Merge branch 'develop' into mix-distributions

2022-04-13 11:22:43 +10:00 · 2022-04-13 11:22:43 +10:00 · 38135f0c81
commit 38135f0c81
parent f102d70d80 b17f638483
44 changed files with 788 additions and 462 deletions
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@ -9,21 +9,21 @@
 # This also holds true for GitHub teams.

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

 # Typescript 
 *.tsx @Hazelfire @OAGr
 *.ts @Hazelfire @OAGr

 # Javascript
-*.js @Hazelfire
+*.js @Hazelfire @OAGr

 # Any opsy files
-.github/* @quinn-dougherty
-*.json @quinn-dougherty @Hazelfire
-*.y*ml @quinn-dougherty
-*.config.js @Hazelfire
+.github/** @quinn-dougherty @OAGr
+*.json @quinn-dougherty @Hazelfire @OAGr
+*.y*ml @quinn-dougherty @OAGr
+*.config.js @Hazelfire @OAGr

 # Documentation
 *.md @quinn-dougherty @OAGr @Hazelfire
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@ -25,17 +25,17 @@ jobs:
    steps:
      - id: skip_lang_check
        name: Check if the changes are about squiggle-lang src files
-        uses: fkirc/skip-duplicate-actions@master
+        uses: fkirc/skip-duplicate-actions@v3.4.1
        with:
          paths: '["packages/squiggle-lang/**"]'
      - id: skip_components_check
        name: Check if the changes are about components src files
-        uses: fkirc/skip-duplicate-actions@master
+        uses: fkirc/skip-duplicate-actions@v3.4.1
        with:
          paths: '["packages/components/**"]'
      - id: skip_website_check
        name: Check if the changes are about website src files
-        uses: fkirc/skip-duplicate-actions@master
+        uses: fkirc/skip-duplicate-actions@v3.4.1
        with:
          paths: '["packages/website/**"]'

@ -58,7 +58,7 @@ jobs:
        uses: creyD/prettier_action@v4.2
        with:
          dry: true
-          prettier_options: --check .
+          prettier_options: --check packages/squiggle-lang

  lang-build-test-bundle:
    name: Language build, test, and bundle
@ -97,7 +97,7 @@ jobs:
        uses: creyD/prettier_action@v4.2
        with:
          dry: true
-          prettier_options: --check .
+          prettier_options: --check packages/components

  components-bundle-build:
    name: Components bundle and build
@ -134,7 +134,7 @@ jobs:
        uses: creyD/prettier_action@v4.2
        with:
          dry: true
-          prettier_options: --check .
+          prettier_options: --check packages/website

  website-build:
    name: Website build
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@ -51,4 +51,91 @@ See [here](https://github.com/NixOS/nixpkgs/issues/107375)

 # Pull request protocol

-Please work against `staging` branch. **Do not** work against `master`. Please do not merge without approval from some subset of Quinn, Sam, and Ozzie; they will be auto-pinged.
+Please work against `develop` branch. **Do not** work against `master`.
+
+- For rescript code: Quinn and Ozzie are reviewers
+- For js or typescript code: Sam and Ozzie are reviewers
+- For ops code (i.e. yaml, package.json): Quinn and Sam are reviewers
+
+Autopings are set up: if you are not autopinged, you are welcome to comment, but please do not use the formal review feature, send approvals, rejections, or merges.
+
+# Code Quality
+
+- Aim for at least 8/10\* quality in `/packages/squiggle-lang`, and 7/10 quality in `/packages/components`.
+- If you submit a PR that is under a 7, for some reason, describe the reasoning for this in the PR.
+
+* This quality score is subjective.
+
+# Rescript Style
+
+**Use `->` instead of `|>`**  
+Note: Our codebase used to use `|>`, so there's a lot of that in the system. We'll gradually change it.
+
+**Use `x -> y -> z` instead of `let foo = y(x); let bar = z(foo)`**
+
+**Don't use anonymous functions with over three lines**  
+Bad:
+
+```rescript
+  foo
+  -> E.O.fmap(r => {
+    let a = 34;
+    let b = 35;
+    let c = 48;
+    r + a + b + c
+  }
+```
+
+Good:
+
+```rescript
+  let addingFn = (r => {
+    let a = 34;
+    let b = 35;
+    let c = 48;
+    r + a + b + c
+  }
+  foo -> addingFn
+```
+
+**Write out types for everything, even if there's an interface file**  
+We'll try this for one month (ending May 5, 2022), then revisit.
+
+**Use the Rescript optional default syntax**  
+Rescript is clever about function inputs. There's custom syntax for default and optional arguments. In the cases where this applies, use it.
+
+From https://rescript-lang.org/docs/manual/latest/function:
+
+```rescript
+// radius can be omitted
+let drawCircle = (~color, ~radius=?, ()) => {
+  setColor(color)
+  switch radius {
+  | None => startAt(1, 1)
+  | Some(r_) => startAt(r_, r_)
+  }
+}
+```
+
+**Use named arguments**  
+If a function is called externally (in a different file), and has either:
+
+1. Two arguments of the same type
+2. Three paramaters or more.
+
+**Module naming: Use x_y as module names**  
+For example: `Myname_Myproject_Add.res`. Rescript/Ocaml both require files to have unique names, so long names are needed to keep different parts separate from each other.
+
+See [this page](https://dev.to/yawaramin/a-modular-ocaml-project-structure-1ikd) for more information. (Though note that they use two underscores, and we do one. We might refactor that later.
+
+**Module naming: Don't rename modules**
+We have some of this in the Reducer code, but generally discourage it.
+
+**Use interface files (.resi) for files with very public interfaces**
+
+### Recommended Rescript resources
+
+- https://dev.to/yawaramin/a-modular-ocaml-project-structure-1ikd
+- https://github.com/avohq/reasonml-code-style-guide
+- https://cs.brown.edu/courses/cs017/content/docs/reasonml-style.pdf
+- https://github.com/ostera/reason-design-patterns/
--- a/package.json
+++ b/package.json
@ -2,7 +2,8 @@
  "private": true,
  "name": "squiggle",
  "scripts": {
-    "nodeclean": "rm -r node_modules && rm -r packages/*/node_modules"
+    "nodeclean": "rm -r node_modules && rm -r packages/*/node_modules",
+    "format:all": "prettier --write . && cd packages/squiggle-lang && yarn format"
  },
  "devDependencies": {
    "prettier": "^2.6.2"
--- a/packages/components/package.json
+++ b/packages/components/package.json
@ -75,7 +75,7 @@
    "@storybook/preset-create-react-app": "^4.1.0",
    "@storybook/react": "^6.4.20",
    "@types/styled-components": "^5.1.24",
-    "@types/webpack": "^4.41.32",
+    "@types/webpack": "^5.28.0",
    "react-codejar": "^1.1.2",
    "style-loader": "^3.3.1",
    "ts-loader": "^9.2.8",
--- a/packages/squiggle-lang/tests/Distributions/GenericDist_Fixtures.res
+++ b/packages/squiggle-lang/tests/Distributions/GenericDist_Fixtures.res
@ -6,6 +6,8 @@ let normalDist: GenericDist_Types.genericDist = normalDist5
 let betaDist: GenericDist_Types.genericDist = Symbolic(#Beta({alpha: 2.0, beta: 5.0}))
 let lognormalDist: GenericDist_Types.genericDist = Symbolic(#Lognormal({mu: 0.0, sigma: 1.0}))
 let cauchyDist: GenericDist_Types.genericDist = Symbolic(#Cauchy({local: 1.0, scale: 1.0}))
-let triangularDist: GenericDist_Types.genericDist = Symbolic(#Triangular({low: 1.0, medium: 2.0, high: 3.0}))
+let triangularDist: GenericDist_Types.genericDist = Symbolic(
+  #Triangular({low: 1.0, medium: 2.0, high: 3.0}),
+)
 let exponentialDist: GenericDist_Types.genericDist = Symbolic(#Exponential({rate: 2.0}))
 let uniformDist: GenericDist_Types.genericDist = Symbolic(#Uniform({low: 9.0, high: 10.0}))
--- a/packages/squiggle-lang/tests/Distributions/Mixture_test.res
+++ b/packages/squiggle-lang/tests/Distributions/Mixture_test.res
@ -11,14 +11,20 @@ let mkCauchy = (local, scale) => GenericDist_Types.Symbolic(#Cauchy({local: loca
 let mkLognormal = (mu, sigma) => GenericDist_Types.Symbolic(#Lognormal({mu: mu, sigma: sigma}))

