->evaluate(context)
-      | _ => REExpectedType("Boolean", "")->Reducer_ErrorValue.ErrorException->raise
+      | _ => REExpectedType("Boolean", "")->throwFrom(expression, context)
       }
     }
 
-  | T.ELambda(parameters, body) => (
+  | T.ELambda(parameters, body, name) => (
-      Lambda.makeLambda(parameters, context.bindings, body)->T.IEvLambda,
+      Reducer_Lambda.makeLambda(
+        name,
+        parameters,
+        context.bindings,
+        body,
+        expression->toLocation,
+      )->T.IEvLambda,
       context,
     )
 
   | T.ECall(fn, args) => {
       let (lambda, _) = fn->evaluate(context)
-      let argValues = Js.Array2.map(args, arg => {
+      let argValues = Belt.Array.map(args, arg => {
         let (argValue, _) = arg->evaluate(context)
         argValue
       })
       switch lambda {
-      | T.IEvLambda(lambda) => (
+      | T.IEvLambda(lambda) => {
-          Lambda.doLambdaCall(lambda, argValues, context.environment, evaluate),
+          let result = Reducer_Lambda.doLambdaCallFrom(
+            lambda,
+            argValues,
             context,
+            evaluate,
+            Some(expression->toLocation), // we have to pass the location of a current expression here, to put it on frameStack
           )
-      | _ =>
+          (result, context)
-        RENotAFunction(lambda->Reducer_Value.toString)->Reducer_ErrorValue.ErrorException->raise
+        }
+      | _ => RENotAFunction(lambda->Reducer_Value.toString)->throwFrom(expression, context)
       }
     }
   }
@@ -112,19 +132,22 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
 module BackCompatible = {
   // Those methods are used to support the existing tests
   // If they are used outside limited testing context, error location reporting will fail
-  let parse = (peggyCode: string): result<T.expression, errorValue> =>
+  let parse = (peggyCode: string): result<T.expression, Reducer_Peggy_Parse.parseError> =>
-    peggyCode->Reducer_Peggy_Parse.parse->Result.map(Reducer_Peggy_ToExpression.fromNode)
+    peggyCode->Reducer_Peggy_Parse.parse("main")->Result.map(Reducer_Peggy_ToExpression.fromNode)
 
-  let evaluate = (expression: T.expression): result<T.value, errorValue> => {
+  let createDefaultContext = () =>
-    let context = Reducer_Context.createDefaultContext()
+    Reducer_Context.createContext(SquiggleLibrary_StdLib.stdLib, Reducer_Context.defaultEnvironment)
+
+  let evaluate = (expression: T.expression): result<T.value, SqError.t> => {
+    let context = createDefaultContext()
     try {
       let (value, _) = expression->evaluate(context)
       value->Ok
     } catch {
-    | exn => Reducer_ErrorValue.fromException(exn)->Error
+    | exn => exn->SqError.fromException->Error
     }
   }
 
-  let evaluateString = (peggyCode: string): result<T.value, errorValue> =>
+  let evaluateString = (peggyCode: string): result<T.value, SqError.t> =>
-    parse(peggyCode)->Result.flatMap(evaluate)
+    parse(peggyCode)->E.R2.errMap(e => e->SqError.fromParseError)->Result.flatMap(evaluate)
 }

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res

@@ -1,16 +1,19 @@
-module BErrorValue = Reducer_ErrorValue
 module T = Reducer_T
 
-type errorValue = BErrorValue.errorValue
 type expression = Reducer_T.expression
+type expressionContent = Reducer_T.expressionContent
 
-let eArray = (anArray: array<T.expression>) => anArray->T.EArray
+let eArray = (anArray: array<T.expression>): expressionContent => anArray->T.EArray
 
 let eBool = aBool => aBool->T.IEvBool->T.EValue
 
-let eCall = (fn: expression, args: array<expression>): expression => T.ECall(fn, args)
+let eCall = (fn: expression, args: array<expression>): expressionContent => T.ECall(fn, args)
 
-let eLambda = (parameters: array<string>, expr: expression) => T.ELambda(parameters, expr)
+let eLambda = (
+  parameters: array<string>,
+  expr: expression,
+  name: option<string>,
+): expressionContent => T.ELambda(parameters, expr, name)
 
 let eNumber = aNumber => aNumber->T.IEvNumber->T.EValue
 
@@ -18,13 +21,13 @@ let eRecord = (aMap: array<(T.expression, T.expression)>) => aMap->T.ERecord
 
 let eString = aString => aString->T.IEvString->T.EValue
 
-let eSymbol = (name: string): expression => T.ESymbol(name)
+let eSymbol = (name: string): expressionContent => T.ESymbol(name)
 
-let eBlock = (exprs: array<expression>): expression => T.EBlock(exprs)
+let eBlock = (exprs: array<expression>): expressionContent => T.EBlock(exprs)
 
-let eProgram = (exprs: array<expression>): expression => T.EProgram(exprs)
+let eProgram = (exprs: array<expression>): expressionContent => T.EProgram(exprs)
 
-let eLetStatement = (symbol: string, valueExpression: expression): expression => T.EAssign(
+let eLetStatement = (symbol: string, valueExpression: expression): expressionContent => T.EAssign(
   symbol,
   valueExpression,
 )
@@ -33,11 +36,8 @@ let eTernary = (
   predicate: expression,
   trueCase: expression,
   falseCase: expression,
-): expression => T.ETernary(predicate, trueCase, falseCase)
+): expressionContent => T.ETernary(predicate, trueCase, falseCase)
 
-let eIdentifier = (name: string): expression => name->T.ESymbol
+let eIdentifier = (name: string): expressionContent => name->T.ESymbol
 
-// let eTypeIdentifier = (name: string): expression =>
+let eVoid: expressionContent = T.IEvVoid->T.EValue
-//   name->T.IEvTypeIdentifier->T.EValue
-
-let eVoid: expression = T.IEvVoid->T.EValue

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res

@@ -1,60 +0,0 @@
-module ErrorValue = Reducer_ErrorValue
-
-let doLambdaCall = (
-  lambdaValue: Reducer_T.lambdaValue,
-  args,
-  environment: Reducer_T.environment,
-  reducer: Reducer_T.reducerFn,
-): Reducer_T.value => {
-  lambdaValue.body(args, environment, reducer)
-}
-
-let makeLambda = (
-  parameters: array<string>,
-  bindings: Reducer_T.bindings,
-  body: Reducer_T.expression,
-): Reducer_T.lambdaValue => {
-  // TODO - clone bindings to avoid later redefinitions affecting lambdas?
-
-  // Note: with this implementation, FFI lambdas (created by other methods than calling `makeLambda`) are allowed to violate the rules, pollute the bindings, etc.
-  // Not sure yet if that's a bug or a feature.
-  // FunctionRegistry functions are unaffected by this, their API is too limited.
-
-  let lambda = (
-    arguments: array<Reducer_T.value>,
-    environment: Reducer_T.environment,
-    reducer: Reducer_T.reducerFn,
-  ) => {
-    let argsLength = arguments->Js.Array2.length
-    let parametersLength = parameters->Js.Array2.length
-    if argsLength !== parametersLength {
-      ErrorValue.REArityError(None, parametersLength, argsLength)->ErrorValue.ErrorException->raise
-    }
-
-    let localBindings = bindings->Reducer_Bindings.extend
-    let localBindingsWithParameters = parameters->Belt.Array.reduceWithIndex(localBindings, (
-      currentBindings,
-      parameter,
-      index,
-    ) => {
-      currentBindings->Reducer_Bindings.set(parameter, arguments[index])
-    })
-
-    let (value, _) = reducer(
-      body,
-      {bindings: localBindingsWithParameters, environment: environment},
-    )
-    value
-  }
-
-  {
-    // context: bindings,
-    body: lambda,
-    parameters: parameters,
-  }
-}
-
-let makeFFILambda = (body: Reducer_T.lambdaBody): Reducer_T.lambdaValue => {
-  body: body,
-  parameters: ["..."],
-}

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res

@@ -12,7 +12,7 @@ let semicolonJoin = values =>
   Converts the expression to String
 */
 let rec toString = (expression: t) =>
-  switch expression {
+  switch expression.content {
   | EBlock(statements) =>
     `{${Js.Array2.map(statements, aValue => toString(aValue))->semicolonJoin}}`
   | EProgram(statements) => Js.Array2.map(statements, aValue => toString(aValue))->semicolonJoin
@@ -24,37 +24,23 @@ let rec toString = (expression: t) =>
     `${predicate->toString} ? (${trueCase->toString}) : (${falseCase->toString})`
   | EAssign(name, value) => `${name} = ${value->toString}`
   | ECall(fn, args) => `(${fn->toString})(${args->Js.Array2.map(toString)->commaJoin})`
-  | ELambda(parameters, body) => `{|${parameters->commaJoin}| ${body->toString}}`
+  | ELambda(parameters, body, _) => `{|${parameters->commaJoin}| ${body->toString}}`
   | EValue(aValue) => Reducer_Value.toString(aValue)
   }
 
 let toStringResult = codeResult =>
   switch codeResult {
   | Ok(a) => `Ok(${toString(a)})`
-  | Error(m) => `Error(${Reducer_ErrorValue.errorToString(m)})`
+  | Error(m) => `Error(${Reducer_Peggy_Parse.toStringError(m)})`
   }
 
