Merge remote-tracking branch 'origin/develop' into scoring-cleanup-three

2022-07-11 14:20:00 -04:00 · 2022-07-11 14:20:00 -04:00 · d682f28faf
commit d682f28faf
parent 7889332052 c6b3e05365
56 changed files with 2659 additions and 1754 deletions
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@ -9,8 +9,8 @@
 # This also holds true for GitHub teams.

 # Rescript 
-*.res @OAGr @quinn-dougherty
-*.resi @OAGr @quinn-dougherty
+*.res @OAGr
+*.resi @OAGr

 # Typescript 
 *.tsx @Hazelfire @OAGr
--- a/packages/components/README.md
+++ b/packages/components/README.md
@ -20,7 +20,7 @@ Add to `App.js`:
 ```jsx
 import { SquiggleEditor } from "@quri/squiggle-components";
 <SquiggleEditor
-  initialSquiggleString="x = beta($alpha, 10); x + $shift"
+  defaultCode="x = beta($alpha, 10); x + $shift"
  jsImports={{ alpha: 3, shift: 20 }}
 />;
 ```
@ -50,7 +50,7 @@ export function DynamicSquiggleChart({ squiggleString }) {
  } else {
    return (
        <SquiggleChart
-          squiggleString={squiggleString}
+          defaultCode={squiggleString}
          width={445}
          height={200}
          showSummary={true}
--- a/packages/components/package.json
+++ b/packages/components/package.json
@ -3,26 +3,27 @@
  "version": "0.2.20",
  "license": "MIT",
  "dependencies": {
-    "@headlessui/react": "^1.6.5",
+    "@headlessui/react": "^1.6.6",
    "@heroicons/react": "^1.0.6",
-    "@hookform/resolvers": "^2.9.3",
+    "@hookform/resolvers": "^2.9.5",
    "@quri/squiggle-lang": "^0.2.8",
    "@react-hook/size": "^2.1.2",
-    "clsx": "^1.1.1",
+    "clsx": "^1.2.1",
+    "framer-motion": "^6.4.3",
    "lodash": "^4.17.21",
    "react": "^18.1.0",
    "react-ace": "^10.1.0",
-    "react-hook-form": "^7.33.0",
+    "react-hook-form": "^7.33.1",
    "react-use": "^17.4.0",
-    "react-vega": "^7.5.1",
+    "react-vega": "^7.6.0",
    "vega": "^5.22.1",
    "vega-embed": "^6.21.0",
-    "vega-lite": "^5.2.0",
+    "vega-lite": "^5.3.0",
    "vscode-uri": "^3.0.3",
    "yup": "^0.32.11"
  },
  "devDependencies": {
-    "@babel/plugin-proposal-private-property-in-object": "^7.17.12",
+    "@babel/plugin-proposal-private-property-in-object": "^7.18.6",
    "@storybook/addon-actions": "^6.5.9",
    "@storybook/addon-essentials": "^6.5.9",
    "@storybook/addon-links": "^6.5.9",
@ -36,28 +37,26 @@
    "@testing-library/user-event": "^14.2.1",
    "@types/jest": "^27.5.0",
    "@types/lodash": "^4.14.182",
-    "@types/node": "^18.0.0",
+    "@types/node": "^18.0.3",
    "@types/react": "^18.0.9",
-    "@types/react-dom": "^18.0.5",
    "@types/styled-components": "^5.1.24",
    "@types/webpack": "^5.28.0",
    "cross-env": "^7.0.3",
    "mini-css-extract-plugin": "^2.6.1",
-    "postcss-cli": "^9.1.0",
+    "postcss-cli": "^10.0.0",
    "postcss-import": "^14.1.0",
-    "postcss-loader": "^7.0.0",
+    "postcss-loader": "^7.0.1",
    "react": "^18.1.0",
-    "react-dom": "^18.2.0",
    "react-scripts": "^5.0.1",
    "style-loader": "^3.3.1",
-    "tailwindcss": "^3.1.3",
+    "tailwindcss": "^3.1.5",
    "ts-loader": "^9.3.0",
    "tsconfig-paths-webpack-plugin": "^3.5.2",
    "typescript": "^4.7.4",
    "web-vitals": "^2.1.4",
    "webpack": "^5.73.0",
    "webpack-cli": "^4.10.0",
-    "webpack-dev-server": "^4.9.2"
+    "webpack-dev-server": "^4.9.3"
  },
  "peerDependencies": {
    "react": "^16.8.0 || ^17 || ^18",
--- a/packages/components/src/components/CodeEditor.tsx
+++ b/packages/components/src/components/CodeEditor.tsx
@ -1,5 +1,5 @@
 import _ from "lodash";
-import React, { FC, useMemo } from "react";
+import React, { FC, useMemo, useRef } from "react";
 import AceEditor from "react-ace";

 import "ace-builds/src-noconflict/mode-golang";
@ -8,6 +8,7 @@ import "ace-builds/src-noconflict/theme-github";
 interface CodeEditorProps {
  value: string;
  onChange: (value: string) => void;
+  onSubmit?: () => void;
  oneLine?: boolean;
  width?: number;
  height: number;
@ -17,6 +18,7 @@ interface CodeEditorProps {
 export const CodeEditor: FC<CodeEditorProps> = ({
  value,
  onChange,
+  onSubmit,
  oneLine = false,
  showGutter = false,
  height,
@ -24,6 +26,10 @@ export const CodeEditor: FC<CodeEditorProps> = ({
  const lineCount = value.split("\n").length;
  const id = useMemo(() => _.uniqueId(), []);

+  // this is necessary because AceEditor binds commands on mount, see https://github.com/securingsincity/react-ace/issues/684
+  const onSubmitRef = useRef<typeof onSubmit | null>(null);
+  onSubmitRef.current = onSubmit;
+
  return (
    <AceEditor
      value={value}
@ -46,6 +52,13 @@ export const CodeEditor: FC<CodeEditorProps> = ({
        enableBasicAutocompletion: false,
        enableLiveAutocompletion: false,
      }}
+      commands={[
+        {
+          name: "submit",
+          bindKey: { mac: "Cmd-Enter", win: "Ctrl-Enter" },
+          exec: () => onSubmitRef.current?.(),
+        },
+      ]}
    />
  );
 };
--- a/packages/components/src/components/SquiggleChart.tsx
+++ b/packages/components/src/components/SquiggleChart.tsx
@ -8,20 +8,23 @@ import {
  defaultBindings,
  defaultEnvironment,
 } from "@quri/squiggle-lang";
-import { FunctionChartSettings } from "./FunctionChart";
 import { useSquiggle } from "../lib/hooks";
 import { SquiggleErrorAlert } from "./SquiggleErrorAlert";
 import { SquiggleItem } from "./SquiggleItem";

 export interface SquiggleChartProps {
  /** The input string for squiggle */
-  squiggleString?: string;
+  code?: string;
  /** If the output requires monte carlo sampling, the amount of samples */
  sampleCount?: number;
  /** The amount of points returned to draw the distribution */
  environment?: environment;
-  /** If the result is a function, where the function starts, ends and the amount of stops */
-  chartSettings?: FunctionChartSettings;
+  /** If the result is a function, where the function domain starts */
+  diagramStart?: number;
+  /** If the result is a function, where the function domain ends */
+  diagramStop?: number;
+  /** If the result is a function, the amount of stops sampled */
+  diagramCount?: number;
  /** When the squiggle code gets reevaluated */
  onChange?(expr: squiggleExpression | undefined): void;
  /** CSS width of the element */
@ -44,51 +47,60 @@ export interface SquiggleChartProps {
 }

 const defaultOnChange = () => {};
-const defaultChartSettings = { start: 0, stop: 10, count: 20 };

-export const SquiggleChart: React.FC<SquiggleChartProps> = ({
-  squiggleString = "",
-  environment,
-  onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
-  height = 200,
-  bindings = defaultBindings,
-  jsImports = defaultImports,
-  showSummary = false,
-  width,
-  showTypes = false,
-  showControls = false,
-  logX = false,
-  expY = false,
-  chartSettings = defaultChartSettings,
-}) => {
-  const { result } = useSquiggle({
-    code: squiggleString,
-    bindings,
+export const SquiggleChart: React.FC<SquiggleChartProps> = React.memo(
+  ({
+    code = "",
    environment,
-    jsImports,
-    onChange,
-  });
+    onChange = defaultOnChange, // defaultOnChange must be constant, don't move its definition here
+    height = 200,
+    bindings = defaultBindings,
+    jsImports = defaultImports,
+    showSummary = false,
+    width,
+    showTypes = false,
+    showControls = false,
+    logX = false,
+    expY = false,
+    diagramStart = 0,
+    diagramStop = 10,
+    diagramCount = 100,
+  }) => {
+    const result = useSquiggle({
+      code,
+      bindings,
+      environment,
+      jsImports,
+      onChange,
+    });

-  if (result.tag !== "Ok") {
-    return <SquiggleErrorAlert error={result.value} />;
+    if (result.tag !== "Ok") {
+      return <SquiggleErrorAlert error={result.value} />;
+    }
+
+    let distributionPlotSettings = {
+      showControls,
+      showSummary,
+      logX,
+      expY,
+    };
+
+    let chartSettings = {
+      start: diagramStart,
+      stop: diagramStop,
+      count: diagramCount,
+    };
+
+    return (
+      <SquiggleItem
+        expression={result.value}
+        width={width}
+        height={height}
+        distributionPlotSettings={distributionPlotSettings}
+        showTypes={showTypes}
+        chartSettings={chartSettings}
+        environment={environment ?? defaultEnvironment}
+      />
+    );
  }
-
-  let distributionPlotSettings = {
-    showControls,
-    showSummary,
-    logX,
-    expY,
-  };
-
-  return (
-    <SquiggleItem
-      expression={result.value}
-      width={width}
-      height={height}
-      distributionPlotSettings={distributionPlotSettings}
-      showTypes={showTypes}
-      chartSettings={chartSettings}
-      environment={environment ?? defaultEnvironment}
-    />
-  );
-};
+);
--- a/packages/components/src/components/SquiggleEditor.tsx
+++ b/packages/components/src/components/SquiggleEditor.tsx
@ -1,18 +1,11 @@
-import React, { useState } from "react";
-import * as ReactDOM from "react-dom";
+import React from "react";
 import { CodeEditor } from "./CodeEditor";
-import {
-  squiggleExpression,
-  environment,
-  bindings,
-  jsImports,
-  defaultEnvironment,
-} from "@quri/squiggle-lang";
+import { environment, bindings, jsImports } from "@quri/squiggle-lang";
 import { defaultImports, defaultBindings } from "@quri/squiggle-lang";
 import { SquiggleContainer } from "./SquiggleContainer";
-import { useSquiggle, useSquigglePartial } from "../lib/hooks";
+import { SquiggleChart, SquiggleChartProps } from "./SquiggleChart";
+import { useSquigglePartial, useMaybeControlledValue } from "../lib/hooks";
 import { SquiggleErrorAlert } from "./SquiggleErrorAlert";
-import { SquiggleItem } from "./SquiggleItem";

 const WrappedCodeEditor: React.FC<{
  code: string;
@ -29,113 +22,36 @@ const WrappedCodeEditor: React.FC<{
  </div>
 );

-export interface SquiggleEditorProps {
-  /** The input string for squiggle */
-  initialSquiggleString?: string;
-  /** The width of the element */
-  width?: number;
-  /** If the result is a function, where the function starts */
-  diagramStart?: number;
-  /** If the result is a function, where the function ends */
-  diagramStop?: number;
-  /** If the result is a function, how many points along the function it samples */
-  diagramCount?: number;
-  /** When the environment changes. Used again for notebook magic */
-  onChange?(expr: squiggleExpression | undefined): void;
-  /** Previous variable declarations */
-  bindings?: bindings;
-  /** If the output requires monte carlo sampling, the amount of samples */
-  environment?: environment;
-  /** JS Imports */
-  jsImports?: jsImports;
-  /** Whether to show detail about types of the returns, default false */
-  showTypes?: boolean;
-  /** Whether to give users access to graph controls */
-  showControls?: boolean;
-  /** Whether to show a summary table */
-  showSummary?: boolean;
-  /** Whether to log the x coordinate on distribution charts */
-  logX?: boolean;
-  /** Whether to exp the y coordinate on distribution charts */
-  expY?: boolean;
-}
+export type SquiggleEditorProps = SquiggleChartProps & {
+  defaultCode?: string;
+  onCodeChange?: (code: string) => void;
+};

-export const SquiggleEditor: React.FC<SquiggleEditorProps> = ({
-  initialSquiggleString = "",
-  width,
-  diagramStart = 0,
-  diagramStop = 10,
-  diagramCount = 20,
-  onChange,
-  bindings = defaultBindings,
-  environment,
-  jsImports = defaultImports,
-  showTypes = false,
-  showControls = false,
-  showSummary = false,
-  logX = false,
-  expY = false,
-}: SquiggleEditorProps) => {
-  const [code, setCode] = useState(initialSquiggleString);
-  React.useEffect(
-    () => setCode(initialSquiggleString),
-    [initialSquiggleString]
-  );
-
-  const { result, observableRef } = useSquiggle({
-    code,
-    bindings,
-    environment,
-    jsImports,
-    onChange,
+export const SquiggleEditor: React.FC<SquiggleEditorProps> = (props) => {
+  const [code, setCode] = useMaybeControlledValue({
+    value: props.code,
+    defaultValue: props.defaultCode ?? "",
+    onChange: props.onCodeChange,
  });

-  const chartSettings = {
-    start: diagramStart,
-    stop: diagramStop,
-    count: diagramCount,
-  };
-
-  const distributionPlotSettings = {
-    showControls,
-    showSummary,
-    logX,
-    expY,
-  };
-
+  let chartProps = { ...props, code };
  return (
-    <div ref={observableRef}>
-      <SquiggleContainer>
-        <WrappedCodeEditor code={code} setCode={setCode} />
-        {result.tag === "Ok" ? (
-          <SquiggleItem
-            expression={result.value}
-            width={width}
-            height={200}
-            distributionPlotSettings={distributionPlotSettings}
-            showTypes={showTypes}
-            chartSettings={chartSettings}
-            environment={environment ?? defaultEnvironment}
-          />
-        ) : (
-          <SquiggleErrorAlert error={result.value} />
-        )}
-      </SquiggleContainer>
-    </div>
+    <SquiggleContainer>
+      <WrappedCodeEditor code={code} setCode={setCode} />
+      <SquiggleChart {...chartProps} />
+    </SquiggleContainer>
  );
 };

-export function renderSquiggleEditorToDom(props: SquiggleEditorProps) {
-  const parent = document.createElement("div");
-  ReactDOM.render(<SquiggleEditor {...props} />, parent);
-  return parent;
-}
-
 export interface SquigglePartialProps {
-  /** The input string for squiggle */
-  initialSquiggleString?: string;
+  /** The text inside the input (controlled) */
+  code?: string;
+  /** The default text inside the input (unControlled) */
+  defaultCode?: string;
  /** when the environment changes. Used again for notebook magic*/
  onChange?(expr: bindings | undefined): void;
+  /** When the code changes */
+  onCodeChange?(code: string): void;
  /** Previously declared variables */
  bindings?: bindings;
  /** If the output requires monte carlo sampling, the amount of samples */
@ -145,19 +61,21 @@ export interface SquigglePartialProps {
 }

 export const SquigglePartial: React.FC<SquigglePartialProps> = ({
-  initialSquiggleString = "",
+  code: controlledCode,
+  defaultCode = "",
  onChange,
+  onCodeChange,
  bindings = defaultBindings,
  environment,
  jsImports = defaultImports,
 }: SquigglePartialProps) => {
-  const [code, setCode] = useState(initialSquiggleString);
-  React.useEffect(
-    () => setCode(initialSquiggleString),
-    [initialSquiggleString]
-  );
+  const [code, setCode] = useMaybeControlledValue<string>({
+    value: controlledCode,
+    defaultValue: defaultCode,
+    onChange: onCodeChange,
+  });