 describe("mixture", () => {
-  testAll("fair mean of two normal distributions", list{(0.0, 1e2), (-1e1, -1e-4), (-1e1, 1e2), (-1e1, 1e1)}, tup => {  // should be property
+  testAll(
+    "fair mean of two normal distributions",
+    list{(0.0, 1e2), (-1e1, -1e-4), (-1e1, 1e2), (-1e1, 1e1)},
+    tup => {
+      // should be property
      let (mean1, mean2) = tup
      let meanValue = {
-        run(Mixture([(mkNormal(mean1, 9e-1), 0.5), (mkNormal(mean2, 9e-1), 0.5)])) 
-        -> outputMap(FromDist(ToFloat(#Mean)))
+        run(Mixture([(mkNormal(mean1, 9e-1), 0.5), (mkNormal(mean2, 9e-1), 0.5)]))->outputMap(
+          FromDist(ToFloat(#Mean)),
+        )
      }
      meanValue->unpackFloat->expect->toBeSoCloseTo((mean1 +. mean2) /. 2.0, ~digits=-1)
-  })
+    },
+  )
  testAll(
    "weighted mean of a beta and an exponential",
    // This would not survive property testing, it was easy for me to find cases that NaN'd out.
@ -28,23 +34,17 @@ describe("mixture", () => {
      let betaWeight = 0.25
      let exponentialWeight = 0.75
      let meanValue = {
-          run(Mixture(
-              [
-                (mkBeta(alpha, beta), betaWeight), 
-                (mkExponential(rate), exponentialWeight)
-              ]
-          )) -> outputMap(FromDist(ToFloat(#Mean)))
+        run(
+          Mixture([(mkBeta(alpha, beta), betaWeight), (mkExponential(rate), exponentialWeight)]),
+        )->outputMap(FromDist(ToFloat(#Mean)))
      }
      let betaMean = 1.0 /. (1.0 +. beta /. alpha)
      let exponentialMean = 1.0 /. rate
      meanValue
      ->unpackFloat
      ->expect
-        -> toBeSoCloseTo(
-            betaWeight *. betaMean +. exponentialWeight *. exponentialMean, 
-            ~digits=-1
-        )
-      }
+      ->toBeSoCloseTo(betaWeight *. betaMean +. exponentialWeight *. exponentialMean, ~digits=-1)
+    },
  )
  testAll(
    "weighted mean of lognormal and uniform",
@ -55,8 +55,12 @@ describe("mixture", () => {
      let uniformWeight = 0.6
      let lognormalWeight = 0.4
      let meanValue = {
-              run(Mixture([(mkUniform(low, high), uniformWeight), (mkLognormal(mu, sigma), lognormalWeight)]))
-              -> outputMap(FromDist(ToFloat(#Mean)))
+        run(
+          Mixture([
+            (mkUniform(low, high), uniformWeight),
+            (mkLognormal(mu, sigma), lognormalWeight),
+          ]),
+        )->outputMap(FromDist(ToFloat(#Mean)))
      }
      let uniformMean = (low +. high) /. 2.0
      let lognormalMean = mu +. sigma ** 2.0 /. 2.0
@ -64,7 +68,6 @@ describe("mixture", () => {
      ->unpackFloat
      ->expect
      ->toBeSoCloseTo(uniformWeight *. uniformMean +. lognormalWeight *. lognormalMean, ~digits=-1)
-      }
+    },
  )
 })
-
--- a/packages/squiggle-lang/tests/Distributions/SampleSetDist_test.res
+++ b/packages/squiggle-lang/tests/Distributions/SampleSetDist_test.res
@ -38,4 +38,3 @@ describe("Continuous and discrete splits", () => {
  let toArr2 = discrete2 |> E.FloatFloatMap.toArray
  makeTest("splitMedium at count=500", toArr2 |> Belt.Array.length, 500)
 })
-
--- a/packages/squiggle-lang/tests/Distributions/Symbolic_test.res
+++ b/packages/squiggle-lang/tests/Distributions/Symbolic_test.res
@ -9,121 +9,105 @@ describe("(Symbolic) normalize", () => {
  testAll("has no impact on normal distributions", list{-1e8, -1e-2, 0.0, 1e-4, 1e16}, mean => {
    let normalValue = mkNormal(mean, 2.0)
    let normalizedValue = run(FromDist(ToDist(Normalize), normalValue))
-    normalizedValue 
-    -> unpackDist
-    -> expect
-    -> toEqual(normalValue)
+    normalizedValue->unpackDist->expect->toEqual(normalValue)
  })
 })

 describe("(Symbolic) mean", () => {
  testAll("of normal distributions", list{-1e8, -16.0, -1e-2, 0.0, 1e-4, 32.0, 1e16}, mean => {
-    run(FromDist(ToFloat(#Mean), mkNormal(mean, 4.0))) 
-    -> unpackFloat 
-    -> expect 
-    -> toBeCloseTo(mean)
+    run(FromDist(ToFloat(#Mean), mkNormal(mean, 4.0)))->unpackFloat->expect->toBeCloseTo(mean)
  })