 let toStringResultOkless = codeResult =>
   switch codeResult {
   | Ok(a) => toString(a)
-  | Error(m) => `Error(${Reducer_ErrorValue.errorToString(m)})`
+  | Error(m) => `Error(${Reducer_Peggy_Parse.toStringError(m)})`
   }
 
 let inspect = (expr: t): t => {
   Js.log(toString(expr))
   expr
 }
-
-let inspectResult = (r: result<t, Reducer_ErrorValue.errorValue>): result<
-  t,
-  Reducer_ErrorValue.errorValue,
-> => {
-  Js.log(toStringResult(r))
-  r
-}
-
-let resultToValue = (rExpression: result<t, Reducer_ErrorValue.t>): t =>
-  switch rExpression {
-  | Ok(expression) => expression
-  | Error(errorValue) => Reducer_ErrorValue.toException(errorValue)
-  }

packages/squiggle-lang/src/rescript/Reducer/Reducer_FrameStack.res

@@ -0,0 +1,51 @@
+// This is called "frameStack" and not "callStack", because the last frame in errors is often not a function call.
+// A "frame" is a pair of a scope (function or top-level scope, currently stored as a string) and a location inside it.
+// See this comment to deconfuse about what a frame is: https://github.com/quantified-uncertainty/squiggle/pull/1172#issuecomment-1264115038
+type t = Reducer_T.frameStack
+
+module Frame = {
+  let toString = ({name, location}: Reducer_T.frame) =>
+    name ++
+    switch location {
+    | Some(location) =>
+      ` at line ${location.start.line->Js.Int.toString}, column ${location.start.column->Js.Int.toString}` // TODO - source id?
+    | None => ""
+    }
+
+  @genType
+  let getLocation = (t: Reducer_T.frame): option<Reducer_Peggy_Parse.location> => t.location
+
+  @genType
+  let getName = (t: Reducer_T.frame): string => t.name
+}
+
+let make = (): t => list{}
+
+let extend = (t: t, name: string, location: option<Reducer_Peggy_Parse.location>) =>
+  t->Belt.List.add({
+    name: name,
+    location: location,
+  })
+
+// this is useful for SyntaxErrors
+let makeSingleFrameStack = (location: Reducer_Peggy_Parse.location): t =>
+  make()->extend(Reducer_T.topFrameName, Some(location))
+
+// this includes the left offset because it's mostly used in SqError.toStringWithStackTrace
+let toString = (t: t) =>
+  t
+  ->Belt.List.map(s => "  " ++ s->Frame.toString ++ "\n")
+  ->Belt.List.toArray
+  ->Js.Array2.joinWith("")
+
+@genType
+let toFrameArray = (t: t): array<Reducer_T.frame> => t->Belt.List.toArray
+
+@genType
+let getTopFrame = (t: t): option<Reducer_T.frame> => t->Belt.List.head
+
+let isEmpty = (t: t): bool =>
+  switch t->Belt.List.head {
+  | Some(_) => true
+  | None => false
+  }

packages/squiggle-lang/src/rescript/Reducer/Reducer_Lambda.res

@@ -0,0 +1,95 @@
+type t = Reducer_T.lambdaValue
+
+// user-defined functions, i.e. `add2 = {|x, y| x + y}`, are built by this method
+let makeLambda = (
+  name: option<string>,
+  parameters: array<string>,
+  bindings: Reducer_T.bindings,
+  body: Reducer_T.expression,
+  location: Reducer_Peggy_Parse.location,
+): t => {
+  let lambda = (
+    arguments: array<Reducer_T.value>,
+    context: Reducer_T.context,
+    reducer: Reducer_T.reducerFn,
+  ) => {
+    let argsLength = arguments->E.A.length
+    let parametersLength = parameters->E.A.length
+    if argsLength !== parametersLength {
+      SqError.Message.REArityError(None, parametersLength, argsLength)->SqError.Message.throw
+    }
+
+    // create new bindings scope - technically not necessary, since bindings are immutable, but might help with debugging/new features in the future
+    let localBindings = bindings->Reducer_Bindings.extend
+
+    let localBindingsWithParameters = parameters->Belt.Array.reduceWithIndex(localBindings, (
+      currentBindings,
+      parameter,
+      index,
+    ) => {
+      currentBindings->Reducer_Bindings.set(parameter, arguments[index])
+    })
+
+    let lambdaContext: Reducer_T.context = {
+      bindings: localBindingsWithParameters, // based on bindings at the moment of lambda creation
+      environment: context.environment, // environment at the moment when lambda is called
+      frameStack: context.frameStack, // already extended in `doLambdaCall`
+      inFunction: context.inFunction, // already updated in `doLambdaCall`
+    }
+
+    let (value, _) = reducer(body, lambdaContext)
+    value
+  }
+
+  FnLambda({
+    // context: bindings,
+    name: name,
+    body: lambda,
+    parameters: parameters,
+    location: location,
+  })
+}
+
+// stdlib functions (everything in FunctionRegistry) are built by this method. Body is generated in SquiggleLibrary_StdLib.res
+let makeFFILambda = (name: string, body: Reducer_T.lambdaBody): t => FnBuiltin({
+  // Note: current bindings could be accidentally exposed here through context (compare with native lambda implementation above, where we override them with local bindings).
+  // But FunctionRegistry API is too limited for that to matter. Please take care not to violate that in the future by accident.
+  body: body,
+  name: name,
+})
+
+// this function doesn't scale to FunctionRegistry's polymorphic functions
+let parameters = (t: t): array<string> => {
+  switch t {
+  | FnLambda({parameters}) => parameters
+  | FnBuiltin(_) => ["..."]
+  }
+}
+
+let doLambdaCallFrom = (
+  t: t,
+  args: array<Reducer_T.value>,
+  context: Reducer_T.context,
+  reducer,
+  location: option<Reducer_Peggy_Parse.location>,
+) => {
+  let newContext = {
+    ...context,
+    frameStack: context.frameStack->Reducer_FrameStack.extend(
+      context->Reducer_Context.currentFunctionName,
+      location,
+    ),
+    inFunction: Some(t),
+  }
+
+  SqError.rethrowWithFrameStack(() => {
+    switch t {
+    | FnLambda({body}) => body(args, newContext, reducer)
+    | FnBuiltin({body}) => body(args, newContext, reducer)
+    }
+  }, newContext.frameStack)
+}
+
+let doLambdaCall = (t: t, args, context, reducer) => {
+  doLambdaCallFrom(t, args, context, reducer, None)
+}

packages/squiggle-lang/src/rescript/Reducer/Reducer_Lambda_T.res

@@ -0,0 +1,8 @@
+type t = Reducer_T.lambdaValue
+
+let name = (t: t): string => {
+  switch t {
+  | FnLambda({name}) => name->E.O2.default("<anonymous>")
+  | FnBuiltin({name}) => name
+  }
+}

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_GeneratedParser.peggy

@@ -7,26 +7,26 @@
 start
   = _nl start:outerBlock _nl finalComment?  {return start}
 
-zeroOMoreArgumentsBlockOrExpression = innerBlockOrExpression / lambda
+zeroOMoreArgumentsBlockOrExpression = lambda / innerBlockOrExpression
 
 outerBlock 
   = statements:array_statements  finalExpression: (statementSeparator @expression)?
     { if (finalExpression) statements.push(finalExpression)
-      return h.nodeProgram(statements) }
+      return h.nodeProgram(statements, location()) }
   / finalExpression: expression
-    { return h.nodeProgram([finalExpression]) }
+    { return h.nodeProgram([finalExpression], location()) }
     
 innerBlockOrExpression  
   = quotedInnerBlock
   / finalExpression: expression
-    { return h.nodeBlock([finalExpression])}
+    { return h.nodeBlock([finalExpression], location())}
 
 quotedInnerBlock  
   = '{' _nl statements:array_statements  finalExpression: (statementSeparator @expression)  _nl '}'
       { if (finalExpression) statements.push(finalExpression)
-        return h.nodeBlock(statements) }
+        return h.nodeBlock(statements, location()) }
   / '{' _nl finalExpression: expression  _nl '}'
-      { return h.nodeBlock([finalExpression]) }
+      { return h.nodeBlock([finalExpression], location()) }
 
 array_statements
   = head:statement tail:(statementSeparator @array_statements )
@@ -42,16 +42,16 @@ statement
 voidStatement 
   = "call" _nl value:zeroOMoreArgumentsBlockOrExpression
     { var variable = h.nodeIdentifier("_", location());
-      return h.nodeLetStatement(variable, value); }
+      return h.nodeLetStatement(variable, value, location()); }
 
 letStatement 
   = variable:variable _ assignmentOp _nl value:zeroOMoreArgumentsBlockOrExpression
-    { return h.nodeLetStatement(variable, value) }
+    { return h.nodeLetStatement(variable, value, location()) }
 
 defunStatement
   = variable:variable '(' _nl args:array_parameters _nl ')' _ assignmentOp _nl body:innerBlockOrExpression
-    { var value = h.nodeLambda(args, body)
+    { var value = h.nodeLambda(args, body, location(), variable)
-      return h.nodeLetStatement(variable, value) }
+      return h.nodeLetStatement(variable, value, location()) }
 
   assignmentOp "assignment" = '='
 