-  const { result, observableRef } = useSquigglePartial({
+  const result = useSquigglePartial({
    code,
    bindings,
    environment,
@ -166,19 +84,9 @@ export const SquigglePartial: React.FC<SquigglePartialProps> = ({
  });

  return (
-    <div ref={observableRef}>
-      <SquiggleContainer>
-        <WrappedCodeEditor code={code} setCode={setCode} />
-        {result.tag !== "Ok" ? (
-          <SquiggleErrorAlert error={result.value} />
-        ) : null}
-      </SquiggleContainer>
-    </div>
+    <SquiggleContainer>
+      <WrappedCodeEditor code={code} setCode={setCode} />
+      {result.tag !== "Ok" ? <SquiggleErrorAlert error={result.value} /> : null}
+    </SquiggleContainer>
  );
 };
-
-export function renderSquigglePartialToDom(props: SquigglePartialProps) {
-  const parent = document.createElement("div");
-  ReactDOM.render(<SquigglePartial {...props} />, parent);
-  return parent;
-}
--- a/packages/components/src/components/SquigglePlayground.tsx
+++ b/packages/components/src/components/SquigglePlayground.tsx
@ -1,15 +1,18 @@
-import React, { FC, Fragment, useState, useEffect } from "react";
-import ReactDOM from "react-dom";
+import React, { FC, useState, useEffect, useMemo } from "react";
 import { Path, useForm, UseFormRegister, useWatch } from "react-hook-form";
 import * as yup from "yup";
+import { useMaybeControlledValue } from "../lib/hooks";
 import { yupResolver } from "@hookform/resolvers/yup";
-import { Tab } from "@headlessui/react";
 import {
  ChartSquareBarIcon,
+  CheckCircleIcon,
  CodeIcon,
  CogIcon,
  CurrencyDollarIcon,
  EyeIcon,
+  PauseIcon,
+  PlayIcon,
+  RefreshIcon,
 } from "@heroicons/react/solid";
 import clsx from "clsx";

@ -20,10 +23,13 @@ import { CodeEditor } from "./CodeEditor";
 import { JsonEditor } from "./JsonEditor";
 import { ErrorAlert, SuccessAlert } from "./Alert";
 import { SquiggleContainer } from "./SquiggleContainer";
+import { Toggle } from "./ui/Toggle";
+import { Checkbox } from "./ui/Checkbox";
+import { StyledTab } from "./ui/StyledTab";

 interface PlaygroundProps {
  /** The initial squiggle string to put in the playground */
-  initialSquiggleString?: string;
+  defaultCode?: string;
  /** How many pixels high is the playground */
  height?: number;
  /** Whether to show the types of outputs in the playground */
@ -44,104 +50,45 @@ interface PlaygroundProps {
  showEditor?: boolean;
 }

-const schema = yup
-  .object()
-  .shape({
-    sampleCount: yup
-      .number()
-      .required()
-      .positive()
-      .integer()
-      .default(1000)
-      .min(10)
-      .max(1000000),
-    xyPointLength: yup
-      .number()
-      .required()
-      .positive()
-      .integer()
-      .default(1000)
-      .min(10)
-      .max(10000),
-    chartHeight: yup.number().required().positive().integer().default(350),
-    leftSizePercent: yup
-      .number()
-      .required()
-      .positive()
-      .integer()
-      .min(10)
-      .max(100)
-      .default(50),
-    showTypes: yup.boolean(),
-    showControls: yup.boolean(),
-    showSummary: yup.boolean(),
-    showEditor: yup.boolean(),
-    logX: yup.boolean(),
-    expY: yup.boolean(),
-    showSettingsPage: yup.boolean().default(false),
-    diagramStart: yup
-      .number()
-      .required()
-      .positive()
-      .integer()
-      .default(0)
-      .min(0),
-    diagramStop: yup
-      .number()
-      .required()
-      .positive()
-      .integer()
-      .default(10)
-      .min(0),
-    diagramCount: yup
-      .number()
-      .required()
-      .positive()
-      .integer()
-      .default(20)
-      .min(2),
-  })
-  .required();
+const schema = yup.object({}).shape({
+  sampleCount: yup
+    .number()
+    .required()
+    .positive()
+    .integer()
+    .default(1000)
+    .min(10)
+    .max(1000000),
+  xyPointLength: yup
+    .number()
+    .required()
+    .positive()
+    .integer()
+    .default(1000)
+    .min(10)
+    .max(10000),
+  chartHeight: yup.number().required().positive().integer().default(350),
+  leftSizePercent: yup
+    .number()
+    .required()
+    .positive()
+    .integer()
+    .min(10)
+    .max(100)
+    .default(50),
+  showTypes: yup.boolean().required(),
+  showControls: yup.boolean().required(),
+  showSummary: yup.boolean().required(),
+  showEditor: yup.boolean().required(),
+  logX: yup.boolean().required(),
+  expY: yup.boolean().required(),
+  showSettingsPage: yup.boolean().default(false),
+  diagramStart: yup.number().required().positive().integer().default(0).min(0),
+  diagramStop: yup.number().required().positive().integer().default(10).min(0),
+  diagramCount: yup.number().required().positive().integer().default(20).min(2),
+});

-type StyledTabProps = {
-  name: string;
-  icon: (props: React.ComponentProps<"svg">) => JSX.Element;
-};
-
-const StyledTab: React.FC<StyledTabProps> = ({ name, icon: Icon }) => {
-  return (
-    <Tab key={name} as={Fragment}>
-      {({ selected }) => (
-        <button className="group flex rounded-md focus:outline-none focus-visible:ring-offset-gray-100">
-          <span
-            className={clsx(
-              "p-1 pl-2.5 pr-3.5 rounded-md flex items-center text-sm font-medium",
-              selected && "bg-white shadow-sm ring-1 ring-black ring-opacity-5"
-            )}
-          >
-            <Icon
-              className={clsx(
-                "-ml-0.5 mr-2 h-4 w-4",
-                selected
-                  ? "text-slate-500"
-                  : "text-gray-400 group-hover:text-gray-900"
-              )}
-            />
-            <span
-              className={clsx(
-                selected
-                  ? "text-gray-900"
-                  : "text-gray-600 group-hover:text-gray-900"
-              )}
-            >
-              {name}
-            </span>
-          </span>
-        </button>
-      )}
-    </Tab>
-  );
-};
+type FormFields = yup.InferType<typeof schema>;

 const HeadedSection: FC<{ title: string; children: React.ReactNode }> = ({
  title,
@ -182,30 +129,256 @@ function InputItem<T>({
  );
 }

-function Checkbox<T>({
-  name,
-  label,
+const SamplingSettings: React.FC<{ register: UseFormRegister<FormFields> }> = ({
  register,
-}: {
-  name: Path<T>;
-  label: string;
-  register: UseFormRegister<T>;
-}) {
-  return (
-    <label className="flex items-center">
-      <input
-        type="checkbox"
-        {...register(name)}
-        className="form-checkbox focus:ring-indigo-500 h-4 w-4 text-indigo-600 border-gray-300 rounded"
+}) => (
+  <div className="space-y-6 p-3 max-w-xl">
+    <div>
+      <InputItem
+        name="sampleCount"
+        type="number"
+        label="Sample Count"
+        register={register}
      />
-      {/* Clicking on the div makes the checkbox lose focus while mouse button is pressed, leading to annoying blinking; I couldn't figure out how to fix this. */}
-      <div className="ml-3 text-sm font-medium text-gray-700">{label}</div>
-    </label>
+      <div className="mt-2">
+        <Text>
+          How many samples to use for Monte Carlo simulations. This can
+          occasionally be overridden by specific Squiggle programs.
+        </Text>
+      </div>
+    </div>
+    <div>
+      <InputItem
+        name="xyPointLength"
+        type="number"
+        register={register}
+        label="Coordinate Count (For PointSet Shapes)"
+      />
+      <div className="mt-2">
+        <Text>
+          When distributions are converted into PointSet shapes, we need to know
+          how many coordinates to use.
+        </Text>
+      </div>
+    </div>
+  </div>
+);
+
+const ViewSettings: React.FC<{ register: UseFormRegister<FormFields> }> = ({
+  register,
+}) => (
+  <div className="space-y-6 p-3 divide-y divide-gray-200 max-w-xl">
+    <HeadedSection title="General Display Settings">
+      <div className="space-y-4">
+        <Checkbox
+          name="showEditor"
+          register={register}
+          label="Show code editor on left"
+        />
+        <InputItem
+          name="chartHeight"
+          type="number"
+          register={register}
+          label="Chart Height (in pixels)"
+        />
+        <Checkbox
+          name="showTypes"
+          register={register}
+          label="Show information about displayed types"
+        />
+      </div>
+    </HeadedSection>
+
+    <div className="pt-8">
+      <HeadedSection title="Distribution Display Settings">
+        <div className="space-y-2">
+          <Checkbox
+            register={register}
+            name="logX"
+            label="Show x scale logarithmically"
+          />
+          <Checkbox
+            register={register}
+            name="expY"
+            label="Show y scale exponentially"
+          />
+          <Checkbox
+            register={register}
+            name="showControls"
+            label="Show toggles to adjust scale of x and y axes"
+          />
+          <Checkbox
+            register={register}
+            name="showSummary"
+            label="Show summary statistics"
+          />
+        </div>
+      </HeadedSection>
+    </div>
+
+    <div className="pt-8">
+      <HeadedSection title="Function Display Settings">
+        <div className="space-y-6">
+          <Text>
+            When displaying functions of single variables that return numbers or
+            distributions, we need to use defaults for the x-axis. We need to
+            select a minimum and maximum value of x to sample, and a number n of
+            the number of points to sample.
+          </Text>
+          <div className="space-y-4">
+            <InputItem
+              type="number"
+              name="diagramStart"
+              register={register}
+              label="Min X Value"
+            />
+            <InputItem
+              type="number"
+              name="diagramStop"
+              register={register}
+              label="Max X Value"
+            />
+            <InputItem
+              type="number"
+              name="diagramCount"
+              register={register}
+              label="Points between X min and X max to sample"
+            />
+          </div>
+        </div>
+      </HeadedSection>
+    </div>
+  </div>
+);
+
+const InputVariablesSettings: React.FC<{
+  initialImports: any; // TODO - any json type
+  setImports: (imports: any) => void;
+}> = ({ initialImports, setImports }) => {
+  const [importString, setImportString] = useState(() =>
+    JSON.stringify(initialImports)
  );
-}
+  const [importsAreValid, setImportsAreValid] = useState(true);
+
+  const onChange = (value: string) => {
+    setImportString(value);
+    let imports = {} as any;
+    try {
+      imports = JSON.parse(value);
+      setImportsAreValid(true);
+    } catch (e) {
+      setImportsAreValid(false);
+    }
+    setImports(imports);
+  };
+
+  return (
+    <div className="p-3 max-w-3xl">
+      <HeadedSection title="Import Variables from JSON">
+        <div className="space-y-6">
+          <Text>
+            You can import variables from JSON into your Squiggle code.
+            Variables are accessed with dollar signs. For example, "timeNow"
+            would be accessed as "$timeNow".
+          </Text>
+          <div className="border border-slate-200 mt-6 mb-2">
+            <JsonEditor
+              value={importString}
+              onChange={onChange}
+              oneLine={false}
+              showGutter={true}
+              height={150}
+            />
+          </div>
+          <div className="p-1 pt-2">
+            {importsAreValid ? (
+              <SuccessAlert heading="Valid JSON" />
+            ) : (
+              <ErrorAlert heading="Invalid JSON">
+                You must use valid JSON in this editor.
+              </ErrorAlert>
+            )}
+          </div>
+        </div>
+      </HeadedSection>
+    </div>
+  );
+};
+
+const RunControls: React.FC<{
+  autorunMode: boolean;
+  isRunning: boolean;
+  isStale: boolean;
+  onAutorunModeChange: (value: boolean) => void;
+  run: () => void;
+}> = ({ autorunMode, isRunning, isStale, onAutorunModeChange, run }) => {
+  const CurrentPlayIcon = isRunning ? RefreshIcon : PlayIcon;
+
+  return (
+    <div className="flex space-x-1 items-center">
+      {autorunMode ? null : (
+        <button onClick={run}>
+          <CurrentPlayIcon
+            className={clsx(
+              "w-8 h-8",
+              isRunning && "animate-spin",
+              isStale ? "text-indigo-500" : "text-gray-400"
+            )}
+          />
+        </button>
+      )}
+      <Toggle
+        texts={["Autorun", "Paused"]}
+        icons={[CheckCircleIcon, PauseIcon]}
+        status={autorunMode}
+        onChange={onAutorunModeChange}
+      />
+    </div>
+  );
+};
+
+const useRunnerState = (code: string) => {
+  const [autorunMode, setAutorunMode] = useState(true);
+  const [renderedCode, setRenderedCode] = useState(code); // used in manual run mode only
+  const [isRunning, setIsRunning] = useState(false); // used in manual run mode only
+
+  // This part is tricky and fragile; we need to re-render first to make sure that the icon is spinning,
+  // and only then evaluate the squiggle code (which freezes the UI).
+  // Also note that `useEffect` execution order matters here.
+  // Hopefully it'll all go away after we make squiggle code evaluation async.
+  useEffect(() => {
+    if (renderedCode === code && isRunning) {
+      // It's not possible to put this after `setRenderedCode(code)` below because React would apply
+      // `setIsRunning` and `setRenderedCode` together and spinning icon will disappear immediately.
+      setIsRunning(false);
+    }
+  }, [renderedCode, code, isRunning]);
+
+  useEffect(() => {
+    if (!autorunMode && isRunning) {
+      setRenderedCode(code); // TODO - force run even if code hasn't changed
+    }
+  }, [autorunMode, code, isRunning]);
+
+  const run = () => {
+    // The rest will be handled by useEffects above, but we need to update the spinner first.
+    setIsRunning(true);
+  };
+
+  return {
+    run,
+    renderedCode: autorunMode ? code : renderedCode,
+    isRunning,
+    autorunMode,
+    setAutorunMode: (newValue: boolean) => {
+      if (!newValue) setRenderedCode(code);
+      setAutorunMode(newValue);
+    },
+  };
+};

 export const SquigglePlayground: FC<PlaygroundProps> = ({
-  initialSquiggleString = "",
+  defaultCode = "",
  height = 500,
  showTypes = false,
  showControls = false,
@ -217,12 +390,14 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
  onSettingsChange,
  showEditor = true,
 }) => {
-  const [uncontrolledCode, setUncontrolledCode] = useState(
-    initialSquiggleString
-  );
-  const [importString, setImportString] = useState("{}");
+  const [code, setCode] = useMaybeControlledValue({
+    value: controlledCode,
+    defaultValue: defaultCode,
+    onChange: onCodeChange,
+  });
+
  const [imports, setImports] = useState({});
-  const [importsAreValid, setImportsAreValid] = useState(true);
+
  const { register, control } = useForm({
    resolver: yupResolver(schema),
    defaultValues: {
@ -250,182 +425,24 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
    onSettingsChange?.(vars);
  }, [vars, onSettingsChange]);

-  const chartSettings = {
-    start: Number(vars.diagramStart),
-    stop: Number(vars.diagramStop),
-    count: Number(vars.diagramCount),
-  };
-  const env: environment = {
-    sampleCount: Number(vars.sampleCount),
-    xyPointLength: Number(vars.xyPointLength),
-  };
-  const getChangeJson = (r: string) => {
-    setImportString(r);
-    try {
-      setImports(JSON.parse(r));
-      setImportsAreValid(true);
-    } catch (e) {
-      setImportsAreValid(false);
-    }
-  };
-
-  const code = controlledCode ?? uncontrolledCode;
-
-  const samplingSettings = (
-    <div className="space-y-6 p-3 max-w-xl">
-      <div>
-        <InputItem
-          name="sampleCount"
-          type="number"
-          label="Sample Count"
-          register={register}
-        />
-        <div className="mt-2">
-          <Text>
-            How many samples to use for Monte Carlo simulations. This can
-            occasionally be overridden by specific Squiggle programs.
-          </Text>
-        </div>
-      </div>
-      <div>
-        <InputItem
-          name="xyPointLength"
-          type="number"
-          register={register}
-          label="Coordinate Count (For PointSet Shapes)"
-        />
-        <div className="mt-2">
-          <Text>
-            When distributions are converted into PointSet shapes, we need to
-            know how many coordinates to use.
-          </Text>
-        </div>
-      </div>
-    </div>
+  const env: environment = useMemo(
+    () => ({
+      sampleCount: Number(vars.sampleCount),
+      xyPointLength: Number(vars.xyPointLength),
+    }),
+    [vars.sampleCount, vars.xyPointLength]
  );