  Skip.test("of normal(0, -1) (it NaNs out)", () => {
-    run(FromDist(ToFloat(#Mean), mkNormal(1e1, -1e0)))
-    -> unpackFloat
-    -> expect
-    -> ExpectJs.toBeFalsy
+    run(FromDist(ToFloat(#Mean), mkNormal(1e1, -1e0)))->unpackFloat->expect->ExpectJs.toBeFalsy
  })

  test("of normal(0, 1e-8) (it doesn't freak out at tiny stdev)", () => {
-    run(FromDist(ToFloat(#Mean), mkNormal(0.0, 1e-8)))
-    -> unpackFloat
-    -> expect
-    -> toBeCloseTo(0.0)
+    run(FromDist(ToFloat(#Mean), mkNormal(0.0, 1e-8)))->unpackFloat->expect->toBeCloseTo(0.0)
  })

  testAll("of exponential distributions", list{1e-7, 2.0, 10.0, 100.0}, rate => {
-    let meanValue = run(FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Exponential({rate: rate}))))
+    let meanValue = run(
+      FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Exponential({rate: rate}))),
+    )
    meanValue->unpackFloat->expect->toBeCloseTo(1.0 /. rate) // https://en.wikipedia.org/wiki/Exponential_distribution#Mean,_variance,_moments,_and_median
  })

  test("of a cauchy distribution", () => {
-    let meanValue = run(FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Cauchy({local: 1.0, scale: 1.0}))))
-    meanValue
-    -> unpackFloat
-    -> expect
-    -> toBeCloseTo(2.01868297874546)
+    let meanValue = run(
+      FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Cauchy({local: 1.0, scale: 1.0}))),
+    )
+    meanValue->unpackFloat->expect->toBeCloseTo(2.01868297874546)
    //-> toBe(GenDistError(Other("Cauchy distributions may have no mean value.")))
  })

-  testAll("of triangular distributions", list{(1.0,2.0,3.0), (-1e7,-1e-7,1e-7), (-1e-7,1e0,1e7), (-1e-16,0.0,1e-16)}, tup => {
+  testAll(
+    "of triangular distributions",
+    list{(1.0, 2.0, 3.0), (-1e7, -1e-7, 1e-7), (-1e-7, 1e0, 1e7), (-1e-16, 0.0, 1e-16)},
+    tup => {
      let (low, medium, high) = tup
-    let meanValue = run(FromDist(
+      let meanValue = run(
+        FromDist(
          ToFloat(#Mean),
-      GenericDist_Types.Symbolic(#Triangular({low: low, medium: medium, high: high}))
-    ))
-    meanValue 
-    -> unpackFloat 
-    -> expect 
-    -> toBeCloseTo((low +. medium +. high) /. 3.0)  // https://www.statology.org/triangular-distribution/
-  })
+          GenericDist_Types.Symbolic(#Triangular({low: low, medium: medium, high: high})),
+        ),
+      )
+      meanValue->unpackFloat->expect->toBeCloseTo((low +. medium +. high) /. 3.0) // https://www.statology.org/triangular-distribution/
+    },
+  )

  // TODO: nonpositive inputs are SUPPOSED to crash.
-  testAll("of beta distributions", list{(1e-4, 6.4e1), (1.28e2, 1e0), (1e-16, 1e-16), (1e16, 1e16), (-1e4, 1e1), (1e1, -1e4)}, tup => {
+  testAll(
+    "of beta distributions",
+    list{(1e-4, 6.4e1), (1.28e2, 1e0), (1e-16, 1e-16), (1e16, 1e16), (-1e4, 1e1), (1e1, -1e4)},
+    tup => {
      let (alpha, beta) = tup
-    let meanValue = run(FromDist(
-      ToFloat(#Mean), 
-      GenericDist_Types.Symbolic(#Beta({alpha: alpha, beta: beta}))
-    ))
-    meanValue 
-    -> unpackFloat 
-    -> expect 
-    -> toBeCloseTo(1.0 /. (1.0 +. (beta /. alpha)))  // https://en.wikipedia.org/wiki/Beta_distribution#Mean
-  })
+      let meanValue = run(
+        FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Beta({alpha: alpha, beta: beta}))),
+      )
+      meanValue->unpackFloat->expect->toBeCloseTo(1.0 /. (1.0 +. beta /. alpha)) // https://en.wikipedia.org/wiki/Beta_distribution#Mean
+    },
+  )

  // TODO: When we have our theory of validators we won't want this to be NaN but to be an error.
  test("of beta(0, 0)", () => {
-    let meanValue = run(FromDist(
-      ToFloat(#Mean), 
-      GenericDist_Types.Symbolic(#Beta({alpha: 0.0, beta: 0.0}))
-    ))
-    meanValue
-    -> unpackFloat
-    -> expect
-    -> ExpectJs.toBeFalsy
+    let meanValue = run(
+      FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Beta({alpha: 0.0, beta: 0.0}))),
+    )
+    meanValue->unpackFloat->expect->ExpectJs.toBeFalsy
  })

-  testAll("of lognormal distributions", list{(2.0, 4.0), (1e-7, 1e-2), (-1e6, 10.0), (1e3, -1e2), (-1e8, -1e4), (1e2, 1e-5)}, tup => { 
+  testAll(
+    "of lognormal distributions",
+    list{(2.0, 4.0), (1e-7, 1e-2), (-1e6, 10.0), (1e3, -1e2), (-1e8, -1e4), (1e2, 1e-5)},
+    tup => {
      let (mu, sigma) = tup
-    let meanValue = run(FromDist(
-      ToFloat(#Mean), 
-      GenericDist_Types.Symbolic(#Lognormal({mu: mu, sigma: sigma}))
-    ))
-    meanValue 
-    -> unpackFloat 
-    -> expect 
-    -> toBeCloseTo(Js.Math.exp(mu +. sigma ** 2.0 /. 2.0 ))  // https://brilliant.org/wiki/log-normal-distribution/
-  })
+      let meanValue = run(
+        FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Lognormal({mu: mu, sigma: sigma}))),
+      )
+      meanValue->unpackFloat->expect->toBeCloseTo(Js.Math.exp(mu +. sigma ** 2.0 /. 2.0)) // https://brilliant.org/wiki/log-normal-distribution/
+    },
+  )

-  testAll("of uniform distributions", list{(1e-5, 12.345), (-1e4, 1e4), (-1e16, -1e2), (5.3e3, 9e9)}, tup => {
+  testAll(
+    "of uniform distributions",
+    list{(1e-5, 12.345), (-1e4, 1e4), (-1e16, -1e2), (5.3e3, 9e9)},
+    tup => {
      let (low, high) = tup
-    let meanValue = run(FromDist(
-      ToFloat(#Mean), 
-      GenericDist_Types.Symbolic(#Uniform({low: low, high: high}))
-    ))
-    meanValue 
-    -> unpackFloat 
-    -> expect 
-    -> toBeCloseTo((low +. high) /. 2.0)  // https://en.wikipedia.org/wiki/Continuous_uniform_distribution#Moments
-  })
+      let meanValue = run(
+        FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Uniform({low: low, high: high}))),
+      )
+      meanValue->unpackFloat->expect->toBeCloseTo((low +. high) /. 2.0) // https://en.wikipedia.org/wiki/Continuous_uniform_distribution#Moments
+    },
+  )

  test("of a float", () => {
-    let meanValue = run(FromDist(
-      ToFloat(#Mean), 
-      GenericDist_Types.Symbolic(#Float(7.7))
-    ))
+    let meanValue = run(FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Float(7.7))))
    meanValue->unpackFloat->expect->toBeCloseTo(7.7)
  })
 })

 describe("Normal distribution with sparklines", () => {
-
  let parameterWiseAdditionPdf = (n1: SymbolicDistTypes.normal, n2: SymbolicDistTypes.normal) => {
    let normalDistAtSumMeanConstr = SymbolicDist.Normal.add(n1, n2)
    let normalDistAtSumMean: SymbolicDistTypes.normal = switch normalDistAtSumMeanConstr {
@ -145,7 +129,8 @@ describe("Normal distribution with sparklines", () => {
  })

  test("parameter-wise addition of two normal distributions", () => {
-    let sparklineMean15 = normalDistAtMean5 -> parameterWiseAdditionPdf(normalDistAtMean10) -> fnImage(range20Float)
+    let sparklineMean15 =
+      normalDistAtMean5->parameterWiseAdditionPdf(normalDistAtMean10)->fnImage(range20Float)
    Sparklines.create(sparklineMean15, ())
    ->expect
    ->toEqual(`▁▁▁▁▁▁▁▁▁▂▃▄▆███▇▅▄▂`)
--- a/packages/squiggle-lang/tests/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res
@ -6,15 +6,17 @@ open Expect
 let expectEvalToBe = (expr: string, answer: string) =>
  Reducer.evaluate(expr)->ExpressionValue.toStringResult->expect->toBe(answer)