@@ -67,16 +67,16 @@ ifthenelse
   = 'if' __nl condition:logicalAdditive 
       __nl 'then' __nl trueExpression:innerBlockOrExpression 
     __nl 'else' __nl falseExpression:(ifthenelse/innerBlockOrExpression)
-    { return h.nodeTernary(condition, trueExpression, falseExpression) }
+    { return h.nodeTernary(condition, trueExpression, falseExpression, location()) }
   
 ternary 
   = condition:logicalAdditive _ '?' _nl trueExpression:logicalAdditive _ ':' _nl falseExpression:(ternary/logicalAdditive)
-    { return h.nodeTernary(condition, trueExpression, falseExpression) }
+    { return h.nodeTernary(condition, trueExpression, falseExpression, location()) }
 
 logicalAdditive
   = head:logicalMultiplicative tail:(_ operator:logicalAdditiveOp _nl arg:logicalMultiplicative {return {operator: operator, right: arg}})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right])
+      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right], location())
     }, head)}
 
   logicalAdditiveOp "operator" = '||'
@@ -85,21 +85,21 @@ logicalAdditive
 logicalMultiplicative
   = head:equality tail:(_ operator:logicalMultiplicativeOp _nl arg:equality {return {operator: operator, right: arg}})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right])
+      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right], location())
     }, head)}
 
   logicalMultiplicativeOp "operator" = '&&'
 
 equality
   = left:relational _ operator:equalityOp _nl right:relational 
-  { return h.makeFunctionCall(h.toFunction[operator], [left, right])}
+  { return h.makeFunctionCall(h.toFunction[operator], [left, right], location())}
   / relational  
   
   equalityOp "operator" = '=='/'!='
 
 relational
   = left:credibleInterval _ operator:relationalOp _nl right:credibleInterval 
-  { return h.makeFunctionCall(h.toFunction[operator], [left, right])}
+  { return h.makeFunctionCall(h.toFunction[operator], [left, right], location())}
   / credibleInterval
 
   relationalOp "operator" = '<='/'<'/'>='/'>'
@@ -107,7 +107,7 @@ relational
 credibleInterval
   = head:additive tail:(__ operator:credibleIntervalOp __nl arg:additive {return {operator: operator, right: arg}})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right])
+      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right], location())
     }, head)}
 
     credibleIntervalOp "operator" = 'to'
@@ -115,7 +115,7 @@ credibleInterval
 additive
   = head:multiplicative tail:(_ operator:additiveOp _nl arg:multiplicative {return {operator: operator, right: arg}})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right])
+      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right], location())
     }, head)}
 
   additiveOp "operator" = '+' / '-' / '.+' / '.-'
@@ -123,7 +123,7 @@ additive
 multiplicative
   = head:power tail:(_ operator:multiplicativeOp _nl arg:power {return {operator: operator, right: arg}})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right])
+      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right], location())
     }, head)}
 
   multiplicativeOp "operator" = '*' / '/' / '.*' / './'
@@ -131,7 +131,7 @@ multiplicative
 power
   = head:chainFunctionCall tail:(_ operator:powerOp _nl arg:chainFunctionCall {return {operator: operator, right: arg}})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right])
+      return h.makeFunctionCall(h.toFunction[element.operator], [result, element.right], location())
     }, head)}
 
   powerOp "operator" = '^' / '.^'
@@ -139,7 +139,7 @@ power
 chainFunctionCall
   = head:unary tail:(_ ('->'/'|>') _nl chained:chainedFunction {return chained})* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(element.fnName, [result, ...element.args])
+      return h.makeFunctionCall(element.fnName, [result, ...element.args], location())
     }, head)}
 
   chainedFunction
@@ -154,7 +154,7 @@ chainFunctionCall
 
 unary
   = unaryOperator:unaryOperator _nl right:(unary/postOperator)
-  { return h.makeFunctionCall(h.unaryToFunction[unaryOperator], [right])}
+  { return h.makeFunctionCall(h.unaryToFunction[unaryOperator], [right], location())}
   / postOperator
   
   unaryOperator "unary operator"
@@ -169,17 +169,17 @@ collectionElement
     tail:(
       _ '[' _nl arg:expression  _nl ']' {return {fn: h.postOperatorToFunction['[]'], args: [arg]}}
     / _ '(' _nl args:array_functionArguments  _nl ')' {return {fn: h.postOperatorToFunction['()'], args: args}}
-    / '.' arg:$dollarIdentifier {return {fn: h.postOperatorToFunction['[]'], args: [h.nodeString(arg)]}}
+    / '.' arg:$dollarIdentifier {return {fn: h.postOperatorToFunction['[]'], args: [h.nodeString(arg, location())]}}
     )* 
   { return tail.reduce(function(result, element) {
-      return h.makeFunctionCall(element.fn, [result, ...element.args])
+      return h.makeFunctionCall(element.fn, [result, ...element.args], location())
     }, head)}
 
     array_functionArguments 
       = head:expression tail:(_ ',' _nl @expression)* 
       { return [head, ...tail]; }
   / ""
-      {return [h.nodeVoid()];}
+      {return [h.nodeVoid(location())];}
 
 atom
   = '(' _nl expression:expression _nl ')' {return expression}
@@ -195,7 +195,7 @@ basicLiteral
   / voidLiteral
 
 voidLiteral 'void'
-  = "()" {return h.nodeVoid();}
+  = "()" {return h.nodeVoid(location());}
 
 variable = dollarIdentifierWithModule / dollarIdentifier
 
@@ -221,36 +221,36 @@ dollarIdentifier '$identifier'
   = ([\$_a-z]+[\$_a-z0-9]i*) {return h.nodeIdentifier(text(), location())} 
 
 moduleIdentifier 'identifier'
-  = ([A-Z]+[_a-z0-9]i*) {return h.nodeModuleIdentifier(text())} 
+  = ([A-Z]+[_a-z0-9]i*) {return h.nodeModuleIdentifier(text(), location())} 
 
 
 string 'string'
-  = characters:("'" @([^'])* "'") {return h.nodeString(characters.join(''))} 
+  = characters:("'" @([^'])* "'") {return h.nodeString(characters.join(''), location())} 
-  / characters:('"' @([^"])* '"') {return h.nodeString(characters.join(''))}
+  / characters:('"' @([^"])* '"') {return h.nodeString(characters.join(''), location())}
 
 number = number:(float / integer) unit:unitIdentifier?
   { 
     if (unit === null)
       { return number }
     else
-      { return h.makeFunctionCall('fromUnit_'+unit.value, [number]) 
+      { return h.makeFunctionCall('fromUnit_'+unit.value, [number], location()) 
       }
   }
 
 integer 'integer'
   = d+ !"\." ![e]i
-  { return h.nodeInteger(parseInt(text()))} 
+  { return h.nodeInteger(parseInt(text()), location())} 
   
 float 'float'
   = $(((d+ "\." d*) / ("\." d+)) floatExponent? / d+ floatExponent)
-  { return h.nodeFloat(parseFloat(text()))} 
+  { return h.nodeFloat(parseFloat(text()), location())} 
 
     floatExponent = [e]i '-'? d+
     d = [0-9]
     
 boolean 'boolean'
   = ('true'/'false')  ! [a-z]i ! [_$]
-  { return h.nodeBoolean(text() === 'true')}
+  { return h.nodeBoolean(text() === 'true', location())}
 
 valueConstructor
   = recordConstructor
@@ -261,15 +261,15 @@ valueConstructor
 lambda  
   = '{' _nl '|' _nl args:array_parameters _nl '|' _nl statements:array_statements  finalExpression: (statementSeparator @expression)  _nl '}'
       { statements.push(finalExpression) 
-        return h.nodeLambda(args, h.nodeBlock(statements)) }
+        return h.nodeLambda(args, h.nodeBlock(statements, location()), location(), undefined) }
   / '{' _nl '|' _nl args:array_parameters _nl '|' _nl finalExpression: expression  _nl '}'
-      { return h.nodeLambda(args, finalExpression) }
+      { return h.nodeLambda(args, finalExpression, location(), undefined) }
 
 arrayConstructor 'array'
   = '[' _nl ']'
-    { return h.constructArray([]); }
+    { return h.constructArray([], location()); }
   / '[' _nl args:array_elements _nl ']' 
-    { return h.constructArray(args); }
+    { return h.constructArray(args, location()); }
 
   array_elements 
     = head:expression tail:(_ ',' _nl @expression)* 
@@ -277,7 +277,7 @@ arrayConstructor 'array'
 
 recordConstructor  'record'
   = '{' _nl args:array_recordArguments _nl end_of_record
-  { return h.constructRecord(args); }
+  { return h.constructRecord(args, location()); }
 
   end_of_record 
     = '}'
@@ -289,7 +289,7 @@ recordConstructor  'record'
 
   keyValuePair 
     = key:expression _ ':' _nl value:expression 
-    { return h.nodeKeyValue(key, value)}
+    { return h.nodeKeyValue(key, value, location())}
 
 // Separators
 

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res

@@ -1,22 +1,37 @@
 module Extra = Reducer_Extra
-open Reducer_ErrorValue
 
-type node = {"type": string}
+@genType
+type locationPoint = {
+  line: int,
+  column: int,
+}
+@genType
+type location = {
+  source: string,
+  start: locationPoint,
+  end: locationPoint,
+}
 
-@module("./Reducer_Peggy_GeneratedParser.js") external parse__: string => node = "parse"
+type node = {"type": string, "location": location}
 