-  const viewSettings = (
-    <div className="space-y-6 p-3 divide-y divide-gray-200 max-w-xl">
-      <HeadedSection title="General Display Settings">
-        <div className="space-y-4">
-          <Checkbox
-            name="showEditor"
-            register={register}
-            label="Show code editor on left"
-          />
-          <InputItem
-            name="chartHeight"
-            type="number"
-            register={register}
-            label="Chart Height (in pixels)"
-          />
-          <Checkbox
-            name="showTypes"
-            register={register}
-            label="Show information about displayed types"
-          />
-        </div>
-      </HeadedSection>
-
-      <div className="pt-8">
-        <HeadedSection title="Distribution Display Settings">
-          <div className="space-y-2">
-            <Checkbox
-              register={register}
-              name="logX"
-              label="Show x scale logarithmically"
-            />
-            <Checkbox
-              register={register}
-              name="expY"
-              label="Show y scale exponentially"
-            />
-            <Checkbox
-              register={register}
-              name="showControls"
-              label="Show toggles to adjust scale of x and y axes"
-            />
-            <Checkbox
-              register={register}
-              name="showSummary"
-              label="Show summary statistics"
-            />
-          </div>
-        </HeadedSection>
-      </div>
-
-      <div className="pt-8">
-        <HeadedSection title="Function Display Settings">
-          <div className="space-y-6">
-            <Text>
-              When displaying functions of single variables that return numbers
-              or distributions, we need to use defaults for the x-axis. We need
-              to select a minimum and maximum value of x to sample, and a number
-              n of the number of points to sample.
-            </Text>
-            <div className="space-y-4">
-              <InputItem
-                type="number"
-                name="diagramStart"
-                register={register}
-                label="Min X Value"
-              />
-              <InputItem
-                type="number"
-                name="diagramStop"
-                register={register}
-                label="Max X Value"
-              />
-              <InputItem
-                type="number"
-                name="diagramCount"
-                register={register}
-                label="Points between X min and X max to sample"
-              />
-            </div>
-          </div>
-        </HeadedSection>
-      </div>
-    </div>
-  );
-
-  const inputVariableSettings = (
-    <div className="p-3 max-w-3xl">
-      <HeadedSection title="Import Variables from JSON">
-        <div className="space-y-6">
-          <Text>
-            You can import variables from JSON into your Squiggle code.
-            Variables are accessed with dollar signs. For example, "timeNow"
-            would be accessed as "$timeNow".
-          </Text>
-          <div className="border border-slate-200 mt-6 mb-2">
-            <JsonEditor
-              value={importString}
-              onChange={getChangeJson}
-              oneLine={false}
-              showGutter={true}
-              height={150}
-            />
-          </div>
-          <div className="p-1 pt-2">
-            {importsAreValid ? (
-              <SuccessAlert heading="Valid JSON" />
-            ) : (
-              <ErrorAlert heading="Invalid JSON">
-                You must use valid JSON in this editor.
-              </ErrorAlert>
-            )}
-          </div>
-        </div>
-      </HeadedSection>
-    </div>
-  );
+  const { run, autorunMode, setAutorunMode, isRunning, renderedCode } =
+    useRunnerState(code);

  const squiggleChart = (
    <SquiggleChart
-      squiggleString={code}
+      code={renderedCode}
      environment={env}
-      chartSettings={chartSettings}
+      diagramStart={Number(vars.diagramStart)}
+      diagramStop={Number(vars.diagramStop)}
+      diagramCount={Number(vars.diagramCount)}
      height={vars.chartHeight}
      showTypes={vars.showTypes}
      showControls={vars.showControls}
@ -441,13 +458,8 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
    <div className="border border-slate-200">
      <CodeEditor
        value={code}
-        onChange={(newCode) => {
-          if (controlledCode === undefined) {
-            // uncontrolled mode
-            setUncontrolledCode(newCode);
-          }
-          onCodeChange?.(newCode);
-        }}
+        onChange={setCode}
+        onSubmit={run}
        oneLine={false}
        showGutter={true}
        height={height - 1}
@ -458,12 +470,21 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({
  );

  const tabs = (
-    <Tab.Panels>
-      <Tab.Panel>{firstTab}</Tab.Panel>
-      <Tab.Panel>{samplingSettings}</Tab.Panel>
-      <Tab.Panel>{viewSettings}</Tab.Panel>
-      <Tab.Panel>{inputVariableSettings}</Tab.Panel>
-    </Tab.Panels>
+    <StyledTab.Panels>
+      <StyledTab.Panel>{firstTab}</StyledTab.Panel>
+      <StyledTab.Panel>
+        <SamplingSettings register={register} />
+      </StyledTab.Panel>
+      <StyledTab.Panel>
+        <ViewSettings register={register} />
+      </StyledTab.Panel>
+      <StyledTab.Panel>
+        <InputVariablesSettings
+          initialImports={imports}
+          setImports={setImports}
+        />
+      </StyledTab.Panel>
+    </StyledTab.Panels>
  );

  const withEditor = (
@ -477,26 +498,29 @@ export const SquigglePlayground: FC<PlaygroundProps> = ({

  return (
    <SquiggleContainer>
-      <Tab.Group>
+      <StyledTab.Group>
        <div className="pb-4">
-          <Tab.List className="flex w-fit p-0.5 mt-2 rounded-md bg-slate-100 hover:bg-slate-200">
-            <StyledTab
-              name={vars.showEditor ? "Code" : "Display"}
-              icon={vars.showEditor ? CodeIcon : EyeIcon}
+          <div className="flex justify-between items-center mt-2">
+            <StyledTab.List>
+              <StyledTab
+                name={vars.showEditor ? "Code" : "Display"}
+                icon={vars.showEditor ? CodeIcon : EyeIcon}
+              />
+              <StyledTab name="Sampling Settings" icon={CogIcon} />
+              <StyledTab name="View Settings" icon={ChartSquareBarIcon} />
+              <StyledTab name="Input Variables" icon={CurrencyDollarIcon} />
+            </StyledTab.List>
+            <RunControls
+              autorunMode={autorunMode}
+              isStale={renderedCode !== code}
+              run={run}
+              isRunning={isRunning}
+              onAutorunModeChange={setAutorunMode}
            />
-            <StyledTab name="Sampling Settings" icon={CogIcon} />
-            <StyledTab name="View Settings" icon={ChartSquareBarIcon} />
-            <StyledTab name="Input Variables" icon={CurrencyDollarIcon} />
-          </Tab.List>
+          </div>
          {vars.showEditor ? withEditor : withoutEditor}
        </div>
-      </Tab.Group>
+      </StyledTab.Group>
    </SquiggleContainer>
  );
 };
-
-export function renderSquigglePlaygroundToDom(props: PlaygroundProps) {
-  const parent = document.createElement("div");
-  ReactDOM.render(<SquigglePlayground {...props} />, parent);
-  return parent;
-}
--- a/packages/components/src/components/ui/Checkbox.tsx
+++ b/packages/components/src/components/ui/Checkbox.tsx
@ -0,0 +1,24 @@
+import React from "react";
+import { Path, UseFormRegister } from "react-hook-form";
+
+export function Checkbox<T>({
+  name,
+  label,
+  register,
+}: {
+  name: Path<T>;
+  label: string;
+  register: UseFormRegister<T>;
+}) {
+  return (
+    <label className="flex items-center">
+      <input
+        type="checkbox"
+        {...register(name)}
+        className="form-checkbox focus:ring-indigo-500 h-4 w-4 text-indigo-600 border-gray-300 rounded"
+      />
+      {/* Clicking on the div makes the checkbox lose focus while mouse button is pressed, leading to annoying blinking; I couldn't figure out how to fix this. */}
+      <div className="ml-3 text-sm font-medium text-gray-700">{label}</div>
+    </label>
+  );
+}
--- a/packages/components/src/components/ui/StyledTab.tsx
+++ b/packages/components/src/components/ui/StyledTab.tsx
@ -0,0 +1,60 @@
+import React, { Fragment } from "react";
+import { Tab } from "@headlessui/react";
+import clsx from "clsx";
+
+type StyledTabProps = {
+  name: string;
+  icon: (props: React.ComponentProps<"svg">) => JSX.Element;
+};
+
+type StyledTabType = React.FC<StyledTabProps> & {
+  List: React.FC<{ children: React.ReactNode }>;
+  Group: typeof Tab.Group;
+  Panels: typeof Tab.Panels;
+  Panel: typeof Tab.Panel;
+};
+
+export const StyledTab: StyledTabType = ({ name, icon: Icon }) => {
+  return (
+    <Tab as={Fragment}>
+      {({ selected }) => (
+        <button className="group flex rounded-md focus:outline-none focus-visible:ring-offset-gray-100">
+          <span
+            className={clsx(
+              "p-1 pl-2.5 pr-3.5 rounded-md flex items-center text-sm font-medium",
+              selected && "bg-white shadow-sm ring-1 ring-black ring-opacity-5"
+            )}
+          >
+            <Icon
+              className={clsx(
+                "-ml-0.5 mr-2 h-4 w-4",
+                selected
+                  ? "text-slate-500"
+                  : "text-gray-400 group-hover:text-gray-900"
+              )}
+            />
+            <span
+              className={clsx(
+                selected
+                  ? "text-gray-900"
+                  : "text-gray-600 group-hover:text-gray-900"
+              )}
+            >
+              {name}
+            </span>
+          </span>
+        </button>
+      )}
+    </Tab>
+  );
+};
+
+StyledTab.List = ({ children }) => (
+  <Tab.List className="flex w-fit p-0.5 rounded-md bg-slate-100 hover:bg-slate-200">
+    {children}
+  </Tab.List>
+);
+
+StyledTab.Group = Tab.Group;
+StyledTab.Panels = Tab.Panels;
+StyledTab.Panel = Tab.Panel;
--- a/packages/components/src/components/ui/Toggle.tsx
+++ b/packages/components/src/components/ui/Toggle.tsx
@ -0,0 +1,41 @@
+import clsx from "clsx";
+import { motion } from "framer-motion";
+import React from "react";
+
+type IconType = (props: React.ComponentProps<"svg">) => JSX.Element;
+
+type Props = {
+  status: boolean;
+  onChange: (status: boolean) => void;
+  texts: [string, string];
+  icons: [IconType, IconType];
+};
+
+export const Toggle: React.FC<Props> = ({
+  texts: [onText, offText],
+  icons: [OnIcon, OffIcon],
+  status,
+  onChange,
+}) => {
+  const CurrentIcon = status ? OnIcon : OffIcon;
+  return (
+    <motion.button
+      layout
+      transition={{ duration: 0.2 }}
+      className={clsx(
+        "rounded-full py-1 bg-indigo-500 text-white text-xs font-semibold flex items-center space-x-1",
+        status ? "bg-indigo-500" : "bg-gray-400",
+        status ? "pl-1 pr-3" : "pl-3 pr-1",
+        !status && "flex-row-reverse space-x-reverse"
+      )}
+      onClick={() => onChange(!status)}
+    >
+      <motion.div layout transition={{ duration: 0.2 }}>
+        <CurrentIcon className="w-6 h-6" />
+      </motion.div>
+      <motion.span layout transition={{ duration: 0.2 }}>
+        {status ? onText : offText}
+      </motion.span>
+    </motion.button>
+  );
+};
--- a/packages/components/src/index.ts
+++ b/packages/components/src/index.ts
@ -1,14 +1,6 @@
 export { SquiggleChart } from "./components/SquiggleChart";
-export {
-  SquiggleEditor,
-  SquigglePartial,
-  renderSquiggleEditorToDom,
-  renderSquigglePartialToDom,
-} from "./components/SquiggleEditor";
-export {
-  SquigglePlayground,
-  renderSquigglePlaygroundToDom,
-} from "./components/SquigglePlayground";
+export { SquiggleEditor, SquigglePartial } from "./components/SquiggleEditor";
+export { SquigglePlayground } from "./components/SquigglePlayground";
 export { SquiggleContainer } from "./components/SquiggleContainer";

 export { mergeBindings } from "@quri/squiggle-lang";
--- a/packages/components/src/lib/hooks.ts
+++ b/packages/components/src/lib/hooks.ts
@ -5,7 +5,7 @@ import {
  run,
  runPartial,
 } from "@quri/squiggle-lang";
-import { useEffect, useMemo, useRef } from "react";
+import { useEffect, useMemo, useState } from "react";

 type SquiggleArgs<T extends ReturnType<typeof run | typeof runPartial>> = {
  code: string;
@ -19,37 +19,18 @@ const useSquiggleAny = <T extends ReturnType<typeof run | typeof runPartial>>(
  args: SquiggleArgs<T>,
  f: (...args: Parameters<typeof run>) => T
 ) => {
-  //  We're using observable, where div elements can have a `value` property:
-  // https://observablehq.com/@observablehq/introduction-to-views
-  //
-  //  This is here to get the 'viewof' part of:
-  //  viewof env = cell('normal(0,1)')
-  //  to work
-  const ref = useRef<
-    HTMLDivElement & { value?: Extract<T, { tag: "Ok" }>["value"] }
-  >(null);
  const result: T = useMemo<T>(
    () => f(args.code, args.bindings, args.environment, args.jsImports),
    [f, args.code, args.bindings, args.environment, args.jsImports]
  );

-  useEffect(() => {
-    if (!ref.current) return;
-    ref.current.value = result.tag === "Ok" ? result.value : undefined;
-
-    ref.current.dispatchEvent(new CustomEvent("input"));
-  }, [result]);
-
  const { onChange } = args;

  useEffect(() => {
    onChange?.(result.tag === "Ok" ? result.value : undefined);
  }, [result, onChange]);

-  return {
-    result, // squiggleExpression or externalBindings
-    observableRef: ref, // can be passed to outermost <div> if you want to use your component as an observablehq's view
-  };
+  return result;
 };

 export const useSquigglePartial = (
@ -61,3 +42,23 @@ export const useSquigglePartial = (
 export const useSquiggle = (args: SquiggleArgs<ReturnType<typeof run>>) => {
  return useSquiggleAny(args, run);
 };
+
+type ControlledValueArgs<T> = {
+  value?: T;
+  defaultValue: T;
+  onChange?: (x: T) => void;
+};
+export function useMaybeControlledValue<T>(
+  args: ControlledValueArgs<T>
+): [T, (x: T) => void] {
+  let [uncontrolledValue, setUncontrolledValue] = useState(args.defaultValue);
+  let value = args.value ?? uncontrolledValue;
+  let onChange = (newValue: T) => {
+    if (args.value === undefined) {
+      // uncontrolled mode
+      setUncontrolledValue(newValue);
+    }
+    args.onChange?.(newValue);
+  };
+  return [value, onChange];
+}
--- a/packages/components/src/stories/SquiggleChart.stories.mdx
+++ b/packages/components/src/stories/SquiggleChart.stories.mdx
@ -29,7 +29,7 @@ could be continuous, discrete or mixed.
  <Story
    name="Continuous Symbolic"
    args={{
-      squiggleString: "normal(5,2)",
+      code: "normal(5,2)",
      width,
    }}
  >
@ -43,7 +43,7 @@ could be continuous, discrete or mixed.
  <Story
    name="Continuous Pointset"
    args={{
-      squiggleString: "toPointSet(normal(5,2))",
+      code: "toPointSet(normal(5,2))",
      width,
    }}
  >
@ -57,7 +57,7 @@ could be continuous, discrete or mixed.
  <Story
    name="Continuous SampleSet"
    args={{
-      squiggleString: "toSampleSet(normal(5,2), 1000)",
+      code: "toSampleSet(normal(5,2), 1000)",
      width,
    }}
  >
@ -71,7 +71,7 @@ could be continuous, discrete or mixed.
  <Story
    name="Discrete"
    args={{
-      squiggleString: "mx(0, 1, 3, 5, 8, 10, [0.1, 0.8, 0.5, 0.3, 0.2, 0.1])",
+      code: "mx(0, 1, 3, 5, 8, 10, [0.1, 0.8, 0.5, 0.3, 0.2, 0.1])",
      width,
    }}
  >
@ -85,8 +85,7 @@ could be continuous, discrete or mixed.
  <Story
    name="Mixed"
    args={{
-      squiggleString:
-        "mx(0, 1, 3, 5, 8, normal(8, 1), [0.1, 0.3, 0.4, 0.35, 0.2, 0.8])",
+      code: "mx(0, 1, 3, 5, 8, normal(8, 1), [0.1, 0.3, 0.4, 0.35, 0.2, 0.8])",
      width,
    }}
  >
@ -103,7 +102,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Constant"
    args={{
-      squiggleString: "500000000",
+      code: "500000000",
      width,
    }}
  >
@ -117,7 +116,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Array"
    args={{
-      squiggleString: "[normal(5,2), normal(10,1), normal(40,2), 400000]",
+      code: "[normal(5,2), normal(10,1), normal(40,2), 400000]",
      width,
    }}
  >
@ -131,7 +130,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Error"
    args={{
-      squiggleString: "f(x) = normal(",
+      code: "f(x) = normal(",
      width,
    }}
  >
@ -145,7 +144,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Boolean"
    args={{
-      squiggleString: "3 == 3",
+      code: "3 == 3",
      width,
    }}
  >
@ -159,7 +158,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Function to Distribution"
    args={{
-      squiggleString: "foo(t) = normal(t,2)*normal(5,3); foo",
+      code: "foo(t) = normal(t,2)*normal(5,3); foo",
      width,
    }}
  >
@ -173,7 +172,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Function to Number"
    args={{
-      squiggleString: "foo(t) = t^2; foo",
+      code: "foo(t) = t^2; foo",
      width,
    }}
  >
@ -187,7 +186,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="Record"
    args={{
-      squiggleString: "{foo: 35 to 50, bar: [1,2,3]}",
+      code: "{foo: 35 to 50, bar: [1,2,3]}",
      width,
    }}
  >
@ -201,7 +200,7 @@ to allow large and small numbers being printed cleanly.
  <Story
    name="String"
    args={{
-      squiggleString: '"Lucky day!"',
+      code: '"Lucky day!"',
      width,
    }}
  >
--- a/packages/components/src/stories/SquiggleEditor.stories.mdx
+++ b/packages/components/src/stories/SquiggleEditor.stories.mdx
@ -14,7 +14,20 @@ the distribution.
  <Story
    name="Normal"
    args={{
-      initialSquiggleString: "normal(5,2)",
+      defaultCode: "normal(5,2)",
+    }}
+  >
+    {Template.bind({})}
+  </Story>
+</Canvas>
+
+It's also possible to create a controlled version of the same component
+
+<Canvas>
+  <Story
+    name="Controlled"
+    args={{
+      code: "normal(5,2)",
    }}
  >
    {Template.bind({})}
@ -27,7 +40,7 @@ You can also name variables like so:
  <Story
    name="Variables"
    args={{
-      initialSquiggleString: "x = 2\nnormal(x,2)",
+      defaultCode: "x = 2\nnormal(x,2)",
    }}
  >
    {Template.bind({})}
--- a/packages/components/src/stories/SquigglePartial.stories.mdx
+++ b/packages/components/src/stories/SquigglePartial.stories.mdx
@ -15,7 +15,7 @@ instead returns bindings that can be used by further Squiggle Editors.
  <Story
    name="Standalone"
    args={{
-      initialSquiggleString: "x = normal(5,2)",
+      defaultCode: "x = normal(5,2)",
    }}
  >
    {Template.bind({})}
@ -36,12 +36,12 @@ instead returns bindings that can be used by further Squiggle Editors.
        <>
          <SquigglePartial
            {...props}
-            initialSquiggleString={props.initialPartialString}
+            defaultCode={props.initialPartialString}
            onChange={setBindings}
          />
          <SquiggleEditor
            {...props}
-            initialSquiggleString={props.initialEditorString}
+            defaultCode={props.initialEditorString}
            bindings={bindings}
          />
        </>
--- a/packages/components/src/stories/SquigglePlayground.stories.mdx
+++ b/packages/components/src/stories/SquigglePlayground.stories.mdx
@ -14,7 +14,7 @@ including sampling settings, in squiggle.
  <Story
    name="Normal"
    args={{
-      initialSquiggleString: "normal(5,2)",
+      defaultCode: "normal(5,2)",
      height: 800,
    }}
  >
--- a/packages/squiggle-lang/tests/Distributions/Symbolic_test.res
+++ b/packages/squiggle-lang/tests/Distributions/Symbolic_test.res
@ -77,6 +77,23 @@ describe("(Symbolic) mean", () => {
    meanValue->unpackFloat->expect->ExpectJs.toBeFalsy
  })