+let testEval = (expr, answer) => test(expr, () => expectEvalToBe(expr, answer))
+
 describe("builtin", () => {
  // All MathJs operators and functions are available for string, number and boolean
  // .e.g + - / * > >= < <= == /= not and or
  // See https://mathjs.org/docs/expressions/syntax.html
  // See https://mathjs.org/docs/reference/functions.html
-  test("-1", () => expectEvalToBe("-1", "Ok(-1)"))
-  test("1-1", () => expectEvalToBe("1-1", "Ok(0)"))
-  test("2>1", () => expectEvalToBe("2>1", "Ok(true)"))
-  test("concat('a','b')", () => expectEvalToBe("concat('a','b')", "Ok('ab')"))
+  testEval("-1", "Ok(-1)")
+  testEval("1-1", "Ok(0)")
+  testEval("2>1", "Ok(true)")
+  testEval("concat('a','b')", "Ok('ab')")
 })

 describe("builtin exception", () => {
--- a/packages/squiggle-lang/tests/Reducer/Reducer_MathJs/Reducer_MathJsParse_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_MathJs/Reducer_MathJsParse_test.res
@ -7,45 +7,62 @@ open Expect
 let expectParseToBe = (expr, answer) =>
  Parse.parse(expr)->Result.flatMap(Parse.castNodeType)->Parse.toStringResult->expect->toBe(answer)

+let testParse = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
+
+let testDescriptionParse = (desc, expr, answer) => test(desc, () => expectParseToBe(expr, answer))
+
+module MySkip = {
+  let testParse = (expr, answer) => Skip.test(expr, () => expectParseToBe(expr, answer))
+
+  let testDescriptionParse = (desc, expr, answer) =>
+    Skip.test(desc, () => expectParseToBe(expr, answer))
+}
+
 describe("MathJs parse", () => {
  describe("literals operators paranthesis", () => {
-    test("1", () => expectParseToBe("1", "1"))
-    test("'hello'", () => expectParseToBe("'hello'", "'hello'"))
-    test("true", () => expectParseToBe("true", "true"))
-    test("1+2", () => expectParseToBe("1+2", "add(1, 2)"))
-    test("add(1,2)", () => expectParseToBe("add(1,2)", "add(1, 2)"))
-    test("(1)", () => expectParseToBe("(1)", "(1)"))
-    test("(1+2)", () => expectParseToBe("(1+2)", "(add(1, 2))"))
+    testParse("1", "1")
+    testParse("'hello'", "'hello'")
+    testParse("true", "true")
+    testParse("1+2", "add(1, 2)")
+    testParse("add(1,2)", "add(1, 2)")
+    testParse("(1)", "(1)")
+    testParse("(1+2)", "(add(1, 2))")
+  })
+
+  describe("multi-line", () => {
+    testParse("1; 2", "{1; 2}")
  })

  describe("variables", () => {
-    Skip.test("define", () => expectParseToBe("x = 1", "???"))
-    Skip.test("use", () => expectParseToBe("x", "???"))
+    testParse("x = 1", "x = 1")
+    testParse("x", "x")
+    testParse("x = 1; x", "{x = 1; x}")
  })

  describe("functions", () => {
-    Skip.test("define", () => expectParseToBe("identity(x) = x", "???"))
-    Skip.test("use", () => expectParseToBe("identity(x)", "???"))
+    MySkip.testParse("identity(x) = x", "???")
+    MySkip.testParse("identity(x)", "???")
  })

  describe("arrays", () => {
-    test("empty", () => expectParseToBe("[]", "[]"))
-    test("define", () => expectParseToBe("[0, 1, 2]", "[0, 1, 2]"))
-    test("define with strings", () => expectParseToBe("['hello', 'world']", "['hello', 'world']"))
-    Skip.test("range", () => expectParseToBe("range(0, 4)", "range(0, 4)"))
-    test("index", () => expectParseToBe("([0,1,2])[1]", "([0, 1, 2])[1]"))
+    testDescriptionParse("empty", "[]", "[]")
+    testDescriptionParse("define", "[0, 1, 2]", "[0, 1, 2]")
+    testDescriptionParse("define with strings", "['hello', 'world']", "['hello', 'world']")
+    MySkip.testParse("range(0, 4)", "range(0, 4)")
+    testDescriptionParse("index", "([0,1,2])[1]", "([0, 1, 2])[1]")
  })

  describe("records", () => {
-    test("define", () => expectParseToBe("{a: 1, b: 2}", "{a: 1, b: 2}"))
-    test("use", () => expectParseToBe("record.property", "record['property']"))
+    testDescriptionParse("define", "{a: 1, b: 2}", "{a: 1, b: 2}")
+    testDescriptionParse("use", "record.property", "record['property']")
  })

  describe("comments", () => {
-    Skip.test("define", () => expectParseToBe("# This is a comment", "???"))
+    MySkip.testDescriptionParse("define", "# This is a comment", "???")
  })

  describe("if statement", () => {
-    Skip.test("define", () => expectParseToBe("if (true) { 1 } else { 0 }", "???"))
+    // TODO Tertiary operator instead
+    MySkip.testDescriptionParse("define", "if (true) { 1 } else { 0 }", "???")
  })
 })
--- a/packages/squiggle-lang/tests/Reducer/Reducer_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_test.res
@ -1,6 +1,15 @@
 open Jest
 open Reducer_TestHelpers