-type withLocation = {"location": Reducer_ErrorValue.syntaxErrorLocation}
+type parseError = SyntaxError(string, location)
+
+type parseResult = result<node, parseError>
+
+@module("./Reducer_Peggy_GeneratedParser.js")
+external parse__: (string, {"grammarSource": string}) => node = "parse"
+
+type withLocation = {"location": location}
 external castWithLocation: Js.Exn.t => withLocation = "%identity"
 
-let syntaxErrorToLocation = (error: Js.Exn.t): Reducer_ErrorValue.syntaxErrorLocation =>
+let syntaxErrorToLocation = (error: Js.Exn.t): location => castWithLocation(error)["location"]
-  castWithLocation(error)["location"]
 
-let parse = (expr: string): result<node, errorValue> =>
+let parse = (expr: string, source: string): parseResult =>
   try {
-    Ok(parse__(expr))
+    Ok(parse__(expr, {"grammarSource": source}))
   } catch {
   | Js.Exn.Error(obj) =>
-    RESyntaxError(Belt.Option.getExn(Js.Exn.message(obj)), syntaxErrorToLocation(obj)->Some)->Error
+    SyntaxError(Belt.Option.getExn(Js.Exn.message(obj)), syntaxErrorToLocation(obj))->Error
   }
 
 type nodeBlock = {...node, "statements": array<node>}
@@ -29,32 +44,35 @@ type nodeIdentifier = {...node, "value": string}
 type nodeInteger = {...node, "value": int}
 type nodeKeyValue = {...node, "key": node, "value": node}
 type nodeRecord = {...node, "elements": array<nodeKeyValue>}
-type nodeLambda = {...node, "args": array<nodeIdentifier>, "body": node}
+type nodeLambda = {...node, "args": array<nodeIdentifier>, "body": node, "name": option<string>}
 type nodeLetStatement = {...node, "variable": nodeIdentifier, "value": node}
 type nodeModuleIdentifier = {...node, "value": string}
 type nodeString = {...node, "value": string}
 type nodeTernary = {...node, "condition": node, "trueExpression": node, "falseExpression": node}
-// type nodeTypeIdentifier = {...node, "value": string}
 type nodeVoid = node
 
-type peggyNode =
+type astContent =
-  | PgNodeBlock(nodeBlock)
+  | ASTBlock(nodeBlock)
-  | PgNodeProgram(nodeProgram)
+  | ASTProgram(nodeProgram)
-  | PgNodeArray(nodeArray)
+  | ASTArray(nodeArray)
-  | PgNodeRecord(nodeRecord)
+  | ASTRecord(nodeRecord)
-  | PgNodeBoolean(nodeBoolean)
+  | ASTBoolean(nodeBoolean)
-  | PgNodeFloat(nodeFloat)
+  | ASTFloat(nodeFloat)
-  | PgNodeCall(nodeCall)
+  | ASTCall(nodeCall)
-  | PgNodeIdentifier(nodeIdentifier)
+  | ASTIdentifier(nodeIdentifier)
-  | PgNodeInteger(nodeInteger)
+  | ASTInteger(nodeInteger)
-  | PgNodeKeyValue(nodeKeyValue)
+  | ASTKeyValue(nodeKeyValue)
-  | PgNodeLambda(nodeLambda)
+  | ASTLambda(nodeLambda)
-  | PgNodeLetStatement(nodeLetStatement)
+  | ASTLetStatement(nodeLetStatement)
-  | PgNodeModuleIdentifier(nodeModuleIdentifier)
+  | ASTModuleIdentifier(nodeModuleIdentifier)
-  | PgNodeString(nodeString)
+  | ASTString(nodeString)
-  | PgNodeTernary(nodeTernary)
+  | ASTTernary(nodeTernary)
-  // | PgNodeTypeIdentifier(nodeTypeIdentifier)
+  | ASTVoid(nodeVoid)
-  | PgNodeVoid(nodeVoid)
+
+type ast = {
+  location: location,
+  content: astContent,
+}
 
 external castNodeBlock: node => nodeBlock = "%identity"
 external castNodeProgram: node => nodeProgram = "%identity"
@@ -71,80 +89,92 @@ external castNodeLetStatement: node => nodeLetStatement = "%identity"
 external castNodeModuleIdentifier: node => nodeModuleIdentifier = "%identity"
 external castNodeString: node => nodeString = "%identity"
 external castNodeTernary: node => nodeTernary = "%identity"
-// external castNodeTypeIdentifier: node => nodeTypeIdentifier = "%identity"
 external castNodeVoid: node => nodeVoid = "%identity"
 
 exception UnsupportedPeggyNodeType(string) // This should never happen; programming error
-let castNodeType = (node: node) =>
+let nodeToAST = (node: node) => {
-  switch node["type"] {
+  let content = switch node["type"] {
-  | "Block" => node->castNodeBlock->PgNodeBlock
+  | "Block" => node->castNodeBlock->ASTBlock
-  | "Program" => node->castNodeBlock->PgNodeProgram
+  | "Program" => node->castNodeBlock->ASTProgram
-  | "Array" => node->castNodeArray->PgNodeArray
+  | "Array" => node->castNodeArray->ASTArray
-  | "Record" => node->castNodeRecord->PgNodeRecord
+  | "Record" => node->castNodeRecord->ASTRecord
-  | "Boolean" => node->castNodeBoolean->PgNodeBoolean
+  | "Boolean" => node->castNodeBoolean->ASTBoolean
-  | "Call" => node->castNodeCall->PgNodeCall
+  | "Call" => node->castNodeCall->ASTCall
-  | "Float" => node->castNodeFloat->PgNodeFloat
+  | "Float" => node->castNodeFloat->ASTFloat
-  | "Identifier" => node->castNodeIdentifier->PgNodeIdentifier
+  | "Identifier" => node->castNodeIdentifier->ASTIdentifier
-  | "Integer" => node->castNodeInteger->PgNodeInteger
+  | "Integer" => node->castNodeInteger->ASTInteger
-  | "KeyValue" => node->castNodeKeyValue->PgNodeKeyValue
+  | "KeyValue" => node->castNodeKeyValue->ASTKeyValue
-  | "Lambda" => node->castNodeLambda->PgNodeLambda
+  | "Lambda" => node->castNodeLambda->ASTLambda
-  | "LetStatement" => node->castNodeLetStatement->PgNodeLetStatement
+  | "LetStatement" => node->castNodeLetStatement->ASTLetStatement
-  | "ModuleIdentifier" => node->castNodeModuleIdentifier->PgNodeModuleIdentifier
+  | "ModuleIdentifier" => node->castNodeModuleIdentifier->ASTModuleIdentifier
-  | "String" => node->castNodeString->PgNodeString
+  | "String" => node->castNodeString->ASTString
-  | "Ternary" => node->castNodeTernary->PgNodeTernary
+  | "Ternary" => node->castNodeTernary->ASTTernary
-  // | "TypeIdentifier" => node->castNodeTypeIdentifier->PgNodeTypeIdentifier
+  | "Void" => node->castNodeVoid->ASTVoid
-  | "Void" => node->castNodeVoid->PgNodeVoid
   | _ => raise(UnsupportedPeggyNodeType(node["type"]))
   }
 
-let rec pgToString = (peggyNode: peggyNode): string => {
+  {location: node["location"], content: content}
+}
+
+let nodeIdentifierToAST = (node: nodeIdentifier) => {
+  {location: node["location"], content: node->ASTIdentifier}
+}
+
+let nodeKeyValueToAST = (node: nodeKeyValue) => {
+  {location: node["location"], content: node->ASTKeyValue}
+}
+
+let rec pgToString = (ast: ast): string => {
   let argsToString = (args: array<nodeIdentifier>): string =>
-    args->Js.Array2.map(arg => PgNodeIdentifier(arg)->pgToString)->Js.Array2.toString
+    args->Belt.Array.map(arg => arg->nodeIdentifierToAST->pgToString)->Js.Array2.toString
 
   let nodesToStringUsingSeparator = (nodes: array<node>, separator: string): string =>
-    nodes->Js.Array2.map(toString)->Extra.Array.intersperse(separator)->Js.String.concatMany("")
+    nodes->Belt.Array.map(toString)->Extra.Array.intersperse(separator)->Js.String.concatMany("")
 
-  let pgNodesToStringUsingSeparator = (nodes: array<peggyNode>, separator: string): string =>
+  let pgNodesToStringUsingSeparator = (nodes: array<ast>, separator: string): string =>
-    nodes->Js.Array2.map(pgToString)->Extra.Array.intersperse(separator)->Js.String.concatMany("")
+    nodes->Belt.Array.map(pgToString)->Extra.Array.intersperse(separator)->Js.String.concatMany("")
 
