diff --git a/packages/components/src/components/CodeEditor.tsx b/packages/components/src/components/CodeEditor.tsx
index 15802131..ec2fdee7 100644
--- a/packages/components/src/components/CodeEditor.tsx
+++ b/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",
+      }))}
     />
   );
 };
diff --git a/packages/components/src/components/SquiggleChart.tsx b/packages/components/src/components/SquiggleChart.tsx
index 4dd57a1f..2e126d4c 100644
--- a/packages/components/src/components/SquiggleChart.tsx
+++ b/packages/components/src/components/SquiggleChart.tsx
@@ -9,6 +9,7 @@ import {
 import { useSquiggle } from "../lib/hooks";
 import { SquiggleViewer } from "./SquiggleViewer";
 import { JsImports } from "../lib/jsImports";
+import { getValueToRender } from "../lib/utility";
 
 export interface SquiggleChartProps {
   /** The input string for squiggle */
@@ -58,16 +59,9 @@ export interface SquiggleChartProps {
 const defaultOnChange = () => {};
 const defaultImports: JsImports = {};
 
-export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
-  ({
-    code = "",
-    executionId = 0,
-    environment,
-    onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
-    height = 200,
-    jsImports = defaultImports,
+export const splitSquiggleChartSettings = (props: SquiggleChartProps) => {
+  const {
     showSummary = false,
-    width,
     logX = false,
     expY = false,
     diagramStart = 0,
@@ -80,9 +74,47 @@ export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
     title,
     xAxisType = "number",
     distributionChartActions,
-    enableLocalSettings = false,
-  }) => {
-    const { result, bindings } = useSquiggle({
+  } = props;
+
+  const distributionPlotSettings = {
+    showSummary,
+    logX,
+    expY,
+    format: tickFormat,
+    minX,
+    maxX,
+    color,
+    title,
+    xAxisType,
+    actions: distributionChartActions,
+  };
+
+  const chartSettings = {
+    start: diagramStart,
+    stop: diagramStop,
+    count: diagramCount,
+  };
+
+  return { distributionPlotSettings, chartSettings };
+};
+
+export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
+  (props) => {
+    const { distributionPlotSettings, chartSettings } =
+      splitSquiggleChartSettings(props);
+
+    const {
+      code = "",
+      environment,
+      jsImports = defaultImports,
+      onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
+      executionId = 0,
+      width,
+      height = 200,
+      enableLocalSettings = false,
+    } = props;
+
+    const resultAndBindings = useSquiggle({
       code,
       environment,
       jsImports,
@@ -90,32 +122,11 @@ export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
       executionId,
     });
 
-    const distributionPlotSettings = {
-      showSummary,
-      logX,
-      expY,
-      format: tickFormat,
-      minX,
-      maxX,
-      color,
-      title,
-      xAxisType,
-      actions: distributionChartActions,
-    };
-
-    const chartSettings = {
-      start: diagramStart,
-      stop: diagramStop,
-      count: diagramCount,
-    };
-
-    const resultToRender = resultMap(result, (value) =>
-      value.tag === SqValueTag.Void ? bindings.asValue() : value
-    );
+    const valueToRender = getValueToRender(resultAndBindings);
 
     return (
       <SquiggleViewer
-        result={resultToRender}
+        result={valueToRender}
         width={width}
         height={height}
         distributionPlotSettings={distributionPlotSettings}
diff --git a/packages/components/src/components/SquiggleEditor.tsx b/packages/components/src/components/SquiggleEditor.tsx
index 9a11ac44..731b5d0c 100644
--- a/packages/components/src/components/SquiggleEditor.tsx
+++ b/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 { useMaybeControlledValue } from "../lib/hooks";
+import {
+  splitSquiggleChartSettings,
+  SquiggleChartProps,
+} from "./SquiggleChart";
+import { useMaybeControlledValue, useSquiggle } from "../lib/hooks";
+import { JsImports } from "../lib/jsImports";
+import { defaultEnvironment, SqLocation } 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 +43,46 @@ 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 resultAndBindings = useSquiggle({
+    code,
+    environment,
+    jsImports,
+    onChange,
+    executionId,
+  });
+
+  const valueToRender = getValueToRender(resultAndBindings);
+  const errorLocations = getErrorLocations(resultAndBindings.result);
+
   return (
     <SquiggleContainer>
-      <WrappedCodeEditor code={code} setCode={setCode} />
-      <SquiggleChart {...chartProps} />
+      <WrappedCodeEditor
+        code={code}
+        setCode={setCode}
+        errorLocations={errorLocations}
+      />
+      <SquiggleViewer
+        result={valueToRender}
+        width={width}
+        height={height}
+        distributionPlotSettings={distributionPlotSettings}
+        chartSettings={chartSettings}
+        environment={environment ?? defaultEnvironment}
+        enableLocalSettings={enableLocalSettings}
+      />
     </SquiggleContainer>
   );
 };
diff --git a/packages/components/src/components/SquiggleErrorAlert.tsx b/packages/components/src/components/SquiggleErrorAlert.tsx
index e9dd4245..fb4721eb 100644
--- a/packages/components/src/components/SquiggleErrorAlert.tsx
+++ b/packages/components/src/components/SquiggleErrorAlert.tsx
@@ -17,21 +17,24 @@ const StackTraceLocation: React.FC<{ location: SqLocation }> = ({
 };
 