+let testParseToBe = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
+
+let testDescriptionParseToBe = (desc, expr, answer) =>
+  test(desc, () => expectParseToBe(expr, answer))
+
+let testEvalToBe = (expr, answer) => test(expr, () => expectEvalToBe(expr, answer))
+
+let testDescriptionEvalToBe = (desc, expr, answer) => test(desc, () => expectEvalToBe(expr, answer))
+
 describe("reducer using mathjs parse", () => {
  // Test the MathJs parser compatibility
  // Those tests toString that there is a semantic mapping from MathJs to Expression
@ -10,31 +19,45 @@ describe("reducer using mathjs parse", () => {
  // Those tests toString that we are converting mathjs parse tree to what we need

  describe("expressions", () => {
-    test("1", () => expectParseToBe("1", "Ok(1)"))
-    test("(1)", () => expectParseToBe("(1)", "Ok(1)"))
-    test("1+2", () => expectParseToBe("1+2", "Ok((:add 1 2))"))
-    test("(1+2)", () => expectParseToBe("1+2", "Ok((:add 1 2))"))
-    test("add(1,2)", () => expectParseToBe("1+2", "Ok((:add 1 2))"))
-    test("1+2*3", () => expectParseToBe("1+2*3", "Ok((:add 1 (:multiply 2 3)))"))
+    testParseToBe("1", "Ok(1)")
+    testParseToBe("(1)", "Ok(1)")
+    testParseToBe("1+2", "Ok((:add 1 2))")
+    testParseToBe("1+2", "Ok((:add 1 2))")
+    testParseToBe("1+2", "Ok((:add 1 2))")
+    testParseToBe("1+2*3", "Ok((:add 1 (:multiply 2 3)))")
  })
  describe("arrays", () => {
    //Note. () is a empty list in Lisp
    //  The only builtin structure in Lisp is list. There are no arrays
    //  [1,2,3] becomes (1 2 3)
-    test("empty", () => expectParseToBe("[]", "Ok(())"))
-    test("[1, 2, 3]", () => expectParseToBe("[1, 2, 3]", "Ok((1 2 3))"))
-    test("['hello', 'world']", () => expectParseToBe("['hello', 'world']", "Ok(('hello' 'world'))"))
-    test("index", () => expectParseToBe("([0,1,2])[1]", "Ok((:$atIndex (0 1 2) (1)))"))
+    testDescriptionParseToBe("empty", "[]", "Ok(())")
+    testParseToBe("[1, 2, 3]", "Ok((1 2 3))")
+    testParseToBe("['hello', 'world']", "Ok(('hello' 'world'))")
+    testDescriptionParseToBe("index", "([0,1,2])[1]", "Ok((:$atIndex (0 1 2) (1)))")
  })
  describe("records", () => {
-    test("define", () =>
-      expectParseToBe("{a: 1, b: 2}", "Ok((:$constructRecord (('a' 1) ('b' 2))))")
-    )
-    test("use", () =>
-      expectParseToBe(
+    testDescriptionParseToBe("define", "{a: 1, b: 2}", "Ok((:$constructRecord (('a' 1) ('b' 2))))")
+    testDescriptionParseToBe(
+      "use",
      "{a: 1, b: 2}.a",
      "Ok((:$atIndex (:$constructRecord (('a' 1) ('b' 2))) ('a')))",
    )
+  })
+  describe("multi-line", () => {
+    testParseToBe("1; 2", "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) 1) 2))")
+    testParseToBe(
+      "1+1; 2+1",
+      "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:add 1 1)) (:add 2 1)))",
+    )
+  })
+  describe("assignment", () => {
+    testParseToBe(
+      "x=1; x",
+      "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :x 1)) :x))",
+    )
+    testParseToBe(
+      "x=1+1; x+1",
+      "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :x (:add 1 1))) (:add :x 1)))",
    )
  })
 })
@ -45,37 +68,51 @@ describe("eval", () => {
  // See https://mathjs.org/docs/expressions/syntax.html
  // See https://mathjs.org/docs/reference/functions.html
  describe("expressions", () => {
-    test("1", () => expectEvalToBe("1", "Ok(1)"))
-    test("1+2", () => expectEvalToBe("1+2", "Ok(3)"))
-    test("(1+2)*3", () => expectEvalToBe("(1+2)*3", "Ok(9)"))
-    test("2>1", () => expectEvalToBe("2>1", "Ok(true)"))
-    test("concat('a ', 'b')", () => expectEvalToBe("concat('a ', 'b')", "Ok('a b')"))
-    test("log(10)", () => expectEvalToBe("log(10)", "Ok(2.302585092994046)"))
-    test("cos(10)", () => expectEvalToBe("cos(10)", "Ok(-0.8390715290764524)"))
+    testEvalToBe("1", "Ok(1)")
+    testEvalToBe("1+2", "Ok(3)")
+    testEvalToBe("(1+2)*3", "Ok(9)")
+    testEvalToBe("2>1", "Ok(true)")
+    testEvalToBe("concat('a ', 'b')", "Ok('a b')")
+    testEvalToBe("log(10)", "Ok(2.302585092994046)")
+    testEvalToBe("cos(10)", "Ok(-0.8390715290764524)")
    // TODO more built ins
  })
  describe("arrays", () => {
    test("empty array", () => expectEvalToBe("[]", "Ok([])"))
-    test("[1, 2, 3]", () => expectEvalToBe("[1, 2, 3]", "Ok([1, 2, 3])"))
-    test("['hello', 'world']", () => expectEvalToBe("['hello', 'world']", "Ok(['hello', 'world'])"))
-    test("index", () => expectEvalToBe("([0,1,2])[1]", "Ok(1)"))
-    test("index not found", () =>
-      expectEvalToBe("([0,1,2])[10]", "Error(Array index not found: 10)")
-    )
+    testEvalToBe("[1, 2, 3]", "Ok([1, 2, 3])")
+    testEvalToBe("['hello', 'world']", "Ok(['hello', 'world'])")
+    testEvalToBe("([0,1,2])[1]", "Ok(1)")
+    testDescriptionEvalToBe("index not found", "([0,1,2])[10]", "Error(Array index not found: 10)")
  })
  describe("records", () => {
    test("define", () => expectEvalToBe("{a: 1, b: 2}", "Ok({a: 1, b: 2})"))
    test("index", () => expectEvalToBe("{a: 1}.a", "Ok(1)"))
    test("index not found", () => expectEvalToBe("{a: 1}.b", "Error(Record property not found: b)"))
  })
+
+  describe("multi-line", () => {
+    testEvalToBe("1; 2", "Error(Assignment expected)")
+    testEvalToBe("1+1; 2+1", "Error(Assignment expected)")
+  })
+  describe("assignment", () => {
+    testEvalToBe("x=1; x", "Ok(1)")
+    testEvalToBe("x=1+1; x+1", "Ok(3)")
+    testEvalToBe("x=1; y=x+1; y+1", "Ok(3)")
+    testEvalToBe("1; x=1", "Error(Assignment expected)")
+    testEvalToBe("1; 1", "Error(Assignment expected)")
+    testEvalToBe("x=1; x=1", "Error(Expression expected)")
+  })
 })