+  testAll(
+    "of beta distributions from mean and standard dev",
+    list{(0.39, 0.1), (0.08, 0.1), (0.8, 0.3)},
+    tup => {
+      let (mean, stdev) = tup
+      let betaDistribution = SymbolicDist.Beta.fromMeanAndStdev(mean, stdev)
+      let meanValue =
+        betaDistribution->E.R2.fmap(d =>
+          run(FromDist(ToFloat(#Mean), d->DistributionTypes.Symbolic))
+        )
+      switch meanValue {
+      | Ok(value) => value->unpackFloat->expect->toBeCloseTo(mean)
+      | Error(err) => err->expect->toBe("shouldn't happen")
+      }
+    },
+  )
+
  testAll(
    "of lognormal distributions",
    list{(2.0, 4.0), (1e-7, 1e-2), (-1e6, 10.0), (1e3, -1e2), (-1e8, -1e4), (1e2, 1e-5)},
--- a/packages/squiggle-lang/tests/Reducer/Reducer_Helpers.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_Helpers.res
@ -2,7 +2,7 @@
 module ErrorValue = Reducer_ErrorValue
 module ExternalExpressionValue = ReducerInterface.ExternalExpressionValue
 module InternalExpressionValue = ReducerInterface.InternalExpressionValue
-module Module = Reducer_Category_Module
+module Module = Reducer_Module

 let removeDefaultsInternal = (iev: InternalExpressionValue.t) => {
  switch iev {
--- a/packages/squiggle-lang/tests/Reducer/Reducer_Module/Reducer_Module_defineFFI_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_Module/Reducer_Module_defineFFI_test.res
@ -0,0 +1,100 @@
+module InternalExpressionValue = ReducerInterface_InternalExpressionValue
+module ExpressionT = Reducer_Expression_T
+module Module = Reducer_Module
+module Bindings = Reducer_Module
+module ErrorValue = Reducer_ErrorValue
+
+open Jest
+open Expect
+
+// ----------------------
+// --- Start of Module File
+// ----------------------
+
+module FooImplementation = {
+  // As this is a Rescript module, functions can use other functions in this module
+  // and in other stdLib modules implemented this way.
+  // Embedding function definitions in to switch statements is a bad practice
+  // - to reduce line count or to
+  let fooNumber = 0.0
+  let fooString = "Foo String"
+  let fooBool = true
+  let makeFoo = (a: string, b: string, _environment): string => `I am ${a}-foo and I am ${b}-foo`
+  let makeBar = (a: float, b: float, _environment): string =>
+    `I am ${a->Js.Float.toString}-bar and I am ${b->Js.Float.toString}-bar`
+}
+
+// There is a potential for type modules to define lift functions
+// for their own type to get rid of switch statements.
+module FooFFI = {
+  let makeFoo: ExpressionT.optionFfiFn = (args: array<InternalExpressionValue.t>, environment) => {
+    switch args {
+    | [IEvString(a), IEvString(b)] => FooImplementation.makeFoo(a, b, environment)->IEvString->Some
+    | _ => None
+    }
+  }
+  let makeBar: ExpressionT.optionFfiFn = (args: array<InternalExpressionValue.t>, environment) =>
+    switch args {
+    | [IEvNumber(a), IEvNumber(b)] => FooImplementation.makeBar(a, b, environment)->IEvString->Some
+    | _ => None
+    }
+}
+
+let fooModule: Module.t =
+  Module.emptyStdLib
+  ->Module.defineNumber("fooNumber", FooImplementation.fooNumber)
+  ->Module.defineString("fooString", FooImplementation.fooString)
+  ->Module.defineBool("fooBool", FooImplementation.fooBool)
+  ->Module.defineFunction("makeFoo", FooFFI.makeFoo)
+  ->Module.defineFunction("makeBar", FooFFI.makeBar)
+
+let makeBindings = (prevBindings: Bindings.t): Bindings.t =>
+  prevBindings->Module.defineModule("Foo", fooModule)
+
+// ----------------------
+// --- End of Module File
+// ----------------------
+
+let stdLibWithFoo = Bindings.emptyBindings->makeBindings
+let evalWithFoo = sourceCode =>
+  Reducer_Expression.parse(sourceCode)->Belt.Result.flatMap(expr =>
+    Reducer_Expression.reduceExpression(
+      expr,
+      stdLibWithFoo,
+      InternalExpressionValue.defaultEnvironment,
+    )
+  )
+let evalToStringResultWithFoo = sourceCode =>
+  evalWithFoo(sourceCode)->InternalExpressionValue.toStringResult
+
+describe("Module", () => {
+  test("fooNumber", () => {
+    let result = evalToStringResultWithFoo("Foo.fooNumber")
+    expect(result)->toEqual("Ok(0)")
+  })
+  test("fooString", () => {
+    let result = evalToStringResultWithFoo("Foo.fooString")
+    expect(result)->toEqual("Ok('Foo String')")
+  })
+  test("fooBool", () => {
+    let result = evalToStringResultWithFoo("Foo.fooBool")
+    expect(result)->toEqual("Ok(true)")
+  })
+  test("fooBool", () => {
+    let result = evalToStringResultWithFoo("Foo.fooBool")
+    expect(result)->toEqual("Ok(true)")
+  })
+  test("makeFoo", () => {
+    let result = evalToStringResultWithFoo("Foo.makeFoo('a', 'b')")
+    expect(result)->toEqual("Ok('I am a-foo and I am b-foo')")
+  })
+  test("makeFoo wrong arguments", () => {
+    let result = evalToStringResultWithFoo("Foo.makeFoo(1, 2)")
+    // Notice the error with types
+    expect(result)->toEqual("Error(Function not found: makeFoo(Number,Number))")
+  })
+  test("makeBar", () => {
+    let result = evalToStringResultWithFoo("Foo.makeBar(1, 2)")
+    expect(result)->toEqual("Ok('I am 1-bar and I am 2-bar')")
+  })
+})
--- a/packages/squiggle-lang/tests/Reducer/Reducer_TestMacroHelpers.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_TestMacroHelpers.res
@ -8,7 +8,7 @@ module InternalExpressionValue = ReducerInterface.InternalExpressionValue
 module ExpressionWithContext = Reducer_ExpressionWithContext
 module Macro = Reducer_Expression_Macro
 module T = Reducer_Expression_T
-module Module = Reducer_Category_Module
+module Module = Reducer_Module

 let testMacro_ = (
  tester,
--- a/packages/squiggle-lang/package.json
+++ b/packages/squiggle-lang/package.json
@ -42,7 +42,7 @@
    "@stdlib/stats": "^0.0.13",
    "jstat": "^1.9.5",
    "lodash": "^4.17.21",
-    "mathjs": "^10.6.3",
+    "mathjs": "^10.6.4",
    "pdfast": "^0.2.0"
  },
  "devDependencies": {
@ -65,7 +65,7 @@
    "rescript-fast-check": "^1.1.1",
    "ts-jest": "^27.1.4",
    "ts-loader": "^9.3.0",
-    "ts-node": "^10.8.1",
+    "ts-node": "^10.8.2",
    "typescript": "^4.7.4",
    "webpack": "^5.73.0",
    "webpack-cli": "^4.10.0"
--- a/packages/squiggle-lang/src/js/index.ts
+++ b/packages/squiggle-lang/src/js/index.ts
@ -172,6 +172,15 @@ function createTsExport(
      return tag("lambdaDeclaration", x.value);
    case "EvTypeIdentifier":
      return tag("typeIdentifier", x.value);
+    case "EvType":
+      let typeResult: tagged<"type", { [key: string]: squiggleExpression }> =
+        tag(
+          "type",
+          _.mapValues(x.value, (x: unknown) =>
+            convertRawToTypescript(x as rescriptExport, environment)
+          )
+        );
+      return typeResult;
    case "EvModule":
      let moduleResult: tagged<
        "module",
--- a/packages/squiggle-lang/src/js/rescript_interop.ts
+++ b/packages/squiggle-lang/src/js/rescript_interop.ts
@ -129,6 +129,7 @@ export type squiggleExpression =
  | tagged<"timeDuration", number>
  | tagged<"lambdaDeclaration", lambdaDeclaration>
  | tagged<"record", { [key: string]: squiggleExpression }>
+  | tagged<"type", { [key: string]: squiggleExpression }>
  | tagged<"typeIdentifier", string>
  | tagged<"module", { [key: string]: squiggleExpression }>;

--- a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
@ -124,6 +124,26 @@ module Beta = {
  let sample = (t: t) => Jstat.Beta.sample(t.alpha, t.beta)
  let mean = (t: t) => Ok(Jstat.Beta.mean(t.alpha, t.beta))
  let toString = ({alpha, beta}: t) => j`Beta($alpha,$beta)`
+
+  let fromMeanAndSampleSize = (mean, sampleSize) => {
+    // https://en.wikipedia.org/wiki/Beta_distribution#Mean_and_sample_size
+    let alpha = mean *. sampleSize
+    let beta = (1.0 -. mean) *. sampleSize
+    make(alpha, beta)
+  }
+
+  let fromMeanAndStdev = (mean, stdev) => {
+    // https://en.wikipedia.org/wiki/Beta_distribution#Mean_and_variance
+    if !(0.0 < stdev && stdev <= 0.5) {
+      Error("Stdev must be in in between 0 and 0.5.")
+    } else if !(0.0 <= mean && mean <= 1.0) {
+      Error("Mean must be in between 0 and 1.0.")
+    } else {
+      let var = stdev *. stdev
+      let sampleSize = mean *. (1.0 -. mean) /. var -. 1.0
+      fromMeanAndSampleSize(mean, sampleSize)
+    }
+  }
 }

 module Lognormal = {
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Library.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Library.res
@ -117,8 +117,12 @@ lognormal({mean: 5, stdev: 2})`,
  ),
  Function.make(
    ~name="Beta",
-    ~examples=`beta(20, 25)`,
-    ~definitions=[TwoArgDist.make("beta", twoArgs(SymbolicDist.Beta.make))],
+    ~examples=`beta(20, 25)
+beta({mean: 0.39, stdev: 0.1})`,
+    ~definitions=[
+      TwoArgDist.make("beta", twoArgs(SymbolicDist.Beta.make)),
+      TwoArgDist.makeRecordMeanStdev("beta", twoArgs(SymbolicDist.Beta.fromMeanAndStdev)),
+    ],
    (),
  ),
  Function.make(
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Category/Reducer_Category_Module_TypeChecker.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Category/Reducer_Category_Module_TypeChecker.res
@ -1,16 +0,0 @@
-module ExpressionValue = ReducerInterface_InternalExpressionValue
-module ExpressionT = Reducer_Expression_T
-open ExpressionValue
-
-let isOfResolvedType = (aType, aValue) => {
-  let caseTypeIdentifier = (aTypeIdentifier0, aValue) => {
-    let valueType = aValue->valueToValueType->valueTypeToString->Js.String2.toLowerCase
-    let aTypeIdentifier = aTypeIdentifier0->Js.String2.toLowerCase
-    aTypeIdentifier === valueType
-  }
-
-  switch aType {
-  | IEvTypeIdentifier(aTypeIdentifier) => caseTypeIdentifier(aTypeIdentifier, aValue)
-  | _ => false
-  }
-}
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn.res
@ -3,8 +3,9 @@ module ExpressionT = Reducer_Expression_T
 module ExternalLibrary = ReducerInterface.ExternalLibrary
 module Lambda = Reducer_Expression_Lambda
 module MathJs = Reducer_MathJs
-module Module = Reducer_Category_Module
+module Module = Reducer_Module
 module Result = Belt.Result
+module TypeBuilder = Reducer_Type_TypeBuilder
 open ReducerInterface_InternalExpressionValue
 open Reducer_ErrorValue