-  switch peggyNode {
+  switch ast.content {
-  | PgNodeBlock(node)
+  | ASTBlock(node)
-  | PgNodeProgram(node) =>
+  | ASTProgram(node) =>
     "{" ++ node["statements"]->nodesToStringUsingSeparator("; ") ++ "}"
-  | PgNodeArray(node) => "[" ++ node["elements"]->nodesToStringUsingSeparator("; ") ++ "]"
+  | ASTArray(node) => "[" ++ node["elements"]->nodesToStringUsingSeparator("; ") ++ "]"
-  | PgNodeRecord(node) =>
+  | ASTRecord(node) =>
     "{" ++
     node["elements"]
-    ->Js.Array2.map(element => PgNodeKeyValue(element))
+    ->Belt.Array.map(element => element->nodeKeyValueToAST)
     ->pgNodesToStringUsingSeparator(", ") ++ "}"
-  | PgNodeBoolean(node) => node["value"]->Js.String.make
+  | ASTBoolean(node) => node["value"]->Js.String.make
-  | PgNodeCall(node) =>
+  | ASTCall(node) =>
     "(" ++ node["fn"]->toString ++ " " ++ node["args"]->nodesToStringUsingSeparator(" ") ++ ")"
-  | PgNodeFloat(node) => node["value"]->Js.String.make
+  | ASTFloat(node) => node["value"]->Js.String.make
-  | PgNodeIdentifier(node) => `:${node["value"]}`
+  | ASTIdentifier(node) => `:${node["value"]}`
-  | PgNodeInteger(node) => node["value"]->Js.String.make
+  | ASTInteger(node) => node["value"]->Js.String.make
-  | PgNodeKeyValue(node) => toString(node["key"]) ++ ": " ++ toString(node["value"])
+  | ASTKeyValue(node) => toString(node["key"]) ++ ": " ++ toString(node["value"])
-  | PgNodeLambda(node) =>
+  | ASTLambda(node) => "{|" ++ node["args"]->argsToString ++ "| " ++ node["body"]->toString ++ "}"
-    "{|" ++ node["args"]->argsToString ++ "| " ++ node["body"]->toString ++ "}"
+  | ASTLetStatement(node) =>
-  | PgNodeLetStatement(node) =>
+    pgToString(node["variable"]->nodeIdentifierToAST) ++ " = " ++ toString(node["value"])
-    pgToString(PgNodeIdentifier(node["variable"])) ++ " = " ++ toString(node["value"])
+  | ASTModuleIdentifier(node) => `@${node["value"]}`
-  | PgNodeModuleIdentifier(node) => `@${node["value"]}`
+  | ASTString(node) => `'${node["value"]->Js.String.make}'`
-  | PgNodeString(node) => `'${node["value"]->Js.String.make}'`
+  | ASTTernary(node) =>
-  | PgNodeTernary(node) =>
     "(::$$_ternary_$$ " ++
     toString(node["condition"]) ++
     " " ++
     toString(node["trueExpression"]) ++
     " " ++
     toString(node["falseExpression"]) ++ ")"
-  // | PgNodeTypeIdentifier(node) => `#${node["value"]}`
+  | ASTVoid(_node) => "()"
-  | PgNodeVoid(_node) => "()"
   }
 }
-and toString = (node: node): string => node->castNodeType->pgToString
+and toString = (node: node): string => node->nodeToAST->pgToString
 
-let toStringResult = (rNode: result<node, errorValue>): string =>
+let toStringError = (error: parseError): string => {
+  let SyntaxError(message, _) = error
+  `Syntax Error: ${message}}`
+}
+
+let toStringResult = (rNode: parseResult): string =>
   switch rNode {
-  | Ok(node) => toString(node)
+  | Ok(node) => node->toString
-  | Error(error) => `Error(${errorToString(error)})`
+  | Error(error) => `Error(${error->toStringError})`
   }

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_ToExpression.res

@@ -3,23 +3,27 @@ module ExpressionT = Reducer_Expression_T
 module Parse = Reducer_Peggy_Parse
 
 type expression = Reducer_T.expression
+type expressionContent = Reducer_T.expressionContent
 
 let rec fromNode = (node: Parse.node): expression => {
+  let ast = Parse.nodeToAST(node)
+
+  let content: expressionContent = {
     let caseBlock = nodeBlock =>
       ExpressionBuilder.eBlock(nodeBlock["statements"]->Js.Array2.map(fromNode))
 
     let caseProgram = nodeProgram =>
       ExpressionBuilder.eProgram(nodeProgram["statements"]->Js.Array2.map(fromNode))
 
-  let caseLambda = (nodeLambda: Parse.nodeLambda): expression => {
+    let caseLambda = (nodeLambda: Parse.nodeLambda): expressionContent => {
       let args =
         nodeLambda["args"]->Js.Array2.map((argNode: Parse.nodeIdentifier) => argNode["value"])
       let body = nodeLambda["body"]->fromNode
 
-    ExpressionBuilder.eLambda(args, body)
+      ExpressionBuilder.eLambda(args, body, nodeLambda["name"])
     }
 
-  let caseRecord = (nodeRecord): expression => {
+    let caseRecord = (nodeRecord): expressionContent => {
       nodeRecord["elements"]
       ->Js.Array2.map(keyValueNode => (
         keyValueNode["key"]->fromNode,
@@ -28,30 +32,30 @@ let rec fromNode = (node: Parse.node): expression => {
       ->ExpressionBuilder.eRecord
     }
 
-  switch Parse.castNodeType(node) {
+    switch ast.content {
-  | PgNodeBlock(nodeBlock) => caseBlock(nodeBlock)
+    | ASTBlock(nodeBlock) => caseBlock(nodeBlock)
-  | PgNodeProgram(nodeProgram) => caseProgram(nodeProgram)
+    | ASTProgram(nodeProgram) => caseProgram(nodeProgram)
-  | PgNodeArray(nodeArray) =>
+    | ASTArray(nodeArray) =>
       ExpressionBuilder.eArray(nodeArray["elements"]->Js.Array2.map(fromNode))
-  | PgNodeRecord(nodeRecord) => caseRecord(nodeRecord)
+    | ASTRecord(nodeRecord) => caseRecord(nodeRecord)
-  | PgNodeBoolean(nodeBoolean) => ExpressionBuilder.eBool(nodeBoolean["value"])
+    | ASTBoolean(nodeBoolean) => ExpressionBuilder.eBool(nodeBoolean["value"])
-  | PgNodeCall(nodeCall) =>
+    | ASTCall(nodeCall) =>
       ExpressionBuilder.eCall(fromNode(nodeCall["fn"]), nodeCall["args"]->Js.Array2.map(fromNode))
-  | PgNodeFloat(nodeFloat) => ExpressionBuilder.eNumber(nodeFloat["value"])
+    | ASTFloat(nodeFloat) => ExpressionBuilder.eNumber(nodeFloat["value"])
-  | PgNodeIdentifier(nodeIdentifier) => ExpressionBuilder.eSymbol(nodeIdentifier["value"])
+    | ASTIdentifier(nodeIdentifier) => ExpressionBuilder.eSymbol(nodeIdentifier["value"])
-  | PgNodeInteger(nodeInteger) => ExpressionBuilder.eNumber(Belt.Int.toFloat(nodeInteger["value"]))
+    | ASTInteger(nodeInteger) => ExpressionBuilder.eNumber(Belt.Int.toFloat(nodeInteger["value"]))
-  | PgNodeKeyValue(nodeKeyValue) =>
+    | ASTKeyValue(nodeKeyValue) =>
       ExpressionBuilder.eArray([fromNode(nodeKeyValue["key"]), fromNode(nodeKeyValue["value"])])
-  | PgNodeLambda(nodeLambda) => caseLambda(nodeLambda)
+    | ASTLambda(nodeLambda) => caseLambda(nodeLambda)
-  | PgNodeLetStatement(nodeLetStatement) =>
+    | ASTLetStatement(nodeLetStatement) =>
       ExpressionBuilder.eLetStatement(
         nodeLetStatement["variable"]["value"],
         fromNode(nodeLetStatement["value"]),
       )
-  | PgNodeModuleIdentifier(nodeModuleIdentifier) =>
+    | ASTModuleIdentifier(nodeModuleIdentifier) =>
       ExpressionBuilder.eIdentifier(nodeModuleIdentifier["value"])
-  | PgNodeString(nodeString) => ExpressionBuilder.eString(nodeString["value"])
+    | ASTString(nodeString) => ExpressionBuilder.eString(nodeString["value"])
-  | PgNodeTernary(nodeTernary) =>
+    | ASTTernary(nodeTernary) =>
       ExpressionBuilder.eTernary(
         fromNode(nodeTernary["condition"]),
         fromNode(nodeTernary["trueExpression"]),
@@ -59,6 +63,12 @@ let rec fromNode = (node: Parse.node): expression => {
       )
     // | PgNodeTypeIdentifier(nodeTypeIdentifier) =>
     //   ExpressionBuilder.eTypeIdentifier(nodeTypeIdentifier["value"])
-  | PgNodeVoid(_) => ExpressionBuilder.eVoid
+    | ASTVoid(_) => ExpressionBuilder.eVoid
+    }
+  }
+
+  {
+    ast: ast,
+    content: content,
   }
 }

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/helpers.ts

@@ -34,83 +34,92 @@ export const postOperatorToFunction = {
   "[]": "$_atIndex_$",
 };
 
-type NodeBlock = {
+type Node = {
+  location: LocationRange;
+};
+
+type NodeBlock = Node & {
   type: "Block";
   statements: AnyPeggyNode[];
 };
 
-type NodeProgram = {
+type NodeProgram = Node & {
   type: "Program";
   statements: AnyPeggyNode[];
 };
 
-type NodeArray = {
+type NodeArray = Node & {
   type: "Array";
   elements: AnyPeggyNode[];
 };
 
-type NodeRecord = {
+type NodeRecord = Node & {
   type: "Record";
   elements: NodeKeyValue[];
 };
 
-type NodeCall = {
+type NodeCall = Node & {
   type: "Call";
   fn: AnyPeggyNode;
   args: AnyPeggyNode[];
 };
 
-type NodeFloat = {
+type NodeFloat = Node & {
   type: "Float";
   value: number;
 };
 