 describe("test exceptions", () => {
-  test("javascript exception", () =>
-    expectEvalToBe("jsraise('div by 0')", "Error(JS Exception: Error: 'div by 0')")
+  testDescriptionEvalToBe(
+    "javascript exception",
+    "javascriptraise('div by 0')",
+    "Error(JS Exception: Error: 'div by 0')",
  )
-
-  test("rescript exception", () =>
-    expectEvalToBe("resraise()", "Error(TODO: unhandled rescript exception)")
+  testDescriptionEvalToBe(
+    "rescript exception",
+    "rescriptraise()",
+    "Error(TODO: unhandled rescript exception)",
  )
 })
--- a/packages/squiggle-lang/tests/ReducerInterface/ReducerInterface_Distribution_test.res
+++ b/packages/squiggle-lang/tests/ReducerInterface/ReducerInterface_Distribution_test.res
@ -111,7 +111,11 @@ describe("parse on distribution functions", () => {
  })
  describe("pointwise arithmetic expressions", () => {
    testParse(~skip=true, "normal(5,2) .+ normal(5,1)", "Ok((:dotAdd (:normal 5 2) (:normal 5 1)))")
-    testParse(~skip=true, "normal(5,2) .- normal(5,1)", "Ok((:dotSubtract (:normal 5 2) (:normal 5 1)))")
+    testParse(
+      ~skip=true,
+      "normal(5,2) .- normal(5,1)",
+      "Ok((:dotSubtract (:normal 5 2) (:normal 5 1)))",
+    )
    testParse("normal(5,2) .* normal(5,1)", "Ok((:dotMultiply (:normal 5 2) (:normal 5 1)))")
    testParse("normal(5,2) ./ normal(5,1)", "Ok((:dotDivide (:normal 5 2) (:normal 5 1)))")
    testParse("normal(5,2) .^ normal(5,1)", "Ok((:dotPow (:normal 5 2) (:normal 5 1)))")
--- a/packages/squiggle-lang/tests/TestHelpers.res
+++ b/packages/squiggle-lang/tests/TestHelpers.res
@ -6,7 +6,6 @@ let makeTest = (~only=false, str, item1, item2) =>
    ? Only.test(str, () => expect(item1)->toEqual(item2))
    : test(str, () => expect(item1)->toEqual(item2))

-
 let {toFloat, toDist, toString, toError, fmap} = module(DistributionOperation.Output)

 let fnImage = (theFn, inps) => Js.Array.map(theFn, inps)
@ -20,7 +19,9 @@ let run = DistributionOperation.run(~env)
 let outputMap = fmap(~env)
 let unreachableInTestFileMessage = "Should be impossible to reach (This error is in test file)"
 let toExtFloat: option<float> => float = E.O.toExt(unreachableInTestFileMessage)
-let toExtDist: option<GenericDist_Types.genericDist> => GenericDist_Types.genericDist = E.O.toExt(unreachableInTestFileMessage)
+let toExtDist: option<GenericDist_Types.genericDist> => GenericDist_Types.genericDist = E.O.toExt(
+  unreachableInTestFileMessage,
+)
 // let toExt: option<'a> => 'a = E.O.toExt(unreachableInTestFileMessage)
 let unpackFloat = x => x->toFloat->toExtFloat
 let unpackDist = y => y->toDist->toExtDist
--- a/packages/squiggle-lang/tests/XYShape_test.res
+++ b/packages/squiggle-lang/tests/XYShape_test.res
@ -21,7 +21,11 @@ let pointSetDist3: PointSetTypes.xyShape = {
 describe("XYShapes", () => {
  describe("logScorePoint", () => {
    makeTest("When identical", XYShape.logScorePoint(30, pointSetDist1, pointSetDist1), Some(0.0))
-    makeTest("When similar", XYShape.logScorePoint(30, pointSetDist1, pointSetDist2), Some(1.658971191043856))
+    makeTest(
+      "When similar",
+      XYShape.logScorePoint(30, pointSetDist1, pointSetDist2),
+      Some(1.658971191043856),
+    )
    makeTest(
      "When very different",
      XYShape.logScorePoint(30, pointSetDist1, pointSetDist3),
--- a/packages/squiggle-lang/src/js/index.ts
+++ b/packages/squiggle-lang/src/js/index.ts
@ -88,6 +88,7 @@ function tag<a, b>(x: a, y: b): tagged<a, b> {
 export type squiggleExpression =
  | tagged<"symbol", string>
  | tagged<"string", string>
+  | tagged<"call", string>
  | tagged<"array", squiggleExpression[]>
  | tagged<"boolean", boolean>
  | tagged<"distribution", Distribution>
@ -117,6 +118,8 @@ function createTsExport(
      );
    case "EvBool":
      return tag("boolean", x.value);
+    case "EvCall":
+      return tag("call", x.value);
    case "EvDistribution":
      return tag("distribution", new Distribution(x.value, sampEnv));
    case "EvNumber":
--- a/packages/squiggle-lang/src/rescript/Distributions/DistributionOperation/DistributionOperation.resi
+++ b/packages/squiggle-lang/src/rescript/Distributions/DistributionOperation/DistributionOperation.resi
@ -56,12 +56,7 @@ module Constructors: {
  @genType
  let toSampleSet: (~env: env, genericDist, int) => result<genericDist, error>
  @genType
-    let truncate: (
-      ~env: env,
-      genericDist,
-      option<float>,
-      option<float>,
-    ) => result<genericDist, error>
+  let truncate: (~env: env, genericDist, option<float>, option<float>) => result<genericDist, error>
  @genType
  let inspect: (~env: env, genericDist) => result<genericDist, error>
  @genType
--- a/packages/squiggle-lang/src/rescript/Distributions/DistributionTypes.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/DistributionTypes.res
@ -55,7 +55,11 @@ module DistributionOperation = {
  type fromDist =
    | ToFloat(Operation.toFloat)
    | ToDist(toDist)
-    | ToDistCombination(Operation.direction, Operation.arithmeticOperation, [#Dist(genericDist) | #Float(float)])
+    | ToDistCombination(
+        Operation.direction,
+        Operation.arithmeticOperation,
+        [#Dist(genericDist) | #Float(float)],
+      )
    | ToString

  type singleParamaterFunction =
--- a/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/AlgebraicShapeCombination.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/AlgebraicShapeCombination.res
@ -100,7 +100,6 @@ let combineShapesContinuousContinuous = (
  s1: PointSetTypes.xyShape,
  s2: PointSetTypes.xyShape,
 ): PointSetTypes.xyShape => {
-
  // if we add the two distributions, we should probably use normal filters.
  // if we multiply the two distributions, we should probably use lognormal filters.
  let t1m = toDiscretePointMassesFromTriangulars(s1)
--- a/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/Continuous.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/Continuous.res
@ -235,18 +235,10 @@ module T = Dist({
    let indefiniteIntegralStepwise = (p, h1) => h1 *. p ** 2.0 /. 2.0
    let indefiniteIntegralLinear = (p, a, b) => a *. p ** 2.0 /. 2.0 +. b *. p ** 3.0 /. 3.0

-    Analysis.integrate(
-      ~indefiniteIntegralStepwise,
-      ~indefiniteIntegralLinear,
-      t,
-    )
+    Analysis.integrate(~indefiniteIntegralStepwise, ~indefiniteIntegralLinear, t)
  }
  let variance = (t: t): float =>
-    XYShape.Analysis.getVarianceDangerously(
-      t,
-      mean,
-      Analysis.getMeanOfSquares,
-    )
+    XYShape.Analysis.getVarianceDangerously(t, mean, Analysis.getMeanOfSquares)
 })

 let downsampleEquallyOverX = (length, t): t =>
--- a/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/Mixed.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/Mixed.res
@ -212,8 +212,7 @@ module T = Dist({
    let totalIntegralSum = discreteIntegralSum +. continuousIntegralSum

    let getMeanOfSquares = ({discrete, continuous}: t) => {
-      let discreteMean =
-        discrete |> Discrete.shapeMap(XYShape.T.square) |> Discrete.T.mean
+      let discreteMean = discrete |> Discrete.shapeMap(XYShape.T.square) |> Discrete.T.mean
      let continuousMean = continuous |> Continuous.Analysis.getMeanOfSquares
      (discreteMean *. discreteIntegralSum +. continuousMean *. continuousIntegralSum) /.
        totalIntegralSum
--- a/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/PointSetTypes.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/PointSetDist/PointSetTypes.res
@ -14,10 +14,10 @@ type distributionType = [
  | #CDF
 ]