@ -166,59 +167,6 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
    )
  }

-  let typeModifier_memberOf = (aType, anArray) => {
-    let newRecord = Belt.Map.String.fromArray([
-      ("typeTag", IEvString("typeIdentifier")),
-      ("typeIdentifier", aType),
-    ])
-    newRecord->Belt.Map.String.set("memberOf", anArray)->IEvRecord->Ok
-  }
-  let typeModifier_memberOf_update = (aRecord, anArray) => {
-    aRecord->Belt.Map.String.set("memberOf", anArray)->IEvRecord->Ok
-  }
-
-  let typeModifier_min = (aType, value) => {
-    let newRecord = Belt.Map.String.fromArray([
-      ("typeTag", IEvString("typeIdentifier")),
-      ("typeIdentifier", aType),
-    ])
-    newRecord->Belt.Map.String.set("min", value)->IEvRecord->Ok
-  }
-  let typeModifier_min_update = (aRecord, value) => {
-    aRecord->Belt.Map.String.set("min", value)->IEvRecord->Ok
-  }
-
-  let typeModifier_max = (aType, value) => {
-    let newRecord = Belt.Map.String.fromArray([
-      ("typeTag", IEvString("typeIdentifier")),
-      ("typeIdentifier", aType),
-    ])
-    newRecord->Belt.Map.String.set("max", value)->IEvRecord->Ok
-  }
-  let typeModifier_max_update = (aRecord, value) =>
-    aRecord->Belt.Map.String.set("max", value)->IEvRecord->Ok
-
-  let typeModifier_opaque_update = aRecord =>
-    aRecord->Belt.Map.String.set("opaque", IEvBool(true))->IEvRecord->Ok
-
-  let typeOr = evArray => {
-    let newRecord = Belt.Map.String.fromArray([
-      ("typeTag", IEvString("typeOr")),
-      ("typeOr", evArray),
-    ])
-    newRecord->IEvRecord->Ok
-  }
-  let typeFunction = anArray => {
-    let output = Belt.Array.getUnsafe(anArray, Js.Array2.length(anArray) - 1)
-    let inputs = Js.Array2.slice(anArray, ~start=0, ~end_=-1)
-    let newRecord = Belt.Map.String.fromArray([
-      ("typeTag", IEvString("typeFunction")),
-      ("inputs", IEvArray(inputs)),
-      ("output", output),
-    ])
-    newRecord->IEvRecord->Ok
-  }
-
  switch call {
  | ("$_atIndex_$", [IEvArray(aValueArray), IEvNumber(fIndex)]) => arrayAtIndex(aValueArray, fIndex)
  | ("$_atIndex_$", [IEvModule(dict), IEvString(sIndex)]) => moduleAtIndex(dict, sIndex)
@ -233,20 +181,24 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
  | ("$_setTypeOfBindings_$", [IEvModule(nameSpace), IEvSymbol(symbol), value]) =>
    doSetTypeOfBindings(nameSpace, symbol, value)
  | ("$_typeModifier_memberOf_$", [IEvTypeIdentifier(typeIdentifier), IEvArray(arr)]) =>
-    typeModifier_memberOf(IEvTypeIdentifier(typeIdentifier), IEvArray(arr))
-  | ("$_typeModifier_memberOf_$", [IEvRecord(typeRecord), IEvArray(arr)]) =>
-    typeModifier_memberOf_update(typeRecord, IEvArray(arr))
+    TypeBuilder.typeModifier_memberOf(IEvTypeIdentifier(typeIdentifier), IEvArray(arr))
+  | ("$_typeModifier_memberOf_$", [IEvType(typeRecord), IEvArray(arr)]) =>
+    TypeBuilder.typeModifier_memberOf_update(typeRecord, IEvArray(arr))
  | ("$_typeModifier_min_$", [IEvTypeIdentifier(typeIdentifier), value]) =>
-    typeModifier_min(IEvTypeIdentifier(typeIdentifier), value)
-  | ("$_typeModifier_min_$", [IEvRecord(typeRecord), value]) =>
-    typeModifier_min_update(typeRecord, value)
+    TypeBuilder.typeModifier_min(IEvTypeIdentifier(typeIdentifier), value)
+  | ("$_typeModifier_min_$", [IEvType(typeRecord), value]) =>
+    TypeBuilder.typeModifier_min_update(typeRecord, value)
  | ("$_typeModifier_max_$", [IEvTypeIdentifier(typeIdentifier), value]) =>
-    typeModifier_max(IEvTypeIdentifier(typeIdentifier), value)
-  | ("$_typeModifier_max_$", [IEvRecord(typeRecord), value]) =>
-    typeModifier_max_update(typeRecord, value)
-  | ("$_typeModifier_opaque_$", [IEvRecord(typeRecord)]) => typeModifier_opaque_update(typeRecord)
-  | ("$_typeOr_$", [IEvArray(arr)]) => typeOr(IEvArray(arr))
-  | ("$_typeFunction_$", [IEvArray(arr)]) => typeFunction(arr)
+    TypeBuilder.typeModifier_max(IEvTypeIdentifier(typeIdentifier), value)
+  | ("$_typeModifier_max_$", [IEvType(typeRecord), value]) =>
+    TypeBuilder.typeModifier_max_update(typeRecord, value)
+  | ("$_typeModifier_opaque_$", [IEvType(typeRecord)]) =>
+    TypeBuilder.typeModifier_opaque_update(typeRecord)
+  | ("$_typeOr_$", [IEvArray(arr)]) => TypeBuilder.typeOr(IEvArray(arr))
+  | ("$_typeFunction_$", [IEvArray(arr)]) => TypeBuilder.typeFunction(arr)
+  | ("$_typeTuple_$", [IEvArray(elems)]) => TypeBuilder.typeTuple(elems)
+  | ("$_typeArray_$", [elem]) => TypeBuilder.typeArray(elem)
+  | ("$_typeRecord_$", [IEvArray(arrayOfPairs)]) => TypeBuilder.typeRecord(arrayOfPairs)
  | ("concat", [IEvArray(aValueArray), IEvArray(bValueArray)]) =>
    doAddArray(aValueArray, bValueArray)
  | ("concat", [IEvString(aValueString), IEvString(bValueString)]) =>
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
@ -9,7 +9,7 @@ module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
 module ExpressionT = Reducer_Expression_T
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module ExpressionWithContext = Reducer_ExpressionWithContext
-module Module = Reducer_Category_Module
+module Module = Reducer_Module
 module Result = Belt.Result
 open Reducer_Expression_ExpressionBuilder

--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Exception.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Exception.res
@ -0,0 +1,3 @@
+// There are switch stament cases in the code which are impossible to reach by design.
+// ImpossibleException is a sign of programming error.
+exception ImpossibleException
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
@ -6,7 +6,7 @@ module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module Lambda = Reducer_Expression_Lambda
 module Macro = Reducer_Expression_Macro
 module MathJs = Reducer_MathJs
-module Module = Reducer_Category_Module
+module Module = Reducer_Module
 module Result = Belt.Result
 module T = Reducer_Expression_T

--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
@ -3,7 +3,7 @@ module ErrorValue = Reducer_ErrorValue
 module ExpressionT = Reducer_Expression_T
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module Result = Belt.Result
-module Module = Reducer_Category_Module
+module Module = Reducer_Module

 type bindings = ExpressionT.bindings
 type context = bindings
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_BindingsReplacer.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_BindingsReplacer.res
@ -2,7 +2,7 @@ module ErrorValue = Reducer_ErrorValue
 module ExpressionT = Reducer_Expression_T
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module Result = Belt.Result
-module Module = Reducer_Category_Module
+module Module = Reducer_Module

 type errorValue = Reducer_ErrorValue.errorValue
 type expression = ExpressionT.expression
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
@ -2,7 +2,7 @@ module BBindingsReplacer = Reducer_Expression_BindingsReplacer
 module BErrorValue = Reducer_ErrorValue
 module BExpressionT = Reducer_Expression_T
 module BInternalExpressionValue = ReducerInterface_InternalExpressionValue
-module BModule = Reducer_Category_Module
+module BModule = Reducer_Module

 type errorValue = BErrorValue.errorValue
 type expression = BExpressionT.expression
@ -10,8 +10,6 @@ type expressionOrFFI = BExpressionT.expressionOrFFI
 type ffiFn = BExpressionT.ffiFn
 type internalCode = ReducerInterface_InternalExpressionValue.internalCode

-external castExpressionToInternalCode: expressionOrFFI => internalCode = "%identity"
-
 let eArray = anArray => anArray->BInternalExpressionValue.IEvArray->BExpressionT.EValue

 let eArrayString = anArray => anArray->BInternalExpressionValue.IEvArrayString->BExpressionT.EValue
@ -37,17 +35,12 @@ let eLambda = (
  BInternalExpressionValue.IEvLambda({
    parameters: parameters,
    context: context,
-    body: NotFFI(expr)->castExpressionToInternalCode,
+    body: NotFFI(expr)->BModule.castExpressionToInternalCode,
  })->BExpressionT.EValue
 }

-let eLambdaFFI = (parameters: array<string>, ffiFn: ffiFn) => {
-  let context = BModule.emptyModule
-  BInternalExpressionValue.IEvLambda({
-    parameters: parameters,
-    context: context,
-    body: FFI(ffiFn)->castExpressionToInternalCode,
-  })->BExpressionT.EValue
+let eLambdaFFI = (ffiFn: ffiFn) => {
+  ffiFn->BModule.eLambdaFFIValue->BExpressionT.EValue
 }

 let eNumber = aNumber => aNumber->BInternalExpressionValue.IEvNumber->BExpressionT.EValue
@ -81,6 +74,9 @@ let eBindExpression = (bindingExpr: expression, expression: expression): express
 let eBindExpressionDefault = (expression: expression): expression =>
  eFunction("$$_bindExpression_$$", list{expression})

+let eTernary = (truth: expression, trueCase: expression, falseCase: expression): expression =>
+  eFunction("$$_ternary_$$", list{truth, trueCase, falseCase})
+
 let eIdentifier = (name: string): expression =>
  name->BInternalExpressionValue.IEvSymbol->BExpressionT.EValue

--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
@ -3,14 +3,13 @@ module ErrorValue = Reducer_ErrorValue
 module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
 module ExpressionT = Reducer_Expression_T
 module ExpressionValue = ReducerInterface_InternalExpressionValue
-module Module = Reducer_Category_Module
+module Module = Reducer_Module
 module Result = Belt.Result

 type environment = ReducerInterface_InternalExpressionValue.environment
 type expression = ExpressionT.expression
 type expressionOrFFI = ExpressionT.expressionOrFFI
 type internalExpressionValue = ReducerInterface_InternalExpressionValue.t
-// type tmpExternalBindings = ReducerInterface_InternalExpressionValue.tmpExternalBindings
 type internalCode = ReducerInterface_InternalExpressionValue.internalCode

 external castInternalCodeToExpression: internalCode => expressionOrFFI = "%identity"
@ -19,12 +18,19 @@ let checkArity = (
  lambdaValue: ExpressionValue.lambdaValue,
  args: list<internalExpressionValue>,
 ) => {
-  let argsLength = Belt.List.length(args)
-  let parametersLength = Js.Array2.length(lambdaValue.parameters)
-  if argsLength !== parametersLength {
-    ErrorValue.REArityError(None, parametersLength, argsLength)->Error
-  } else {
-    args->Ok
+  let reallyCheck = {
+    let argsLength = Belt.List.length(args)
+    let parametersLength = Js.Array2.length(lambdaValue.parameters)
+    if argsLength !== parametersLength {
+      ErrorValue.REArityError(None, parametersLength, argsLength)->Error
+    } else {
+      args->Ok
+    }
+  }
+  let exprOrFFI = castInternalCodeToExpression(lambdaValue.body)
+  switch exprOrFFI {
+  | NotFFI(_) => reallyCheck
+  | FFI(_) => args->Ok
  }
 }

--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res
@ -71,6 +71,8 @@ type ffiFn = (
  environment,
 ) => result<internalExpressionValue, Reducer_ErrorValue.errorValue>

+type optionFfiFn = (array<internalExpressionValue>, environment) => option<internalExpressionValue>
+
 type expressionOrFFI =
  | NotFFI(expression)
  | FFI(ffiFn)
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Category/Reducer_Category_Module.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Category/Reducer_Category_Module.res
@ -1,5 +1,8 @@
 module ExpressionT = Reducer_Expression_T
+module InternalExpressionValue = ReducerInterface_InternalExpressionValue
+open Reducer_ErrorValue
 open ReducerInterface_InternalExpressionValue
+
 let expressionValueToString = toString

 type t = ReducerInterface_InternalExpressionValue.nameSpace
@ -66,7 +69,8 @@ let set = (nameSpace: t, id: string, value): t => {
  Belt.Map.String.set(container, id, value)->NameSpace
 }

-let emptyModule: t = NameSpace(Belt.Map.String.empty)
+let emptyModule: t = NameSpace(emptyMap)
+let emptyBindings = emptyModule

 let fromTypeScriptBindings = ReducerInterface_InternalExpressionValue.nameSpaceFromTypeScriptBindings
 let toTypeScriptBindings = ReducerInterface_InternalExpressionValue.nameSpaceToTypeScriptBindings
@ -100,13 +104,59 @@ let removeOther = (nameSpace: t, other: t): t => {
  })->NameSpace
 }

+external castExpressionToInternalCode: ExpressionT.expressionOrFFI => internalCode = "%identity"
+let eLambdaFFIValue = (ffiFn: ExpressionT.ffiFn) => {
+  IEvLambda({
+    parameters: [],
+    context: emptyModule,
+    body: FFI(ffiFn)->castExpressionToInternalCode,
+  })
+}
+
+let functionNotFoundError = (call: functionCall) =>
+  REFunctionNotFound(call->functionCallToCallSignature->functionCallSignatureToString)->Error
+
+let functionNotFoundErrorFFIFn = (functionName: string): ExpressionT.ffiFn => {
+  (args: array<internalExpressionValue>, _environment: environment): result<
+    internalExpressionValue,
+    errorValue,
+  > => {
+    let call = (functionName, args)
+    functionNotFoundError(call)
+  }
+}
+
+let convertOptionToFfiFn = (
+  myFunctionName: string,
+  myFunction: ExpressionT.optionFfiFn,
+): ExpressionT.ffiFn => {
+  (args: array<InternalExpressionValue.t>, environment) => {
+    myFunction(args, environment)
+    ->Belt.Option.map(v => v->Ok)
+    ->Belt.Option.getWithDefault(functionNotFoundErrorFFIFn(myFunctionName)(args, environment))
+  }
+}
+
 // -- Module definition
 let define = (nameSpace: t, identifier: string, ev: internalExpressionValue): t => {
  let NameSpace(container) = nameSpace
-  Belt.Map.String.set(container, identifier, ev)->NameSpace // TODO build lambda for polymorphic functions here
+  Belt.Map.String.set(container, identifier, ev)->NameSpace
 }
+
 let defineNumber = (nameSpace: t, identifier: string, value: float): t =>
  nameSpace->define(identifier, IEvNumber(value))

+let defineString = (nameSpace: t, identifier: string, value: string): t =>
+  nameSpace->define(identifier, IEvString(value))
+
+let defineBool = (nameSpace: t, identifier: string, value: bool): t =>
+  nameSpace->define(identifier, IEvBool(value))
+
 let defineModule = (nameSpace: t, identifier: string, value: t): t =>
  nameSpace->define(identifier, toExpressionValue(value))
+
+let defineFunction = (nameSpace: t, identifier: string, value: ExpressionT.optionFfiFn): t => {
+  nameSpace->define(identifier, convertOptionToFfiFn(identifier, value)->eLambdaFFIValue)
+}
+
+let emptyStdLib: t = emptyModule->defineBool("stdlib", true)
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Module/Reducer_Module_Lambda.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Module/Reducer_Module_Lambda.res
@ -0,0 +1,14 @@
+module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
+module ExpressionT = Reducer_Expression_T
+
+type expression = ExpressionT.expression
+
+let defaultCaseFFI = (functionName: string): expression => {
+  ExpressionBuilder.eLambdaFFI(Reducer_Module.functionNotFoundErrorFFIFn(functionName))
+}
+
+let addGuard = (
+  guard: expression,
+  expression: expression,
+  previousExpression: expression,
+): expression => ExpressionBuilder.eTernary(guard, expression, previousExpression)
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_GeneratedParser.peggy
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_GeneratedParser.peggy
@ -154,9 +154,7 @@ unary
  unaryOperator "unary operator"
  = ('-' / '.-' / '!' ) 

-postOperator = indexedValue
-
-indexedValue
+postOperator
  = collectionElement
  / atom

@ -343,11 +341,18 @@ typeModifierExpression = head:basicType tail:(_ '<-' _nl @typeModifier)*
    / modifier:identifier _ noArguments
      { return {modifier: modifier, args: []}; }
  
-basicType = typeConstructor / typeArray / typeRecord / typeInParanthesis / typeIdentifier
+basicType = typeConstructor / typeArray / typeTuple / typeRecord / typeInParanthesis / typeIdentifier

 typeArray = '[' _nl elem:typeExpression _nl ']' 
  {return h.apply('$_typeArray_$', elem)}

+typeTuple = '[' _nl elems:array_typeTupleArguments _nl ']' 
+  { return h.apply('$_typeTuple_$', h.constructArray(elems))}
+
+  array_typeTupleArguments
+    = head:typeExpression tail:(_ ',' _nl @typeExpression)* 
+    { return [head, ...tail]; }
+
 typeRecord = '{' _nl elems:array_typeRecordArguments _nl '}' 
  { return h.apply('$_typeRecord_$', h.constructRecord(elems)); }  

@ -375,9 +380,3 @@ typeOfStatement = identifier:identifier _ ':' _nl typeExpression:typeExpression
  { return h.makeFunctionCall('$_typeOf_$', [identifier, typeExpression])}

 typeInParanthesis = '(' _nl typeExpression:typeExpression _nl ')' {return typeExpression}
-
-// TODO: min max example
-// TODO: Example of foo = {a: 2, b: 5}; type fooKeys = string $ memberOf(foo->keys)
-// TODO: Example of memberOf( [1,2,3] )
-// TODO: Example of $ 
-// TODO: Cons(a, list) | EmptyList
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res
@ -5,7 +5,11 @@ type node = {"type": string}

@module("./Reducer_Peggy_GeneratedParser.js") external parse__: string => node = "parse"

-let syntaxErrorToLocation: Js.Exn.t => Reducer_ErrorValue.location = error => %raw(`error.location`)
+type withLocation = {"location": Reducer_ErrorValue.location}
+external castWithLocation: Js.Exn.t => withLocation = "%identity"
+
+let syntaxErrorToLocation = (error: Js.Exn.t): Reducer_ErrorValue.location =>
+  castWithLocation(error)["location"]