-type NodeInteger = {
+type NodeInteger = Node & {
   type: "Integer";
   value: number;
 };
 
-type NodeIdentifier = {
+type NodeIdentifier = Node & {
   type: "Identifier";
   value: string;
 };
 
-type NodeLetStatement = {
+type NodeLetStatement = Node & {
   type: "LetStatement";
   variable: NodeIdentifier;
   value: AnyPeggyNode;
 };
 
-type NodeLambda = {
+type NodeLambda = Node & {
   type: "Lambda";
   args: AnyPeggyNode[];
   body: AnyPeggyNode;
+  name?: string;
 };
 
-type NodeTernary = {
+type NodeTernary = Node & {
   type: "Ternary";
   condition: AnyPeggyNode;
   trueExpression: AnyPeggyNode;
   falseExpression: AnyPeggyNode;
 };
 
-type NodeKeyValue = {
+type NodeKeyValue = Node & {
   type: "KeyValue";
   key: AnyPeggyNode;
   value: AnyPeggyNode;
 };
 
-type NodeString = {
+type NodeString = Node & {
   type: "String";
   value: string;
   location?: LocationRange;
 };
 
-type NodeBoolean = {
+type NodeBoolean = Node & {
   type: "Boolean";
   value: boolean;
 };
 
+type NodeVoid = Node & {
+  type: "Void";
+};
+
 export type AnyPeggyNode =
   | NodeArray
   | NodeRecord
@@ -125,47 +134,78 @@ export type AnyPeggyNode =
   | NodeTernary
   | NodeKeyValue
   | NodeString
-  | NodeBoolean;
+  | NodeBoolean
+  | NodeVoid;
 
-export function makeFunctionCall(fn: string, args: AnyPeggyNode[]) {
+export function makeFunctionCall(
+  fn: string,
+  args: AnyPeggyNode[],
+  location: LocationRange
+) {
   if (fn === "$$_applyAll_$$") {
-    return nodeCall(args[0], args.splice(1));
+    return nodeCall(args[0], args.splice(1), location);
   } else {
-    return nodeCall(nodeIdentifier(fn), args);
+    return nodeCall(nodeIdentifier(fn, location), args, location);
   }
 }
 
-export function constructArray(elements: AnyPeggyNode[]) {
+export function constructArray(
-  return { type: "Array", elements };
+  elements: AnyPeggyNode[],
+  location: LocationRange
+): NodeArray {
+  return { type: "Array", elements, location };
 }
-export function constructRecord(elements: AnyPeggyNode[]) {
+export function constructRecord(
-  return { type: "Record", elements };
+  elements: NodeKeyValue[],
+  location: LocationRange
+): NodeRecord {
+  return { type: "Record", elements, location };
 }
 
-export function nodeBlock(statements: AnyPeggyNode[]): NodeBlock {
+export function nodeBlock(
-  return { type: "Block", statements };
+  statements: AnyPeggyNode[],
+  location: LocationRange
+): NodeBlock {
+  return { type: "Block", statements, location };
 }
-export function nodeProgram(statements: AnyPeggyNode[]): NodeProgram {
+export function nodeProgram(
-  return { type: "Program", statements };
+  statements: AnyPeggyNode[],
+  location: LocationRange
+): NodeProgram {
+  return { type: "Program", statements, location };
 }
-export function nodeBoolean(value: boolean): NodeBoolean {
+export function nodeBoolean(
-  return { type: "Boolean", value };
+  value: boolean,
+  location: LocationRange
+): NodeBoolean {
+  return { type: "Boolean", value, location };
 }
-export function nodeCall(fn: AnyPeggyNode, args: AnyPeggyNode[]): NodeCall {
+export function nodeCall(
-  return { type: "Call", fn, args };
+  fn: AnyPeggyNode,
+  args: AnyPeggyNode[],
+  location: LocationRange
+): NodeCall {
+  return { type: "Call", fn, args, location };
 }
-export function nodeFloat(value: number): NodeFloat {
+export function nodeFloat(value: number, location: LocationRange): NodeFloat {
-  return { type: "Float", value };
+  return { type: "Float", value, location };
 }
-export function nodeIdentifier(value: string): NodeIdentifier {
+export function nodeIdentifier(
-  return { type: "Identifier", value };
+  value: string,
+  location: LocationRange
+): NodeIdentifier {
+  return { type: "Identifier", value, location };
 }
-export function nodeInteger(value: number): NodeInteger {
+export function nodeInteger(
-  return { type: "Integer", value };
+  value: number,
+  location: LocationRange
+): NodeInteger {
+  return { type: "Integer", value, location };
 }
 export function nodeKeyValue(
   key: AnyPeggyNode,
-  value: AnyPeggyNode
+  value: AnyPeggyNode,
+  location: LocationRange
 ): NodeKeyValue {
   if (key.type === "Identifier") {
     key = {
@@ -173,43 +213,46 @@ export function nodeKeyValue(
       type: "String",
     };
   }
-  return { type: "KeyValue", key, value };
+  return { type: "KeyValue", key, value, location };
 }
 export function nodeLambda(
   args: AnyPeggyNode[],
-  body: AnyPeggyNode
+  body: AnyPeggyNode,
+  location: LocationRange,
+  name?: NodeIdentifier
 ): NodeLambda {
-  return { type: "Lambda", args, body };
+  return { type: "Lambda", args, body, location, name: name?.value };
 }
 export function nodeLetStatement(
   variable: NodeIdentifier,
-  value: AnyPeggyNode
+  value: AnyPeggyNode,
+  location: LocationRange
 ): NodeLetStatement {
-  return { type: "LetStatement", variable, value };
+  const patchedValue =
+    value.type === "Lambda" ? { ...value, name: variable.value } : value;
+  return { type: "LetStatement", variable, value: patchedValue, location };
 }
-export function nodeModuleIdentifier(value: string) {
+export function nodeModuleIdentifier(value: string, location: LocationRange) {
-  return { type: "ModuleIdentifier", value };
+  return { type: "ModuleIdentifier", value, location };
 }
-export function nodeString(value: string): NodeString {
+export function nodeString(value: string, location: LocationRange): NodeString {
-  return { type: "String", value };
+  return { type: "String", value, location };
 }
 export function nodeTernary(
   condition: AnyPeggyNode,
   trueExpression: AnyPeggyNode,
-  falseExpression: AnyPeggyNode
+  falseExpression: AnyPeggyNode,
+  location: LocationRange
 ): NodeTernary {
   return {
     type: "Ternary",
     condition,
     trueExpression,
     falseExpression,
+    location,
   };
 }
 
-export function nodeTypeIdentifier(typeValue: string) {
+export function nodeVoid(location: LocationRange): NodeVoid {
-  return { type: "TypeIdentifier", value: typeValue };
+  return { type: "Void", location };
-}
-
-export function nodeVoid() {
-  return { type: "Void" };
 }

packages/squiggle-lang/src/rescript/Reducer/Reducer_T.res

@@ -15,14 +15,18 @@ type rec value =
   | IEvVoid
 @genType.opaque and arrayValue = array<value>
 @genType.opaque and map = Belt.Map.String.t<value>
-and lambdaBody = (array<value>, environment, reducerFn) => value
+and lambdaBody = (array<value>, context, reducerFn) => value
 @genType.opaque
-and lambdaValue = {
+and lambdaValue =
+  | FnLambda({
       parameters: array<string>,
       body: lambdaBody,
-}
+      location: Reducer_Peggy_Parse.location,
+      name: option<string>,
+    })
+  | FnBuiltin({body: lambdaBody, name: string})
 @genType.opaque and lambdaDeclaration = Declaration.declaration<lambdaValue>
-and expression =
+and expressionContent =
   | EBlock(array<expression>)
   // programs are similar to blocks, but don't create an inner scope. there can be only one program at the top level of the expression.
   | EProgram(array<expression>)
@@ -32,18 +36,34 @@ and expression =
   | ETernary(expression, expression, expression)
   | EAssign(string, expression)
   | ECall(expression, array<expression>)
-  | ELambda(array<string>, expression)
+  | ELambda(array<string>, expression, option<string>)
   | EValue(value)
 
+and expression = {
+  ast: Reducer_Peggy_Parse.ast,
+  content: expressionContent,
+}
+
 and namespace = Belt.Map.String.t<value>
 and bindings = {
   namespace: namespace,
   parent: option<bindings>,
 }
 
+@genType.opaque
+and frame = {
+  name: string,
+  location: option<Reducer_Peggy_Parse.location>, // can be empty for calls from builtin functions
+}
+@genType.opaque and frameStack = list<frame>
+
 and context = {
   bindings: bindings,
   environment: environment,
+  frameStack: frameStack,
+  inFunction: option<lambdaValue>,
 }
 
 and reducerFn = (expression, context) => (value, context)
+
+let topFrameName = "<top>"

packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res

@@ -1,7 +1,3 @@
-// deprecated, use Reducer_T instead
-// (value methods should be moved to Reducer_Value.res)
-
-module ErrorValue = Reducer_ErrorValue
 type environment = GenericDist.env
 module T = Reducer_T
 