-type xyShape = XYShape.xyShape;
-type interpolationStrategy = XYShape.interpolationStrategy;
-type extrapolationStrategy = XYShape.extrapolationStrategy;
-type interpolator = XYShape.extrapolationStrategy;
+type xyShape = XYShape.xyShape
+type interpolationStrategy = XYShape.interpolationStrategy
+type extrapolationStrategy = XYShape.extrapolationStrategy
+type interpolator = XYShape.extrapolationStrategy

@genType
 type rec continuousShape = {
--- a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
@ -346,7 +346,11 @@ module T = {
    | _ => #NoSolution
    }

-  let toPointSetDist = (~xSelection=#ByWeight, sampleCount, d: symbolicDist): PointSetTypes.pointSetDist =>
+  let toPointSetDist = (
+    ~xSelection=#ByWeight,
+    sampleCount,
+    d: symbolicDist,
+  ): PointSetTypes.pointSetDist =>
    switch d {
    | #Float(v) => Discrete(Discrete.make(~integralSumCache=Some(1.0), {xs: [v], ys: [1.0]}))
    | _ =>
--- a/packages/squiggle-lang/src/rescript/OldInterpreter/typeSystem/HardcodedFunctions.res
+++ b/packages/squiggle-lang/src/rescript/OldInterpreter/typeSystem/HardcodedFunctions.res
@ -22,7 +22,7 @@ let makeSymbolicFromTwoFloats = (name, fn) =>
    ~inputTypes=[#Float, #Float],
    ~run=x =>
      switch x {
-      | [#Float(a), #Float(b)] => fn(a, b) |> E.R.fmap(r => (#SymbolicDist(r)))
+      | [#Float(a), #Float(b)] => fn(a, b) |> E.R.fmap(r => #SymbolicDist(r))
      | e => wrongInputsError(e)
      },
    (),
@ -90,7 +90,8 @@ let floatFromDist = (
  switch t {
  | #SymbolicDist(s) =>
    SymbolicDist.T.operate(distToFloatOp, s) |> E.R.bind(_, v => Ok(#SymbolicDist(#Float(v))))
-  | #RenderedDist(rs) => PointSetDist.operate(distToFloatOp, rs) |> (v => Ok(#SymbolicDist(#Float(v))))
+  | #RenderedDist(rs) =>
+    PointSetDist.operate(distToFloatOp, rs) |> (v => Ok(#SymbolicDist(#Float(v))))
  }

 let verticalScaling = (scaleOp, rs, scaleBy) => {
@ -126,9 +127,14 @@ module Multimodal = {
        ->E.R.bind(r => r |> E.A.fmap(TypeSystem.TypedValue.toFloat) |> E.A.R.firstErrorOrOpen)

      E.R.merge(dists, weights)->E.R.bind(((a, b)) =>
-          E.A.length(b) > E.A.length(a) ?
-            Error("Too many weights provided") :
-            Ok(E.A.zipMaxLength(a, b) |> E.A.fmap(((a, b)) => (a |> E.O.toExn(""), b |> E.O.default(1.0))))
+        E.A.length(b) > E.A.length(a)
+          ? Error("Too many weights provided")
+          : Ok(
+              E.A.zipMaxLength(a, b) |> E.A.fmap(((a, b)) => (
+                a |> E.O.toExn(""),
+                b |> E.O.default(1.0),
+              )),
+            )
      )
    | _ => Error("Needs items")
    }
--- a/packages/squiggle-lang/src/rescript/OldInterpreter/typeSystem/TypeSystem.res
+++ b/packages/squiggle-lang/src/rescript/OldInterpreter/typeSystem/TypeSystem.res
@ -86,11 +86,7 @@ module TypedValue = {
      |> E.R.fmap(r => #Array(r))
    | (#Hash(named), #Hash(r)) =>
      let keyValues =
-        named |> E.A.fmap(((name, intendedType)) => (
-          name,
-          intendedType,
-          Hash.getByName(r, name),
-        ))
+        named |> E.A.fmap(((name, intendedType)) => (name, intendedType, Hash.getByName(r, name)))
      let typedHash =
        keyValues
        |> E.A.fmap(((name, intendedType, optionNode)) =>
@ -180,11 +176,7 @@ module Function = {
        _coerceInputNodes(evaluationParams, t.inputTypes, t.shouldCoerceTypes),
      )

-    let run = (
-      evaluationParams: ASTTypes.evaluationParams,
-      inputNodes: inputNodes,
-      t: t,
-    ) =>
+    let run = (evaluationParams: ASTTypes.evaluationParams, inputNodes: inputNodes, t: t) =>
      inputsToTypedValues(evaluationParams, inputNodes, t)->E.R.bind(t.run)
        |> (
          x =>
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
@ -6,7 +6,7 @@ module Js = Reducer_Js
 module MathJs = Reducer_MathJs

@genType
-type expressionValue = Reducer_Expression.expressionValue
+type expressionValue = ReducerInterface_ExpressionValue.expressionValue

@genType
 let evaluate: string => result<expressionValue, Reducer_ErrorValue.errorValue>
--- 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
@ -14,8 +14,8 @@ exception TestRescriptException
 let callInternal = (call: functionCall): result<'b, errorValue> => {
  let callMathJs = (call: functionCall): result<'b, errorValue> =>
    switch call {
-    | ("jsraise", [msg]) => Js.Exn.raiseError(toString(msg)) // For Tests
-    | ("resraise", _) => raise(TestRescriptException) // For Tests
+    | ("javascriptraise", [msg]) => Js.Exn.raiseError(toString(msg)) // For Tests
+    | ("rescriptraise", _) => raise(TestRescriptException) // For Tests
    | call => call->toStringFunctionCall->MathJs.Eval.eval
    }

@ -58,7 +58,7 @@ let callInternal = (call: functionCall): result<'b, errorValue> => {
 }