@genType
 let parse = (expr: string): result<node, errorValue> =>
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_T.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_T.res
@ -0,0 +1,82 @@
+module InternalExpressionValue = ReducerInterface_InternalExpressionValue
+open InternalExpressionValue
+
+type rec iType =
+  | ItTypeIdentifier(string)
+  | ItModifiedType({modifiedType: iType})
+  | ItTypeOr({typeOr: array<iType>})
+  | ItTypeFunction({inputs: array<iType>, output: iType})
+  | ItTypeArray({element: iType})
+  | ItTypeTuple({elements: array<iType>})
+  | ItTypeRecord({properties: Belt.Map.String.t<iType>})
+
+let rec fromTypeMap = typeMap => {
+  let default = IEvString("")
+  let evTypeTag: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "typeTag",
+    default,
+  )
+  let evTypeIdentifier: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "typeIdentifier",
+    default,
+  )
+  let evTypeOr: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "typeOr",
+    default,
+  )
+  let evInputs: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "inputs",
+    default,
+  )
+  let evOutput: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "output",
+    default,
+  )
+  let evElement: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "element",
+    default,
+  )
+  let evElements: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "elements",
+    default,
+  )
+  let evProperties: InternalExpressionValue.t = Belt.Map.String.getWithDefault(
+    typeMap,
+    "properties",
+    default,
+  )
+  //TODO: map type modifiers
+  switch evTypeTag {
+  | IEvString("typeIdentifier") => ItModifiedType({modifiedType: fromIEvValue(evTypeIdentifier)})
+  | IEvString("typeOr") => ItTypeOr({typeOr: fromIEvArray(evTypeOr)})
+  | IEvString("typeFunction") =>
+    ItTypeFunction({inputs: fromIEvArray(evInputs), output: fromIEvValue(evOutput)})
+  | IEvString("typeArray") => ItTypeArray({element: fromIEvValue(evElement)})
+  | IEvString("typeTuple") => ItTypeTuple({elements: fromIEvArray(evElements)})
+  | IEvString("typeRecord") => ItTypeRecord({properties: fromIEvRecord(evProperties)})
+  | _ => raise(Reducer_Exception.ImpossibleException)
+  }
+}
+and fromIEvValue = (ievValue: InternalExpressionValue.t) =>
+  switch ievValue {
+  | IEvTypeIdentifier(typeIdentifier) => ItTypeIdentifier({typeIdentifier})
+  | IEvType(typeMap) => fromTypeMap(typeMap)
+  | _ => raise(Reducer_Exception.ImpossibleException)
+  }
+and fromIEvArray = (ievArray: InternalExpressionValue.t) =>
+  switch ievArray {
+  | IEvArray(array) => array->Belt.Array.map(fromIEvValue)
+  | _ => raise(Reducer_Exception.ImpossibleException)
+  }
+and fromIEvRecord = (ievRecord: InternalExpressionValue.t) =>
+  switch ievRecord {
+  | IEvRecord(record) => record->Belt.Map.String.map(fromIEvValue)
+  | _ => raise(Reducer_Exception.ImpossibleException)
+  }
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_TypeBuilder.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_TypeBuilder.res
@ -0,0 +1,88 @@
+open ReducerInterface_InternalExpressionValue
+
+let typeModifier_memberOf = (aType, anArray) => {
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeIdentifier")),
+    ("typeIdentifier", aType),
+  ])
+  newRecord->Belt.Map.String.set("memberOf", anArray)->IEvType->Ok
+}
+
+let typeModifier_memberOf_update = (aRecord, anArray) => {
+  aRecord->Belt.Map.String.set("memberOf", anArray)->IEvType->Ok
+}
+
+let typeModifier_min = (aType, value) => {
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeIdentifier")),
+    ("typeIdentifier", aType),
+  ])
+  newRecord->Belt.Map.String.set("min", value)->IEvType->Ok
+}
+
+let typeModifier_min_update = (aRecord, value) => {
+  aRecord->Belt.Map.String.set("min", value)->IEvType->Ok
+}
+
+let typeModifier_max = (aType, value) => {
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeIdentifier")),
+    ("typeIdentifier", aType),
+  ])
+  newRecord->Belt.Map.String.set("max", value)->IEvType->Ok
+}
+
+let typeModifier_max_update = (aRecord, value) =>
+  aRecord->Belt.Map.String.set("max", value)->IEvType->Ok
+
+let typeModifier_opaque_update = aRecord =>
+  aRecord->Belt.Map.String.set("opaque", IEvBool(true))->IEvType->Ok
+
+let typeOr = evArray => {
+  let newRecord = Belt.Map.String.fromArray([("typeTag", IEvString("typeOr")), ("typeOr", evArray)])
+  newRecord->IEvType->Ok
+}
+
+let typeFunction = anArray => {
+  let output = Belt.Array.getUnsafe(anArray, Js.Array2.length(anArray) - 1)
+  let inputs = Js.Array2.slice(anArray, ~start=0, ~end_=-1)
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeFunction")),
+    ("inputs", IEvArray(inputs)),
+    ("output", output),
+  ])
+  newRecord->IEvType->Ok
+}
+
+let typeArray = element => {
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeTuple")),
+    ("element", element),
+  ])
+  newRecord->IEvType->Ok
+}
+
+let typeTuple = anArray => {
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeArray")),
+    ("elements", IEvArray(anArray)),
+  ])
+  newRecord->IEvType->Ok
+}
+
+let typeRecord = arrayOfPairs => {
+  let newProperties =
+    Belt.Array.map(arrayOfPairs, pairValue =>
+      switch pairValue {
+      | IEvArray([IEvString(key), valueValue]) => (key, valueValue)
+      | _ => ("wrong key type", pairValue->toStringWithType->IEvString)
+      }
+    )
+    ->Belt.Map.String.fromArray
+    ->IEvRecord
+  let newRecord = Belt.Map.String.fromArray([
+    ("typeTag", IEvString("typeRecord")),
+    ("properties", newProperties),
+  ])
+  newRecord->IEvType->Ok
+}
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_TypeChecker.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_TypeChecker.res
@ -0,0 +1,81 @@
+module ExpressionT = Reducer_Expression_T
+module InternalExpressionValue = ReducerInterface_InternalExpressionValue
+module T = Reducer_Type_T
+module TypeBuilder = Reducer_Type_TypeBuilder
+open InternalExpressionValue
+
+type typeErrorValue =
+  | TypeError(T.iType, InternalExpressionValue.t)
+  | TypeErrorWithPosition(T.iType, InternalExpressionValue.t, int)
+  | TypeErrorWithProperty(T.iType, InternalExpressionValue.t, string)
+
+let rec isOfResolvedIType = (anIType: T.iType, aValue): result<bool, typeErrorValue> => {
+  let caseTypeIdentifier = (anUpperTypeName, aValue) => {
+    let aTypeName = anUpperTypeName->Js.String2.toLowerCase
+    let valueTypeName = aValue->valueToValueType->valueTypeToString->Js.String2.toLowerCase
+    switch aTypeName === valueTypeName {
+    | true => Ok(true)
+    | false => TypeError(anIType, aValue)->Error
+    }
+  }
+
+  let _caseRecord = (anIType, evValue, propertyMap, map) => {
+    Belt.Map.String.reduce(propertyMap, Ok(true), (acc, property, propertyType) => {
+      Belt.Result.flatMap(acc, _ =>
+        switch Belt.Map.String.get(map, property) {
+        | Some(propertyValue) => isOfResolvedIType(propertyType, propertyValue)
+        | None => TypeErrorWithProperty(anIType, evValue, property)->Error
+        }
+      )
+    })
+  }
+  let _caseArray = (anIType, evValue, elementType, anArray) => {
+    Belt.Array.reduceWithIndex(anArray, Ok(true), (acc, element, index) => {
+      switch isOfResolvedIType(elementType, element) {
+      | Ok(_) => acc
+      | Error(_) => TypeErrorWithPosition(anIType, evValue, index)->Error
+      }
+    })
+  }
+
+  switch anIType {
+  | ItTypeIdentifier(name) => caseTypeIdentifier(name, aValue)
+  // TODO: Work in progress. Code is commented to make an a release of other features
+  // | ItModifiedType({modifiedType: anIType}) => raise(Reducer_Exception.ImpossibleException)
+  // | ItTypeOr({typeOr: anITypeArray}) => raise(Reducer_Exception.ImpossibleException)
+  // | ItTypeFunction({inputs: anITypeArray, output: anIType}) =>
+  //   raise(Reducer_Exception.ImpossibleException)
+  // | ItTypeArray({element: anIType}) => raise(Reducer_Exception.ImpossibleException)
+  // | ItTypeTuple({elements: anITypeArray}) => raise(Reducer_Exception.ImpossibleException)
+  // | ItTypeRecord({properties: anITypeMap}) => raise(Reducer_Exception.ImpossibleException)
+  | _ => raise(Reducer_Exception.ImpossibleException)
+  }
+}
+
+let isOfResolvedType = (aType: InternalExpressionValue.t, aValue): result<bool, typeErrorValue> =>
+  aType->T.fromIEvValue->isOfResolvedIType(aValue)
+
+// TODO: Work in progress. Code is commented to make an a release of other features
+// let checkArguments = (
+//   evFunctionType: InternalExpressionValue.t,
+//   args: array<InternalExpressionValue.t>,
+// ) => {
+//   let functionType = switch evFunctionType {
+//   | IEvRecord(functionType) => functionType
+//   | _ => raise(Reducer_Exception.ImpossibleException)
+//   }
+//   let evInputs = functionType->Belt.Map.String.getWithDefault("inputs", []->IEvArray)
+//   let inputs = switch evInputs {
+//   | IEvArray(inputs) => inputs
+//   | _ => raise(Reducer_Exception.ImpossibleException)
+//   }
+//   let rTupleType = TypeBuilder.typeTuple(inputs)
+//   Belt.Result.flatMap(rTupleType, tuppleType => isOfResolvedType(tuppleType, args->IEvArray))
+// }
+
+// let compileTypeExpression = (typeExpression: string, bindings: ExpressionT.bindings, reducerFn: ExpressionT.reducerFn) => {
+//     statement = `type compiled=${typeExpression}`
+
+// }
+
+//TODO: asGuard
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalExpressionValue.res
@ -24,6 +24,7 @@ type rec externalExpressionValue =
  | EvDeclaration(lambdaDeclaration)
  | EvTypeIdentifier(string)
  | EvModule(record)
+  | EvType(record)
 and record = Js.Dict.t<externalExpressionValue>
 and externalBindings = record
 and lambdaValue = {
@ -50,17 +51,18 @@ let rec toString = aValue =>
    }
  | EvBool(aBool) => Js.String.make(aBool)
  | EvCall(fName) => `:${fName}`
+  | EvDate(date) => DateTime.Date.toString(date)
+  | EvDeclaration(d) => Declaration.toString(d, r => toString(EvLambda(r)))
+  | EvDistribution(dist) => GenericDist.toString(dist)
  | EvLambda(lambdaValue) => `lambda(${Js.Array2.toString(lambdaValue.parameters)}=>internal code)`
+  | EvModule(m) => `@${m->toStringRecord}`
  | EvNumber(aNumber) => Js.String.make(aNumber)
+  | EvRecord(aRecord) => aRecord->toStringRecord
  | EvString(aString) => `'${aString}'`
  | EvSymbol(aString) => `:${aString}`
-  | EvRecord(aRecord) => aRecord->toStringRecord
-  | EvDistribution(dist) => GenericDist.toString(dist)
-  | EvDate(date) => DateTime.Date.toString(date)
  | EvTimeDuration(t) => DateTime.Duration.toString(t)
-  | EvDeclaration(d) => Declaration.toString(d, r => toString(EvLambda(r)))
+  | EvType(t) => `type${t->toStringRecord}`
  | EvTypeIdentifier(id) => `#${id}`
-  | EvModule(m) => `@${m->toStringRecord}`
  }
 and toStringRecord = aRecord => {
  let pairs =
@ -88,72 +90,3 @@ type environment = DistributionOperation.env

@genType
 let defaultEnvironment: environment = DistributionOperation.defaultEnv
-
-type expressionValueType =
-  | EvtArray
-  | EvtArrayString
-  | EvtBool
-  | EvtCall
-  | EvtDistribution
-  | EvtLambda
-  | EvtNumber
-  | EvtRecord
-  | EvtString
-  | EvtSymbol
-  | EvtDate
-  | EvtTimeDuration
-  | EvtDeclaration
-  | EvtTypeIdentifier
-  | EvtModule
-
-type functionCallSignature = CallSignature(string, array<expressionValueType>)
-type functionDefinitionSignature =
-  FunctionDefinitionSignature(functionCallSignature, expressionValueType)
-
-let valueToValueType = value =>
-  switch value {
-  | EvArray(_) => EvtArray
-  | EvArrayString(_) => EvtArrayString
-  | EvBool(_) => EvtBool
-  | EvCall(_) => EvtCall
-  | EvDistribution(_) => EvtDistribution
-  | EvLambda(_) => EvtLambda
-  | EvNumber(_) => EvtNumber
-  | EvRecord(_) => EvtRecord
-  | EvString(_) => EvtString
-  | EvSymbol(_) => EvtSymbol
-  | EvDate(_) => EvtDate
-  | EvTimeDuration(_) => EvtTimeDuration
-  | EvDeclaration(_) => EvtDeclaration
-  | EvTypeIdentifier(_) => EvtTypeIdentifier
-  | EvModule(_) => EvtModule
-  }
-
-let functionCallToCallSignature = (functionCall: functionCall): functionCallSignature => {
-  let (fn, args) = functionCall
-  CallSignature(fn, args->Js.Array2.map(valueToValueType))
-}
-
-let valueTypeToString = (valueType: expressionValueType): string =>
-  switch valueType {
-  | EvtArray => `Array`
-  | EvtArrayString => `ArrayString`
-  | EvtBool => `Bool`
-  | EvtCall => `Call`
-  | EvtDistribution => `Distribution`
-  | EvtLambda => `Lambda`
-  | EvtNumber => `Number`
-  | EvtRecord => `Record`
-  | EvtString => `String`
-  | EvtSymbol => `Symbol`
-  | EvtDate => `Date`
-  | EvtTimeDuration => `Duration`
-  | EvtDeclaration => `Declaration`
-  | EvtTypeIdentifier => `TypeIdentifier`
-  | EvtModule => `Module`
-  }
-
-let functionCallSignatureToString = (functionCallSignature: functionCallSignature): string => {
-  let CallSignature(fn, args) = functionCallSignature
-  `${fn}(${args->Js.Array2.map(valueTypeToString)->Js.Array2.toString})`
-}
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_InternalExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_InternalExpressionValue.res
@ -7,8 +7,8 @@ type environment = ExternalExpressionValue.environment
 let defaultEnvironment = ExternalExpressionValue.defaultEnvironment

 type rec t =
-  | IEvArray(array<t>) // FIXME: Convert
-  | IEvArrayString(array<string>) // FIXME: Convert
+  | IEvArray(array<t>) // FIXME: Convert to MapInt
+  | IEvArrayString(array<string>)
  | IEvBool(bool)
  | IEvCall(string) // External function call
  | IEvDate(Js.Date.t)
@ -21,6 +21,7 @@ type rec t =
  | IEvString(string)
  | IEvSymbol(string)
  | IEvTimeDuration(float)
+  | IEvType(map)
  | IEvTypeIdentifier(string)
 and map = Belt.Map.String.t<t>
 and nameSpace = NameSpace(Belt.Map.String.t<t>)
@ -56,6 +57,7 @@ let rec toString = aValue =>
  | IEvRecord(aMap) => aMap->toStringMap
  | IEvString(aString) => `'${aString}'`
  | IEvSymbol(aString) => `:${aString}`
+  | IEvType(aMap) => aMap->toStringMap
  | IEvTimeDuration(t) => DateTime.Duration.toString(t)
  | IEvTypeIdentifier(id) => `#${id}`
  }
@ -78,17 +80,18 @@ let toStringWithType = aValue =>
  | IEvArrayString(_) => `ArrayString::${toString(aValue)}`
  | IEvBool(_) => `Bool::${toString(aValue)}`
  | IEvCall(_) => `Call::${toString(aValue)}`
+  | IEvDate(_) => `Date::${toString(aValue)}`
+  | IEvDeclaration(_) => `Declaration::${toString(aValue)}`
  | IEvDistribution(_) => `Distribution::${toString(aValue)}`
  | IEvLambda(_) => `Lambda::${toString(aValue)}`
+  | IEvModule(_) => `Module::${toString(aValue)}`
  | IEvNumber(_) => `Number::${toString(aValue)}`
  | IEvRecord(_) => `Record::${toString(aValue)}`
  | IEvString(_) => `String::${toString(aValue)}`
  | IEvSymbol(_) => `Symbol::${toString(aValue)}`
-  | IEvDate(_) => `Date::${toString(aValue)}`
  | IEvTimeDuration(_) => `Date::${toString(aValue)}`
-  | IEvDeclaration(_) => `Declaration::${toString(aValue)}`
+  | IEvType(_) => `Type::${toString(aValue)}`
  | IEvTypeIdentifier(_) => `TypeIdentifier::${toString(aValue)}`
-  | IEvModule(_) => `Module::${toString(aValue)}`
  }