 const StackTrace: React.FC<Props> = ({ error }) => {
-  return (
+  const locations = error.toLocationArray();
+  return locations.length ? (
     <div>
-      {error.toLocationArray().map((location, i) => (
-        <StackTraceLocation location={location} key={i} />
-      ))}
+      <div>Traceback:</div>
+      <div className="ml-4">
+        {locations.map((location, i) => (
+          <StackTraceLocation location={location} key={i} />
+        ))}
+      </div>
     </div>
-  );
+  ) : null;
 };
 
 export const SquiggleErrorAlert: React.FC<Props> = ({ error }) => {
   return (
     <ErrorAlert heading="Error">
-      <div>{error.toString()}</div>
-      <div className="mt-4">Traceback:</div>
-      <div className="ml-4">
+      <div className="space-y-4">
+        <div>{error.toString()}</div>
         <StackTrace error={error} />
       </div>
     </ErrorAlert>
diff --git a/packages/components/src/components/SquigglePlayground.tsx b/packages/components/src/components/SquigglePlayground.tsx
index 8039bbe0..de467918 100644
--- a/packages/components/src/components/SquigglePlayground.tsx
+++ b/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,
@@ -26,7 +30,7 @@ import clsx from "clsx";
 
 import { environment } 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 +305,51 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
     executionId,
   } = useRunnerState(code);
 
+  const resultAndBindings = useSquiggle({
+    code,
+    environment,
+    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
-          code={renderedCode}
-          executionId={executionId}
-          environment={env}
-          {...vars}
-          jsImports={imports}
+        <SquiggleViewer
+          result={valueToRender}
+          environment={environment}
+          height={vars.chartHeight || 150}
+          distributionPlotSettings={{
+            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}
diff --git a/packages/components/src/lib/hooks/useSquiggle.ts b/packages/components/src/lib/hooks/useSquiggle.ts
index 5916ac54..b2812d6f 100644
--- a/packages/components/src/lib/hooks/useSquiggle.ts
+++ b/packages/components/src/lib/hooks/useSquiggle.ts
@@ -1,4 +1,11 @@
-import { environment, SqProject, SqValue } from "@quri/squiggle-lang";
+import {
+  environment,
+  result,
+  SqError,
+  SqProject,
+  SqRecord,
+  SqValue,
+} from "@quri/squiggle-lang";
 import { useEffect, useMemo } from "react";
 import { JsImports, jsImportsToSquiggleCode } from "../jsImports";
 
@@ -10,7 +17,12 @@ type SquiggleArgs = {
   onChange?: (expr: SqValue | undefined) => void;
 };
 
-export const useSquiggle = (args: SquiggleArgs) => {
+export type ResultAndBindings = {
+  result: result<SqValue, SqError>;
+  bindings: SqRecord;
+};
+
+export const useSquiggle = (args: SquiggleArgs): ResultAndBindings => {
   const result = useMemo(
     () => {
       const project = SqProject.create();
diff --git a/packages/components/src/lib/utility.ts b/packages/components/src/lib/utility.ts
index d4d3661b..c3ce08a4 100644
--- a/packages/components/src/lib/utility.ts
+++ b/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.toLocation();
+    return location ? [location] : [];
+  } else {
+    return [];
+  }
+}
diff --git a/packages/components/src/styles/main.css b/packages/components/src/styles/main.css
index 987c3714..257c5712 100644
--- a/packages/components/src/styles/main.css
+++ b/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;
+}
diff --git a/packages/squiggle-lang/src/js/SqError.ts b/packages/squiggle-lang/src/js/SqError.ts
index 5025e671..5e599e51 100644
--- a/packages/squiggle-lang/src/js/SqError.ts
+++ b/packages/squiggle-lang/src/js/SqError.ts
@@ -22,4 +22,8 @@ export class SqError {
 
     return stackTrace ? RSError.StackTrace.toLocationArray(stackTrace) : [];
   }
+
+  toLocation() {
+    return RSError.getLocation(this._value);
+  }
 }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
index d33d7ba3..10e026a3 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
@@ -98,7 +98,7 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.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
       })