@@ -32,10 +28,12 @@ and toStringCall = fName => `:${fName}`
 and toStringDate = date => DateTime.Date.toString(date)
 and toStringDeclaration = d => Declaration.toString(d, r => toString(IEvLambda(r)))
 and toStringDistribution = dist => GenericDist.toString(dist)
-and toStringLambda = (lambdaValue: T.lambdaValue) =>
+and toStringLambda = (lambdaValue: T.lambdaValue) => {
-  `lambda(${Js.Array2.toString(lambdaValue.parameters)}=>internal code)`
+  switch lambdaValue {
-and toStringFunction = (lambdaValue: T.lambdaValue) =>
+  | FnLambda({parameters}) => `lambda(${Js.Array2.toString(parameters)}=>internal code)`
-  `function(${Js.Array2.toString(lambdaValue.parameters)})`
+  | FnBuiltin(_) => "Builtin function"
+  }
+}
 and toStringNumber = aNumber => Js.String.make(aNumber)
 and toStringRecord = aMap => aMap->toStringMap
 and toStringString = aString => `'${aString}'`
@@ -76,25 +74,13 @@ let toStringFunctionCall = ((fn, args)): string => `${fn}(${argsToString(args)})
 let toStringResult = x =>
   switch x {
   | Ok(a) => `Ok(${toString(a)})`
-  | Error(m) => `Error(${ErrorValue.errorToString(m)})`
+  | Error(m) => `Error(${SqError.toString(m)})`
   }
 
-let toStringOptionResult = x =>
+let toStringResultOkless = (codeResult: result<t, SqError.t>): string =>
-  switch x {
-  | Some(a) => toStringResult(a)
-  | None => "None"
-  }
-
-let toStringResultOkless = (codeResult: result<t, ErrorValue.errorValue>): string =>
   switch codeResult {
   | Ok(a) => toString(a)
-  | Error(m) => `Error(${ErrorValue.errorToString(m)})`
+  | Error(m) => `Error(${SqError.toString(m)})`
-  }
-
-let toStringResultRecord = x =>
-  switch x {
-  | Ok(a) => `Ok(${toStringMap(a)})`
-  | Error(m) => `Error(${ErrorValue.errorToString(m)})`
   }
 
 type internalExpressionValueType =
@@ -156,10 +142,10 @@ let functionCallSignatureToString = (functionCallSignature: functionCallSignatur
 
 let arrayToValueArray = (arr: array<t>): array<t> => arr
 
-let resultToValue = (rExpression: result<t, Reducer_ErrorValue.t>): t =>
+let resultToValue = (rExpression: result<t, SqError.Message.t>): t =>
   switch rExpression {
   | Ok(expression) => expression
-  | Error(errorValue) => Reducer_ErrorValue.toException(errorValue)
+  | Error(errorValue) => SqError.Message.throw(errorValue)
   }
 
 let recordToKeyValuePairs = (record: T.map): array<(string, t)> => record->Belt.Map.String.toArray

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res

@@ -1,7 +1,6 @@
 // TODO: Auto clean project based on topology
 
 module Bindings = Reducer_Bindings
-module ErrorValue = Reducer_ErrorValue
 module ProjectItem = ReducerProject_ProjectItem
 module T = ReducerProject_T
 module Topology = ReducerProject_Topology
@@ -121,7 +120,7 @@ let getResultOption = (project: t, sourceId: string): ProjectItem.T.resultType =
 
 let getResult = (project: t, sourceId: string): ProjectItem.T.resultArgumentType =>
   switch getResultOption(project, sourceId) {
-  | None => RENeedToRun->Error
+  | None => RENeedToRun->SqError.fromMessage->Error
   | Some(result) => result
   }
 
@@ -175,7 +174,7 @@ let linkDependencies = (project: t, sourceId: string): Reducer_T.namespace => {
             "__result__",
             switch project->getResult(id) {
             | Ok(result) => result
-            | Error(error) => error->Reducer_ErrorValue.ErrorException->raise
+            | Error(error) => error->SqError.throw
             },
           ),
         ])

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ParseIncludes.res

@@ -1,10 +1,7 @@
 @module("./ReducerProject_IncludeParser.js")
 external parse__: string => array<array<string>> = "parse"
 
-let parseIncludes = (expr: string): result<
+let parseIncludes = (expr: string): result<array<(string, string)>, SqError.t> =>
-  array<(string, string)>,
-  Reducer_ErrorValue.errorValue,
-> =>
   try {
     let answer = parse__(expr)
     // let logEntry = answer->Js.Array2.joinWith(",")
@@ -12,8 +9,9 @@ let parseIncludes = (expr: string): result<
     Belt.Array.map(answer, item => (item[0], item[1]))->Ok
   } catch {
   | Js.Exn.Error(obj) =>
-    RESyntaxError(
+    RESyntaxError(Belt.Option.getExn(Js.Exn.message(obj)))
-      Belt.Option.getExn(Js.Exn.message(obj)),
+    ->SqError.fromMessageWithFrameStack(
-      Reducer_Peggy_Parse.syntaxErrorToLocation(obj)->Some,
+      Reducer_FrameStack.makeSingleFrameStack(Reducer_Peggy_Parse.syntaxErrorToLocation(obj)),
-    )->Error
+    )
+    ->Error
   }

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res

@@ -4,8 +4,9 @@ module T = ReducerProject_ProjectItem_T
 type projectItem = T.projectItem
 type t = T.t
 
-let emptyItem: projectItem = {
+let emptyItem = (sourceId: string): projectItem => {
   source: "",
+  sourceId: sourceId,
   rawParse: None,
   expression: None,
   continuation: Reducer_Namespace.make(),
@@ -18,6 +19,7 @@ let emptyItem: projectItem = {
 // source -> rawParse -> includes -> expression -> continuation -> result
 
 let getSource = (r: t): T.sourceType => r.source
+let getSourceId = (r: t): T.sourceType => r.sourceId
 let getRawParse = (r: t): T.rawParseType => r.rawParse
 let getExpression = (r: t): T.expressionType => r.expression
 let getContinuation = (r: t): T.continuationArgumentType => r.continuation
@@ -29,7 +31,7 @@ let getDirectIncludes = (r: t): array<string> => r.directIncludes
 let getIncludesAsVariables = (r: t): T.importAsVariablesType => r.includeAsVariables
 
 let touchSource = (this: t): t => {
-  let r = emptyItem
+  let r = emptyItem(this->getSourceId)
   {
     ...r,
     source: getSource(this),
@@ -41,8 +43,9 @@ let touchSource = (this: t): t => {
 }
 
 let touchRawParse = (this: t): t => {
+  let r = emptyItem(this->getSourceId)
   {
-    ...emptyItem,
+    ...r,
     source: getSource(this),
     continues: getContinues(this),
     includes: getIncludes(this),
@@ -148,7 +151,8 @@ let parseIncludes = (this: t): t => {
     }
   }
 }
-let doRawParse = (this: t): T.rawParseArgumentType => this->getSource->Reducer_Peggy_Parse.parse
+let doRawParse = (this: t): T.rawParseArgumentType =>
+  this->getSource->Reducer_Peggy_Parse.parse(this.sourceId)->E.R2.errMap(SqError.fromParseError)
 
 let rawParse = (this: t): t =>
   this->getRawParse->E.O2.defaultFn(() => doRawParse(this))->setRawParse(this, _)
@@ -167,7 +171,7 @@ let buildExpression = (this: t): t => {
   }
 }
 
-let failRun = (this: t, e: Reducer_ErrorValue.errorValue): t =>
+let failRun = (this: t, e: SqError.t): t =>
   this->setResult(e->Error)->setContinuation(Reducer_Namespace.make())
 
 let doRun = (this: t, context: Reducer_T.context): t =>
@@ -181,12 +185,11 @@ let doRun = (this: t, context: Reducer_T.context): t =>
         ->setResult(result->Ok)
         ->setContinuation(contextAfterEvaluation.bindings->Reducer_Bindings.locals)
       } catch {
-      | Reducer_ErrorValue.ErrorException(e) => this->failRun(e)
+      | e => this->failRun(e->SqError.fromException)
-      | _ => this->failRun(RETodo("unhandled rescript exception"))
       }
     | Error(e) => this->failRun(e)
     }
-  | None => this->failRun(RETodo("attempt to run without expression"))
+  | None => this->failRun(RETodo("attempt to run without expression")->SqError.fromMessage)
   }
 
 let run = (this: t, context: Reducer_T.context): t => {

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res

@@ -1,26 +1,24 @@
 module Parse = Reducer_Peggy_Parse
 module ExpressionT = Reducer_Expression_T
-open Reducer_ErrorValue
 
 type sourceArgumentType = string
 type sourceType = string
-type rawParseArgumentType = result<Parse.node, errorValue>
+type rawParseArgumentType = result<Parse.node, SqError.t>
 type rawParseType = option<rawParseArgumentType>
-type expressionArgumentType = result<ExpressionT.t, errorValue>
+type expressionArgumentType = result<ExpressionT.t, SqError.t>
 type expressionType = option<expressionArgumentType>
 type continuationArgumentType = Reducer_T.namespace
-type continuationType = option<continuationArgumentType>
+type resultArgumentType = result<Reducer_T.value, SqError.t>
-type continuationResultType = option<result<continuationArgumentType, errorValue>>
-type resultArgumentType = result<Reducer_T.value, errorValue>
 type resultType = option<resultArgumentType>
 type continuesArgumentType = array<string>
 type continuesType = array<string>
 type includesArgumentType = string
-type includesType = result<array<string>, errorValue>
+type includesType = result<array<string>, SqError.t>
 type importAsVariablesType = array<(string, string)>
 
 type projectItem = {
   source: sourceType,
+  sourceId: string,
   rawParse: rawParseType,
   expression: expressionType,
   continuation: continuationArgumentType,