 let argsToString = (args: array<t>): string => {
@ -120,17 +123,18 @@ type internalExpressionValueType =
  | EvtArrayString
  | EvtBool
  | EvtCall
+  | EvtDate
+  | EvtDeclaration
  | EvtDistribution
  | EvtLambda
+  | EvtModule
  | EvtNumber
  | EvtRecord
  | EvtString
  | EvtSymbol
-  | EvtDate
  | EvtTimeDuration
-  | EvtDeclaration
+  | EvtType
  | EvtTypeIdentifier
-  | EvtModule

 type functionCallSignature = CallSignature(string, array<internalExpressionValueType>)
 type functionDefinitionSignature =
@ -142,17 +146,18 @@ let valueToValueType = value =>
  | IEvArrayString(_) => EvtArrayString
  | IEvBool(_) => EvtBool
  | IEvCall(_) => EvtCall
+  | IEvDate(_) => EvtDate
+  | IEvDeclaration(_) => EvtDeclaration
  | IEvDistribution(_) => EvtDistribution
  | IEvLambda(_) => EvtLambda
+  | IEvModule(_) => EvtModule
  | IEvNumber(_) => EvtNumber
  | IEvRecord(_) => EvtRecord
  | IEvString(_) => EvtString
  | IEvSymbol(_) => EvtSymbol
-  | IEvDate(_) => EvtDate
  | IEvTimeDuration(_) => EvtTimeDuration
-  | IEvDeclaration(_) => EvtDeclaration
+  | IEvType(_) => EvtType
  | IEvTypeIdentifier(_) => EvtTypeIdentifier
-  | IEvModule(_) => EvtModule
  }

 let functionCallToCallSignature = (functionCall: functionCall): functionCallSignature => {
@ -166,17 +171,18 @@ let valueTypeToString = (valueType: internalExpressionValueType): string =>
  | EvtArrayString => `ArrayString`
  | EvtBool => `Bool`
  | EvtCall => `Call`
+  | EvtDate => `Date`
+  | EvtDeclaration => `Declaration`
  | EvtDistribution => `Distribution`
  | EvtLambda => `Lambda`
+  | EvtModule => `Module`
  | EvtNumber => `Number`
  | EvtRecord => `Record`
  | EvtString => `String`
  | EvtSymbol => `Symbol`
-  | EvtDate => `Date`
  | EvtTimeDuration => `Duration`
-  | EvtDeclaration => `Declaration`
+  | EvtType => `Type`
  | EvtTypeIdentifier => `TypeIdentifier`
-  | EvtModule => `Module`
  }

 let functionCallSignatureToString = (functionCallSignature: functionCallSignature): string => {
@ -190,6 +196,11 @@ let rec toExternal = (iev: t): ExternalExpressionValue.t => {
  | IEvArrayString(v) => EvArrayString(v)
  | IEvBool(v) => EvBool(v)
  | IEvCall(v) => EvCall(v)
+  | IEvDeclaration(v) => {
+      let fn = lambdaValueToExternal(v.fn)
+      let args = v.args
+      EvDeclaration({fn: fn, args: args})
+    }
  | IEvDistribution(v) => EvDistribution(v)
  | IEvLambda(v) => EvLambda(lambdaValueToExternal(v))
  | IEvNumber(v) => EvNumber(v)
@ -198,11 +209,7 @@ let rec toExternal = (iev: t): ExternalExpressionValue.t => {
  | IEvSymbol(v) => EvSymbol(v)
  | IEvDate(v) => EvDate(v)
  | IEvTimeDuration(v) => EvTimeDuration(v)
-  | IEvDeclaration(v) => {
-      let fn = lambdaValueToExternal(v.fn)
-      let args = v.args
-      EvDeclaration({fn: fn, args: args})
-    }
+  | IEvType(v) => v->mapToExternal->EvType
  | IEvTypeIdentifier(v) => EvTypeIdentifier(v)
  | IEvModule(v) => v->nameSpaceToTypeScriptBindings->EvModule
  }
@ -228,21 +235,22 @@ let rec toInternal = (ev: ExternalExpressionValue.t): t => {
  | EvArrayString(v) => IEvArrayString(v)
  | EvBool(v) => IEvBool(v)
  | EvCall(v) => IEvCall(v)
-  | EvDistribution(v) => IEvDistribution(v)
-  | EvLambda(v) => IEvLambda(lambdaValueToInternal(v))
-  | EvNumber(v) => IEvNumber(v)
-  | EvRecord(v) => v->recordToInternal->IEvRecord
-  | EvString(v) => IEvString(v)
-  | EvSymbol(v) => IEvSymbol(v)
  | EvDate(v) => IEvDate(v)
-  | EvTimeDuration(v) => IEvTimeDuration(v)
  | EvDeclaration(v) => {
      let fn = lambdaValueToInternal(v.fn)
      let args = v.args
      IEvDeclaration({fn: fn, args: args})
    }
-  | EvTypeIdentifier(v) => IEvTypeIdentifier(v)
+  | EvDistribution(v) => IEvDistribution(v)
+  | EvLambda(v) => IEvLambda(lambdaValueToInternal(v))
  | EvModule(v) => v->nameSpaceFromTypeScriptBindings->IEvModule
+  | EvNumber(v) => IEvNumber(v)
+  | EvRecord(v) => v->recordToInternal->IEvRecord
+  | EvString(v) => IEvString(v)
+  | EvSymbol(v) => IEvSymbol(v)
+  | EvTimeDuration(v) => IEvTimeDuration(v)
+  | EvType(v) => v->recordToInternal->IEvType
+  | EvTypeIdentifier(v) => IEvTypeIdentifier(v)
  }
 }
 and recordToInternal = v =>
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_StdLib.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_StdLib.res
@ -1,4 +1,4 @@
-module Module = Reducer_Category_Module
+module Module = Reducer_Module

 let internalStdLib = Module.emptyModule->SquiggleLibrary_Math.makeBindings

--- a/packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_Math.res
+++ b/packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_Math.res
@ -1,5 +1,5 @@
-module Bindings = Reducer_Category_Module
-module Module = Reducer_Category_Module
+module Bindings = Reducer_Module
+module Module = Reducer_Module

 let availableNumbers: array<(string, float)> = [
  ("pi", Js.Math._PI),
--- a/packages/vscode-ext/package.json
+++ b/packages/vscode-ext/package.json
@ -138,10 +138,10 @@
  "devDependencies": {
    "@types/glob": "^7.2.0",
    "@types/node": "18.x",
-    "@types/vscode": "^1.68.0",
-    "@typescript-eslint/eslint-plugin": "^5.27.0",
-    "@typescript-eslint/parser": "^5.27.0",
-    "eslint": "^8.18.0",
+    "@types/vscode": "^1.69.0",
+    "@typescript-eslint/eslint-plugin": "^5.30.6",
+    "@typescript-eslint/parser": "^5.30.6",
+    "eslint": "^8.19.0",
    "glob": "^8.0.3",
    "js-yaml": "^4.1.0",
    "typescript": "^4.7.4",
@ -149,7 +149,7 @@
  },
  "dependencies": {
    "vscode-languageclient": "^8.0.1",
-    "vscode-languageserver": "^7.0.0",
+    "vscode-languageserver": "^8.0.1",
    "vscode-languageserver-textdocument": "^1.0.5",
    "@quri/squiggle-lang": "^0.2.11"
  }
--- a/packages/website/docs/Api/DistGeneric.mdx
+++ b/packages/website/docs/Api/DistGeneric.mdx
@ -70,12 +70,14 @@ uniform(10, 12);

 ```
 beta: (distribution|number, distribution|number) => distribution
+beta: (dict<{mean: distribution|number, stdev: distribution|number}>) => distribution
 ```

 **Examples**

 ```javascript
 beta(20, 25);
+beta({ mean: 0.39, stdev: 0.1 });
 ```

 ### cauchy
--- a/packages/website/docs/Discussions/Bugs.mdx
+++ b/packages/website/docs/Discussions/Bugs.mdx
@ -16,7 +16,7 @@ If you take the pointwise mixture of two distributions with very different means
 In the following case, the mean of the mixture should be equal to the sum of the means of the parts. These are shown as the first two displayed variables. These variables diverge as the underlying distributions change.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = {value: normal(1,1), weight: 1}
+  defaultCode={`dist1 = {value: normal(1,1), weight: 1}
 dist2 = {value: normal(100000000000,1), weight: 1}
 totalWeight = dist1.weight + dist2.weight
 distMixture = mixture(dist1.value, dist2.value, [dist1.weight, dist2.weight])
@ -30,7 +30,7 @@ separateMeansCombined = (mean(dist1.value) * (dist1.weight) +  mean(dist2.value)
 The means of sample set distributions can vary dramatically, especially as the numbers get high.

 <SquiggleEditor
-  initialSquiggleString={`symbolicDist = 5 to 50333333
+  defaultCode={`symbolicDist = 5 to 50333333
 sampleSetDist = toSampleSet(symbolicDist)
 [mean(symbolicDist), mean(sampleSetDist), symbolicDist, sampleSetDist]`}
 />
--- a/packages/website/docs/Guides/DistributionCreation.mdx
+++ b/packages/website/docs/Guides/DistributionCreation.mdx
@ -22,22 +22,22 @@ If both values are above zero, a `lognormal` distribution is used. If not, a `no
    When <code>5 to 10</code> is entered, both numbers are positive, so it
    generates a lognormal distribution with 5th and 95th percentiles at 5 and
    10.
-    <SquiggleEditor initialSquiggleString="5 to 10" />
+    <SquiggleEditor defaultCode="5 to 10" />
  </TabItem>
  <TabItem value="ex3" label="to(5,10)">
    <code>5 to 10</code> does the same thing as <code>to(5,10)</code>.
-    <SquiggleEditor initialSquiggleString="to(5,10)" />
+    <SquiggleEditor defaultCode="to(5,10)" />
  </TabItem>
  <TabItem value="ex2" label="-5 to 5">
    When <code>-5 to 5</code> is entered, there's negative values, so it
    generates a normal distribution. This has 5th and 95th percentiles at 5 and
    10.
-    <SquiggleEditor initialSquiggleString="-5 to -3" />
+    <SquiggleEditor defaultCode="-5 to -3" />
  </TabItem>
  <TabItem value="ex4" label="1 to 10000">
    It's very easy to generate distributions with very long tails. If this
    happens, you can click the "log x scale" box to view this using a log scale.
-    <SquiggleEditor initialSquiggleString="1 to 10000" />
+    <SquiggleEditor defaultCode="1 to 10000" />
  </TabItem>
 </Tabs>

@ -76,16 +76,16 @@ The `mixture` mixes combines multiple distributions to create a mixture. You can

 <Tabs>
  <TabItem value="ex1" label="Simple" default>
-    <SquiggleEditor initialSquiggleString="mixture(1 to 2, 5 to 8, 9 to 10)" />
+    <SquiggleEditor defaultCode="mixture(1 to 2, 5 to 8, 9 to 10)" />
  </TabItem>
  <TabItem value="ex2" label="With Weights">
-    <SquiggleEditor initialSquiggleString="mixture(1 to 2, 5 to 8, 9 to 10, [0.1, 0.1, 0.8])" />
+    <SquiggleEditor defaultCode="mixture(1 to 2, 5 to 8, 9 to 10, [0.1, 0.1, 0.8])" />
  </TabItem>
  <TabItem value="ex3" label="With Continuous and Discrete Inputs">
-    <SquiggleEditor initialSquiggleString="mixture(1 to 5, 8 to 10, 1, 3, 20)" />
+    <SquiggleEditor defaultCode="mixture(1 to 5, 8 to 10, 1, 3, 20)" />
  </TabItem>
  <TabItem value="ex4" label="Array of Distributions Input">
-    <SquiggleEditor initialSquiggleString="mx([1 to 2, exponential(1)], [1,1])" />
+    <SquiggleEditor defaultCode="mx([1 to 2, exponential(1)], [1,1])" />
  </TabItem>
 </Tabs>

@ -111,7 +111,7 @@ The `mixture` mixes combines multiple distributions to create a mixture. You can
    In this case, I have a 20% chance of spending 0 time with it. I might estimate my hours with,
  </p>
  <SquiggleEditor
-    initialSquiggleString={`hours_the_project_will_take = 5 to 20
+    defaultCode={`hours_the_project_will_take = 5 to 20
 chance_of_doing_anything = 0.8
 mx(hours_the_project_will_take, 0, [chance_of_doing_anything, 1 - chance_of_doing_anything])`}
  />
@ -125,7 +125,7 @@ mx(hours_the_project_will_take, 0, [chance_of_doing_anything, 1 - chance_of_doin
  very wide, just in case they were dramatically off for some weird reason.
  </p>
 <SquiggleEditor
-  initialSquiggleString={`forecast = 3 to 30
+  defaultCode={`forecast = 3 to 30
 chance_completely_wrong = 0.05
 forecast_if_completely_wrong = -100 to 200
 mx(forecast, forecast_if_completely_wrong, [1-chance_completely_wrong, chance_completely_wrong])`}
@ -141,10 +141,10 @@ Creates a [normal distribution](https://en.wikipedia.org/wiki/Normal_distributio

 <Tabs>
  <TabItem value="ex1" label="normal(5,1)" default>
-    <SquiggleEditor initialSquiggleString="normal(5, 1)" />
+    <SquiggleEditor defaultCode="normal(5, 1)" />
  </TabItem>
  <TabItem value="ex2" label="normal(100000000000, 100000000000)">
-    <SquiggleEditor initialSquiggleString="normal(100000000000, 100000000000)" />
+    <SquiggleEditor defaultCode="normal(100000000000, 100000000000)" />
  </TabItem>
 </Tabs>

@ -165,7 +165,7 @@ Creates a [log-normal distribution](https://en.wikipedia.org/wiki/Log-normal_dis
 you take the log of our lognormal distribution. They can be difficult to directly reason about.
 Because of this complexity, we recommend typically using the <a href="#to">to</a> syntax instead of estimating `mu` and `sigma` directly.

-<SquiggleEditor initialSquiggleString="lognormal(0, 0.7)" />
+<SquiggleEditor defaultCode="lognormal(0, 0.7)" />

 ### Arguments

@ -185,7 +185,7 @@ Because of this complexity, we recommend typically using the <a href="#to">to</a
    are identical:
  </p>
  <SquiggleEditor
-    initialSquiggleString={`normalMean = 10
+    defaultCode={`normalMean = 10
 normalStdDev = 2
 logOfLognormal = log(lognormal(normalMean, normalStdDev))
 [logOfLognormal, normal(normalMean, normalStdDev)]`}
@ -198,7 +198,7 @@ logOfLognormal = log(lognormal(normalMean, normalStdDev))

 Creates a [uniform distribution](<https://en.wikipedia.org/wiki/Uniform_distribution_(continuous)>) with the given low and high values.

-<SquiggleEditor initialSquiggleString="uniform(3,7)" />
+<SquiggleEditor defaultCode="uniform(3,7)" />

 ### Arguments

@ -236,19 +236,19 @@ with values at 1 and 2. Therefore, this is the same as `mixture(pointMass(1),poi

 <Tabs>
  <TabItem value="ex1" label="pointMass(3)" default>
-    <SquiggleEditor initialSquiggleString="pointMass(3)" />
+    <SquiggleEditor defaultCode="pointMass(3)" />
  </TabItem>
  <TabItem value="ex3" label="mixture(1,3,5)">
-    <SquiggleEditor initialSquiggleString="mixture(1,3,5)" />
+    <SquiggleEditor defaultCode="mixture(1,3,5)" />
  </TabItem>
  <TabItem value="ex2" label="normal(5,2) * 6">
-    <SquiggleEditor initialSquiggleString="normal(5,2) * 6" />
+    <SquiggleEditor defaultCode="normal(5,2) * 6" />
  </TabItem>
  <TabItem value="ex4" label="dotAdd(normal(5,2), 6)">
-    <SquiggleEditor initialSquiggleString="dotAdd(normal(5,2), 6)" />
+    <SquiggleEditor defaultCode="dotAdd(normal(5,2), 6)" />
  </TabItem>
  <TabItem value="ex5" label="dotMultiply(normal(5,2), 6)">
-    <SquiggleEditor initialSquiggleString="dotMultiply(normal(5,2), 6)" />
+    <SquiggleEditor defaultCode="dotMultiply(normal(5,2), 6)" />
  </TabItem>
 </Tabs>

@ -259,24 +259,31 @@ with values at 1 and 2. Therefore, this is the same as `mixture(pointMass(1),poi
 ## Beta

 `beta(alpha:number, beta:number)`
+`beta({mean: number, stdev: number})`

 Creates a [beta distribution](https://en.wikipedia.org/wiki/Beta_distribution) with the given `alpha` and `beta` values. For a good summary of the beta distribution, see [this explanation](https://stats.stackexchange.com/a/47782) on Stack Overflow.

 <Tabs>
  <TabItem value="ex1" label="beta(10, 20)" default>
-    <SquiggleEditor initialSquiggleString="beta(10,20)" />
+    <SquiggleEditor defaultCode="beta(10,20)" />
  </TabItem>
  <TabItem value="ex2" label="beta(1000, 1000)">
-    <SquiggleEditor initialSquiggleString="beta(1000, 2000)" />
+    <SquiggleEditor defaultCode="beta(1000, 2000)" />
  </TabItem>
  <TabItem value="ex3" label="beta(1, 10)">
-    <SquiggleEditor initialSquiggleString="beta(1, 10)" />
+    <SquiggleEditor defaultCode="beta(1, 10)" />
  </TabItem>
  <TabItem value="ex4" label="beta(10, 1)">
-    <SquiggleEditor initialSquiggleString="beta(10, 1)" />
+    <SquiggleEditor defaultCode="beta(10, 1)" />
  </TabItem>
  <TabItem value="ex5" label="beta(0.8, 0.8)">
-    <SquiggleEditor initialSquiggleString="beta(0.8, 0.8)" />
+    <SquiggleEditor defaultCode="beta(0.8, 0.8)" />
+  </TabItem>
+  <TabItem
+    value="from mean and standard deviation"
+    label="beta({mean: 0.39, stdev: 0.1})"
+  >
+    <SquiggleEditor initialSquiggleString="beta({mean: 0.39, stdev: 0.1})" />
  </TabItem>
 </Tabs>

@ -295,16 +302,16 @@ Creates a [beta distribution](https://en.wikipedia.org/wiki/Beta_distribution) w
    <summary>Examples</summary>
    <Tabs>
      <TabItem value="ex1" label="beta(0.3, 0.3)" default>
-        <SquiggleEditor initialSquiggleString="beta(0.3, 0.3)" />
+        <SquiggleEditor defaultCode="beta(0.3, 0.3)" />
      </TabItem>
      <TabItem value="ex2" label="beta(0.5, 0.5)">
-        <SquiggleEditor initialSquiggleString="beta(0.5, 0.5)" />
+        <SquiggleEditor defaultCode="beta(0.5, 0.5)" />
      </TabItem>
      <TabItem value="ex3" label="beta(0.8, 0.8)">
-        <SquiggleEditor initialSquiggleString="beta(.8,.8)" />
+        <SquiggleEditor defaultCode="beta(.8,.8)" />
      </TabItem>
      <TabItem value="ex4" label="beta(0.9, 0.9)">
-        <SquiggleEditor initialSquiggleString="beta(.9,.9)" />
+        <SquiggleEditor defaultCode="beta(.9,.9)" />
      </TabItem>
    </Tabs>
  </details>
@ -316,7 +323,7 @@ Creates a [beta distribution](https://en.wikipedia.org/wiki/Beta_distribution) w

 Creates an [exponential distribution](https://en.wikipedia.org/wiki/Exponential_distribution) with the given rate.

-<SquiggleEditor initialSquiggleString="exponential(4)" />
+<SquiggleEditor defaultCode="exponential(4)" />

 ### Arguments

@ -334,7 +341,7 @@ Creates a [triangular distribution](https://en.wikipedia.org/wiki/Triangular_dis
 - `mode`: Number greater than `low`
 - `high`: Number greater than `mode`

-<SquiggleEditor initialSquiggleString="triangular(1, 2, 4)" />
+<SquiggleEditor defaultCode="triangular(1, 2, 4)" />

 ## FromSamples

@ -342,7 +349,7 @@ Creates a [triangular distribution](https://en.wikipedia.org/wiki/Triangular_dis

 Creates a sample set distribution using an array of samples.

-<SquiggleEditor initialSquiggleString="fromSamples([1,2,3,4,6,5,5,5])" />
+<SquiggleEditor defaultCode="fromSamples([1,2,3,4,6,5,5,5])" />

 ### Arguments

--- a/packages/website/docs/Guides/Functions.mdx
+++ b/packages/website/docs/Guides/Functions.mdx
@ -16,7 +16,7 @@ the value of one random sample chosen from the first distribution and the value
 chosen from the second distribution.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 + dist2`}
 />
@ -28,7 +28,7 @@ the distribution of the value of one random sample chosen from the first distrib
 the value of one random sample chosen from the second distribution.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 - dist2`}
 />
@ -40,14 +40,14 @@ the value of one random sample chosen from the first distribution times the valu
 chosen from the second distribution.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 * dist2`}
 />

 We also provide concatenation of two distributions as a syntax sugar for `*`

-<SquiggleEditor initialSquiggleString="(0.1 to 1) triangular(1,2,3)" />
+<SquiggleEditor defaultCode="(0.1 to 1) triangular(1,2,3)" />

 ### Division

@ -58,7 +58,7 @@ chosen from the second distribution. If the second distribution has some values
 tends to be particularly unstable.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 / dist2`}
 />
@ -69,12 +69,12 @@ A projection over a contracted x-axis. The exponentiation operation represents t
 the exponentiation of the value of one random sample chosen from the first distribution to the power of
 the value one random sample chosen from the second distribution.

-<SquiggleEditor initialSquiggleString={`(0.1 to 1) ^ beta(2, 3)`} />
+<SquiggleEditor defaultCode={`(0.1 to 1) ^ beta(2, 3)`} />

 ### Taking the base `e` exponential

 <SquiggleEditor
-  initialSquiggleString={`dist = triangular(1,2,3)
+  defaultCode={`dist = triangular(1,2,3)
 exp(dist)`}
 />

@ -83,19 +83,19 @@ exp(dist)`}
 A projection over a stretched x-axis.

 <SquiggleEditor
-  initialSquiggleString={`dist = triangular(1,2,3)
+  defaultCode={`dist = triangular(1,2,3)
 log(dist)`}
 />

 <SquiggleEditor
-  initialSquiggleString={`dist = beta(1,2)
+  defaultCode={`dist = beta(1,2)
 log10(dist)`}
 />

 Base `x`

 <SquiggleEditor
-  initialSquiggleString={`x = 2
+  defaultCode={`x = 2
 dist = beta(2,3)
 log(dist, x)`}
 />
@ -114,7 +114,7 @@ For every point on the x-axis, operate the corresponding points in the y axis of
 TODO: this isn't in the new interpreter/parser yet.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 .+ dist2`}
 />
@ -124,7 +124,7 @@ dist1 .+ dist2`}
 TODO: this isn't in the new interpreter/parser yet.

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 .- dist2`}
 />
@ -132,7 +132,7 @@ dist1 .- dist2`}
 ### Pointwise multiplication

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 .* dist2`}
 />
@ -140,7 +140,7 @@ dist1 .* dist2`}
 ### Pointwise division

 <SquiggleEditor
-  initialSquiggleString={`dist1 = uniform(0,20)
+  defaultCode={`dist1 = uniform(0,20)
 dist2 = normal(10,8)
 dist1 ./ dist2`}
 />
@ -148,7 +148,7 @@ dist1 ./ dist2`}
 ### Pointwise exponentiation

 <SquiggleEditor
-  initialSquiggleString={`dist1 = 1 to 10
+  defaultCode={`dist1 = 1 to 10
 dist2 = triangular(1,2,3)
 dist1 .^ dist2`}
 />
@ -160,7 +160,7 @@ dist1 .^ dist2`}
 The `pdf(dist, x)` function returns the density of a distribution at the
 given point x.

-<SquiggleEditor initialSquiggleString="pdf(normal(0,1),0)" />
+<SquiggleEditor defaultCode="pdf(normal(0,1),0)" />

 #### Validity

@ -172,7 +172,7 @@ given point x.
 The `cdf(dist, x)` gives the cumulative probability of the distribution
 or all values lower than x. It is the inverse of `quantile`.

-<SquiggleEditor initialSquiggleString="cdf(normal(0,1),0)" />
+<SquiggleEditor defaultCode="cdf(normal(0,1),0)" />

 #### Validity

@ -185,7 +185,7 @@ The `quantile(dist, prob)` gives the value x or which the probability for all va
 lower than x is equal to prob. It is the inverse of `cdf`. In the literature, it
 is also known as the quantiles function.

-<SquiggleEditor initialSquiggleString="quantile(normal(0,1),0.5)" />
+<SquiggleEditor defaultCode="quantile(normal(0,1),0.5)" />

 #### Validity

@ -196,29 +196,29 @@ is also known as the quantiles function.

 The `mean(distribution)` function gives the mean (expected value) of a distribution.

-<SquiggleEditor initialSquiggleString="mean(normal(5, 10))" />
+<SquiggleEditor defaultCode="mean(normal(5, 10))" />

 ### Sampling a distribution

 The `sample(distribution)` samples a given distribution.

-<SquiggleEditor initialSquiggleString="sample(normal(0, 10))" />
+<SquiggleEditor defaultCode="sample(normal(0, 10))" />

 ## Converting between distribution formats

 Recall the [three formats of distributions](https://develop--squiggle-documentation.netlify.app/docs/Discussions/Three-Types-Of-Distributions). We can force any distribution into `SampleSet` format

-<SquiggleEditor initialSquiggleString="toSampleSet(normal(5, 10))" />
+<SquiggleEditor defaultCode="toSampleSet(normal(5, 10))" />

 Or `PointSet` format

-<SquiggleEditor initialSquiggleString="toPointSet(normal(5, 10))" />
+<SquiggleEditor defaultCode="toPointSet(normal(5, 10))" />

 ### `toSampleSet` has two signatures

 Above, we saw the unary `toSampleSet`, which uses an internal hardcoded number of samples. If you'd like to provide the number of samples, it has a binary signature as well (floored)

-<SquiggleEditor initialSquiggleString="[toSampleSet(0.1 to 1, 100.1), toSampleSet(0.1 to 1, 5000), toSampleSet(0.1 to 1, 20000)]" />
+<SquiggleEditor defaultCode="[toSampleSet(0.1 to 1, 100.1), toSampleSet(0.1 to 1, 5000), toSampleSet(0.1 to 1, 20000)]" />

 #### Validity

@ -230,13 +230,13 @@ Some distribution operations (like horizontal shift) return an unnormalized dist

 We provide a `normalize` function

-<SquiggleEditor initialSquiggleString="normalize((0.1 to 1) + triangular(0.1, 1, 10))" />
+<SquiggleEditor defaultCode="normalize((0.1 to 1) + triangular(0.1, 1, 10))" />

 #### Validity - Input to `normalize` must be a dist

 We provide a predicate `isNormalized`, for when we have simple control flow

-<SquiggleEditor initialSquiggleString="isNormalized((0.1 to 1) * triangular(0.1, 1, 10))" />
+<SquiggleEditor defaultCode="isNormalized((0.1 to 1) * triangular(0.1, 1, 10))" />

 #### Validity

@ -246,7 +246,7 @@ We provide a predicate `isNormalized`, for when we have simple control flow

 You may like to debug by right clicking your browser and using the _inspect_ functionality on the webpage, and viewing the _console_ tab. Then, wrap your squiggle output with `inspect` to log an internal representation.

-<SquiggleEditor initialSquiggleString="inspect(toSampleSet(0.1 to 1, 100))" />
+<SquiggleEditor defaultCode="inspect(toSampleSet(0.1 to 1, 100))" />

 Save for a logging side effect, `inspect` does nothing to input and returns it.

@ -254,12 +254,12 @@ Save for a logging side effect, `inspect` does nothing to input and returns it.

 You can cut off from the left

-<SquiggleEditor initialSquiggleString="truncateLeft(0.1 to 1, 0.5)" />
+<SquiggleEditor defaultCode="truncateLeft(0.1 to 1, 0.5)" />

 You can cut off from the right

-<SquiggleEditor initialSquiggleString="truncateRight(0.1 to 1, 0.5)" />
+<SquiggleEditor defaultCode="truncateRight(0.1 to 1, 0.5)" />

 You can cut off from both sides

-<SquiggleEditor initialSquiggleString="truncate(0.1 to 1, 0.5, 1.5)" />
+<SquiggleEditor defaultCode="truncate(0.1 to 1, 0.5, 1.5)" />
--- a/packages/website/docs/Guides/Language.mdx
+++ b/packages/website/docs/Guides/Language.mdx
@ -9,22 +9,22 @@ import { SquiggleEditor } from "../../src/components/SquiggleEditor";

 ### Distributions

-<SquiggleEditor initialSquiggleString={`mixture(1 to 2, 3, [0.3, 0.7])`} />
+<SquiggleEditor defaultCode={`mixture(1 to 2, 3, [0.3, 0.7])`} />

 ### Numbers

-<SquiggleEditor initialSquiggleString="4.32" />
+<SquiggleEditor defaultCode="4.32" />

 ### Arrays

 <SquiggleEditor
-  initialSquiggleString={`[beta(1,10), 4, isNormalized(toSampleSet(1 to 2))]`}
+  defaultCode={`[beta(1,10), 4, isNormalized(toSampleSet(1 to 2))]`}
 />

 ### Records

 <SquiggleEditor
-  initialSquiggleString={`d = {dist: triangular(0, 1, 2), weight: 0.25}
+  defaultCode={`d = {dist: triangular(0, 1, 2), weight: 0.25}
 d.dist`}
 />

@ -33,7 +33,7 @@ d.dist`}
 A statement assigns expressions to names. It looks like `<symbol> = <expression>`

 <SquiggleEditor
-  initialSquiggleString={`value_of_work = 10 to 70
+  defaultCode={`value_of_work = 10 to 70
 5 + value_of_work / 75`}
 />

@ -42,7 +42,7 @@ A statement assigns expressions to names. It looks like `<symbol> = <expression>
 We can define functions

 <SquiggleEditor
-  initialSquiggleString={`ozzie_estimate(t) = lognormal(t^(1.1), 0.5)
+  defaultCode={`ozzie_estimate(t) = lognormal(t^(1.1), 0.5)
 nuno_estimate(t, m) = mixture(normal(-5, 1), lognormal(m, t / 1.25))
 ozzie_estimate(1) * nuno_estimate(1, 1)`}
 />
--- a/packages/website/docs/Introduction.md
+++ b/packages/website/docs/Introduction.md
@ -10,7 +10,7 @@ Squiggle is an _estimation language_, and a syntax for _calculating and expressi
 - [Gallery](./Discussions/Gallery)
 - [Squiggle playground](/playground)
 - [Language basics](./Guides/Language)
- [Squiggle functions source of truth](./docs/Guides/Functions)
+- [Squiggle functions source of truth](./Guides/Functions)
 - [Known bugs](./Discussions/Bugs)
 - [Original lesswrong sequence](https://www.lesswrong.com/s/rDe8QE5NvXcZYzgZ3)
 - [Author your squiggle models as Observable notebooks](https://observablehq.com/@hazelfire/squiggle)
--- a/packages/website/package.json
+++ b/packages/website/package.json
@ -12,14 +12,14 @@
    "format": "prettier --write ."
  },
  "dependencies": {
-    "@docusaurus/core": "2.0.0-beta.21",
-    "@docusaurus/preset-classic": "2.0.0-beta.21",
+    "@docusaurus/core": "2.0.0-beta.22",
+    "@docusaurus/preset-classic": "2.0.0-beta.22",
    "@quri/squiggle-components": "^0.2.20",
    "base64-js": "^1.5.1",
-    "clsx": "^1.1.1",
+    "clsx": "^1.2.1",
    "hast-util-is-element": "2.1.2",
    "pako": "^2.0.4",
-    "prism-react-renderer": "^1.3.3",
+    "prism-react-renderer": "^1.3.5",
    "react": "^18.1.0",
    "react-dom": "^18.2.0",
    "rehype-katex": "^5",
--- a/packages/website/src/pages/playground.js
+++ b/packages/website/src/pages/playground.js
@ -36,11 +36,16 @@ function setHashData(data) {
 }

 export default function PlaygroundPage() {
+  const hashData = getHashData();
+  if (hashData.initialSquiggleString) {
+    hashData.defaultCode = String(hashData.initialSquiggleString);
+    delete hashData.initialSquiggleString;
+  }
  const playgroundProps = {
-    initialSquiggleString: "normal(0,1)",
+    defaultCode: "normal(0,1)",
    height: 700,
    showTypes: true,
-    ...getHashData(),
+    ...hashData,
    onCodeChange: (code) => setHashData({ initialSquiggleString: code }),
    onSettingsChange: (settings) => {
      const { showTypes, showControls, showSummary, showEditor } = settings;
--- a/yarn.lock
+++ b/yarn.lock