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_T.res

@@ -13,4 +13,4 @@ type t = project
 let getSourceIds = (project: t): array<string> => Belt.MutableMap.String.keysToArray(project.items)
 
 let getItem = (project: t, sourceId: string) =>
-  Belt.MutableMap.String.getWithDefault(project.items, sourceId, ProjectItem.emptyItem)
+  Belt.MutableMap.String.getWithDefault(project.items, sourceId, ProjectItem.emptyItem(sourceId))

packages/squiggle-lang/src/rescript/SqError.res

@@ -0,0 +1,159 @@
+type location = Reducer_Peggy_Parse.location
+
+// Messages don't contain any stack trace information.
+// FunctionRegistry functions are allowed to throw MessageExceptions, though,
+// because they will be caught and rewrapped by Reducer_Lambda code.
+module Message = {
+  @genType.opaque
+  type t =
+    | REArityError(option<string>, int, int)
+    | REArrayIndexNotFound(string, int)
+    | REAssignmentExpected
+    | REDistributionError(DistributionTypes.error)
+    | REExpectedType(string, string)
+    | REExpressionExpected
+    | REFunctionExpected(string)
+    | REFunctionNotFound(string)
+    | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
+    | REMacroNotFound(string)
+    | RENotAFunction(string)
+    | REOperationError(Operation.operationError)
+    | RERecordPropertyNotFound(string, string)
+    | RESymbolNotFound(string)
+    | RESyntaxError(string)
+    | RETodo(string) // To do
+    | REUnitNotFound(string)
+    | RENeedToRun
+    | REOther(string)
+
+  exception MessageException(t)
+
+  let toString = (err: t) =>
+    switch err {
+    | REArityError(_oFnName, arity, usedArity) =>
+      `${Js.String.make(arity)} arguments expected. Instead ${Js.String.make(
+          usedArity,
+        )} argument(s) were passed.`
+    | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
+    | REAssignmentExpected => "Assignment expected"
+    | REExpressionExpected => "Expression expected"
+    | REFunctionExpected(msg) => `Function expected: ${msg}`
+    | REFunctionNotFound(msg) => `Function not found: ${msg}`
+    | REDistributionError(err) =>
+      `Distribution Math Error: ${DistributionTypes.Error.toString(err)}`
+    | REOperationError(err) => `Math Error: ${Operation.Error.toString(err)}`
+    | REJavaScriptExn(omsg, oname) => {
+        let answer = "JS Exception:"
+        let answer = switch oname {
+        | Some(name) => `${answer} ${name}`
+        | _ => answer
+        }
+        let answer = switch omsg {
+        | Some(msg) => `${answer}: ${msg}`
+        | _ => answer
+        }
+        answer
+      }
+    | REMacroNotFound(macro) => `Macro not found: ${macro}`
+    | RENotAFunction(valueString) => `${valueString} is not a function`
+    | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
+    | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
+    | RESyntaxError(desc) => `Syntax Error: ${desc}`
+    | RETodo(msg) => `TODO: ${msg}`
+    | REExpectedType(typeName, valueString) => `Expected type: ${typeName} but got: ${valueString}`
+    | REUnitNotFound(unitName) => `Unit not found: ${unitName}`
+    | RENeedToRun => "Need to run"
+    | REOther(msg) => `Error: ${msg}`
+    }
+
+  let fromException = exn =>
+    switch exn {
+    | MessageException(e) => e
+    | Js.Exn.Error(e) =>
+      switch Js.Exn.message(e) {
+      | Some(message) => REOther(message)
+      | None =>
+        switch Js.Exn.name(e) {
+        | Some(name) => REOther(name)
+        | None => REOther("Unknown error")
+        }
+      }
+    | _e => REOther("Unknown error")
+    }
+
+  let throw = (errorValue: t) => errorValue->MessageException->raise
+}
+
+@genType.opaque
+type t = {
+  message: Message.t,
+  frameStack: Reducer_FrameStack.t,
+}
+
+exception SqException(t)
+
+let fromMessageWithFrameStack = (message: Message.t, frameStack: Reducer_FrameStack.t): t => {
+  message: message,
+  frameStack: frameStack,
+}
+
+// this shouldn't be used much, since frame stack will be empty
+// but it's useful for global errors, e.g. in ReducerProject or somethere in the frontend
+@genType
+let fromMessage = (message: Message.t) =>
+  fromMessageWithFrameStack(message, Reducer_FrameStack.make())
+
+let fromParseError = (SyntaxError(message, location): Reducer_Peggy_Parse.parseError) =>
+  RESyntaxError(message)->fromMessageWithFrameStack(
+    Reducer_FrameStack.makeSingleFrameStack(location),
+  )
+
+@genType
+let getTopFrame = (t: t): option<Reducer_T.frame> => t.frameStack->Reducer_FrameStack.getTopFrame
+
+@genType
+let getFrameStack = (t: t): Reducer_FrameStack.t => t.frameStack
+
+@genType
+let toString = (t: t): string => t.message->Message.toString
+
+@genType
+let createOtherError = (v: string): t => Message.REOther(v)->fromMessage
+
+@genType
+let getFrameArray = (t: t): array<Reducer_T.frame> => t.frameStack->Reducer_FrameStack.toFrameArray
+
+@genType
+let toStringWithStackTrace = (t: t) =>
+  t->toString ++ if t.frameStack->Reducer_FrameStack.isEmpty {
+      "\nStack trace:\n" ++ t.frameStack->Reducer_FrameStack.toString
+    } else {
+      ""
+    }
+let throw = (t: t) => t->SqException->raise
+
+let throwMessageWithFrameStack = (message: Message.t, frameStack: Reducer_FrameStack.t) =>
+  message->fromMessageWithFrameStack(frameStack)->throw
+
+// this shouldn't be used for most runtime errors - the resulting error would have an empty framestack
+let fromException = exn =>
+  switch exn {
+  | SqException(e) => e
+  | Message.MessageException(e) => e->fromMessage
+  | Js.Exn.Error(obj) => REJavaScriptExn(obj->Js.Exn.message, obj->Js.Exn.name)->fromMessage
+  | _ => REOther("Unknown exception")->fromMessage
+  }
+
+// converts raw exceptions into exceptions with framestack attached
+// already converted exceptions won't be affected
+let rethrowWithFrameStack = (fn: unit => 'a, frameStack: Reducer_FrameStack.t) => {
+  try {
+    fn()
+  } catch {
+  | SqException(e) => e->throw // exception already has a framestack
+  | Message.MessageException(e) => e->throwMessageWithFrameStack(frameStack) // probably comes from FunctionRegistry, adding framestack
+  | Js.Exn.Error(obj) =>
+    REJavaScriptExn(obj->Js.Exn.message, obj->Js.Exn.name)->throwMessageWithFrameStack(frameStack)
+  | _ => REOther("Unknown exception")->throwMessageWithFrameStack(frameStack)
+  }
+}

packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_StdLib.res

@@ -1,5 +1,3 @@
-exception ErrorException = Reducer_ErrorValue.ErrorException
-
 let stdLib: Reducer_T.namespace = {
   // constants
   let res =
@@ -10,23 +8,23 @@ let stdLib: Reducer_T.namespace = {
   // array and record lookups
   let res = res->Reducer_Namespace.set(
     "$_atIndex_$",
-    Reducer_Expression_Lambda.makeFFILambda((inputs, _, _) => {
+    Reducer_Lambda.makeFFILambda("$_atIndex_$", (inputs, _, _) => {
       switch inputs {
       | [IEvArray(aValueArray), IEvNumber(fIndex)] => {
           let index = Belt.Int.fromFloat(fIndex) // TODO - fail on non-integer indices?
 
           switch Belt.Array.get(aValueArray, index) {
           | Some(value) => value
-          | None => REArrayIndexNotFound("Array index not found", index)->ErrorException->raise
+          | None => REArrayIndexNotFound("Array index not found", index)->SqError.Message.throw
           }
         }
       | [IEvRecord(dict), IEvString(sIndex)] =>
         switch Belt.Map.String.get(dict, sIndex) {
         | Some(value) => value
         | None =>
-          RERecordPropertyNotFound("Record property not found", sIndex)->ErrorException->raise
+          RERecordPropertyNotFound("Record property not found", sIndex)->SqError.Message.throw
         }
-      | _ => REOther("Trying to access key on wrong value")->ErrorException->raise
+      | _ => REOther("Trying to access key on wrong value")->SqError.Message.throw
       }
     })->Reducer_T.IEvLambda,
   )
@@ -46,10 +44,10 @@ let stdLib: Reducer_T.namespace = {
     ->Belt.Array.reduce(res, (cur, name) => {
       cur->Reducer_Namespace.set(
         name,
-        Reducer_Expression_Lambda.makeFFILambda((arguments, environment, reducer) => {
+        Reducer_Lambda.makeFFILambda(name, (arguments, context, reducer) => {
-          switch FunctionRegistry_Library.call(name, arguments, environment, reducer) {
+          switch FunctionRegistry_Library.call(name, arguments, context, reducer) {
           | Ok(value) => value
-          | Error(error) => error->Reducer_ErrorValue.ErrorException->raise
+          | Error(error) => error->SqError.Message.throw
           }
         })->Reducer_T.IEvLambda,
       )