 /*
-  Lisp engine uses Result monad while reducing expressions
+  Reducer uses Result monad while reducing expressions
 */
 let dispatch = (call: functionCall): result<expressionValue, errorValue> =>
  try {
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
@ -1,9 +1,14 @@
@genType
 type errorValue =
  | REArrayIndexNotFound(string, int)
+  | REAssignmentExpected
+  | REExpressionExpected
  | REFunctionExpected(string)
  | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
+  | REMacroNotFound(string)
  | RERecordPropertyNotFound(string, string)
+  | RESymbolNotFound(string)
+  | RESyntaxError(string)
  | RETodo(string) // To do

 type t = errorValue
@ -12,6 +17,8 @@ type t = errorValue
 let errorToString = err =>
  switch err {
  | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
+  | REAssignmentExpected => "Assignment expected"
+  | REExpressionExpected => "Expression expected"
  | REFunctionExpected(msg) => `Function expected: ${msg}`
  | REJavaScriptExn(omsg, oname) => {
      let answer = "JS Exception:"
@ -25,6 +32,9 @@ let errorToString = err =>
      }
      answer
    }
+  | REMacroNotFound(macro) => `Macro not found: ${macro}`
  | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
+  | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
+  | RESyntaxError(desc) => `Syntax Error: ${desc}`
  | RETodo(msg) => `TODO: ${msg}`
  }
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
@ -11,10 +11,11 @@ type expressionValue = ExpressionValue.expressionValue
 type t = expression

 /*
-  Shows the Lisp Code as text lisp code
+  Shows the expression as text of expression
 */
 let rec toString = expression =>
  switch expression {
+  | T.EBindings(bindings) => "$$bound"
  | T.EList(aList) =>
    `(${Belt.List.map(aList, aValue => toString(aValue))
      ->Extra.List.interperse(" ")
@ -30,7 +31,7 @@ let toStringResult = codeResult =>
  }

 /*
-  Converts a MathJs code to Lisp Code
+  Converts a MathJs code to expression
 */
 let parse_ = (expr: string, parser, converter): result<t, errorValue> =>
  expr->parser->Result.flatMap(node => converter(node))
@ -38,24 +39,105 @@ let parse_ = (expr: string, parser, converter): result<t, errorValue> =>
 let parse = (mathJsCode: string): result<t, errorValue> =>
  mathJsCode->parse_(MathJs.Parse.parse, MathJs.ToExpression.fromNode)

-module MapString = Belt.Map.String
-type bindings = MapString.t<unit>
-let defaultBindings: bindings = MapString.fromArray([])
-// TODO Define bindings for function execution context
+let defaultBindings: T.bindings = Belt.Map.String.empty

 /*
-  After reducing each level of code tree, we have a value list to evaluate
+  Recursively evaluate/reduce the expression (Lisp AST)
+*/
+let rec reduceExpression = (expression: t, bindings: T.bindings): result<expressionValue, 'e> => {
+  /*
+    After reducing each level of expression(Lisp AST), we have a value list to evaluate
 */
  let reduceValueList = (valueList: list<expressionValue>): result<expressionValue, 'e> =>
    switch valueList {
-  | list{EvSymbol(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch
+    | list{EvCall(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch
    | _ => valueList->Belt.List.toArray->ExpressionValue.EvArray->Ok
    }

  /*
-  Recursively evaluate/reduce the code tree
+    Macros are like functions but instead of taking values as parameters,
+    they take expressions as parameters and return a new expression.
+    Macros are used to define language building blocks. They are like Lisp macros.
 */
-let rec reduceExpression = (expression: t, bindings): result<expressionValue, 'e> =>
+  let doMacroCall = (list: list<t>, bindings: T.bindings): result<t, 'e> => {
+    let dispatchMacroCall = (list: list<t>, bindings: T.bindings): result<t, 'e> => {
+      let rec replaceSymbols = (expression: t, bindings: T.bindings): result<t, errorValue> =>
+        switch expression {
+        | T.EValue(EvSymbol(aSymbol)) =>
+          switch bindings->Belt.Map.String.get(aSymbol) {
+          | Some(boundExpression) => boundExpression->Ok
+          | None => RESymbolNotFound(aSymbol)->Error
+          }
+        | T.EValue(_) => expression->Ok
+        | T.EBindings(_) => expression->Ok
+        | T.EList(list) => {
+            let racc = list->Belt.List.reduceReverse(Ok(list{}), (racc, each: expression) =>
+              racc->Result.flatMap(acc => {
+                each
+                ->replaceSymbols(bindings)
+                ->Result.flatMap(newNode => {
+                  acc->Belt.List.add(newNode)->Ok
+                })
+              })
+            )
+            racc->Result.map(acc => acc->T.EList)
+          }
+        }
+
+      let doBindStatement = (statement: t, bindings: T.bindings) => {
+        switch statement {
+        | T.EList(list{T.EValue(EvCall("$let")), T.EValue(EvSymbol(aSymbol)), expression}) => {
+            let rNewExpression = replaceSymbols(expression, bindings)
+            rNewExpression->Result.map(newExpression =>
+              Belt.Map.String.set(bindings, aSymbol, newExpression)->T.EBindings
+            )
+          }
+        | _ => REAssignmentExpected->Error
+        }
+      }
+
+      let doBindExpression = (expression: t, bindings: T.bindings) => {
+        switch expression {
+        | T.EList(list{T.EValue(EvCall("$let")), ..._}) => REExpressionExpected->Error
+        | _ => replaceSymbols(expression, bindings)
+        }
+      }
+
+      switch list {
+      | list{T.EValue(EvCall("$$bindings"))} => bindings->T.EBindings->Ok
+
+      | list{T.EValue(EvCall("$$bindStatement")), T.EBindings(bindings), statement} =>
+        doBindStatement(statement, bindings)
+      | list{T.EValue(EvCall("$$bindExpression")), T.EBindings(bindings), expression} =>
+        doBindExpression(expression, bindings)
+      | _ => list->T.EList->Ok
+      }
+    }
+
+    list->dispatchMacroCall(bindings)
+  }
+
+  let rec seekMacros = (expression: t, bindings: T.bindings): result<t, 'e> =>
+    switch expression {
+    | T.EValue(value) => expression->Ok
+    | T.EList(list) => {
+        let racc: result<list<t>, 'e> = list->Belt.List.reduceReverse(Ok(list{}), (
+          racc,
+          each: expression,
+        ) =>
+          racc->Result.flatMap(acc => {
+            each
+            ->seekMacros(bindings)
+            ->Result.flatMap(newNode => {
+              acc->Belt.List.add(newNode)->Ok
+            })
+          })
+        )
+        racc->Result.flatMap(acc => acc->doMacroCall(bindings))
+      }
+    }
+
+  let rec reduceExpandedExpression = (expression: t): result<expressionValue, 'e> =>
    switch expression {
    | T.EValue(value) => value->Ok
    | T.EList(list) => {
@ -65,7 +147,7 @@ let rec reduceExpression = (expression: t, bindings): result<expressionValue, 'e
        ) =>
          racc->Result.flatMap(acc => {
            each
-          ->reduceExpression(bindings)
+            ->reduceExpandedExpression
            ->Result.flatMap(newNode => {
              acc->Belt.List.add(newNode)->Ok
            })
@ -75,17 +157,23 @@ let rec reduceExpression = (expression: t, bindings): result<expressionValue, 'e
      }
    }

+  let rExpandedExpression: result<t, 'e> = expression->seekMacros(bindings)
+  rExpandedExpression->Result.flatMap(expandedExpression =>
+    expandedExpression->reduceExpandedExpression
+  )
+}
+
 let evalWBindingsExpression = (aExpression, bindings): result<expressionValue, 'e> =>
  reduceExpression(aExpression, bindings)

 /*
-  Evaluates MathJs code via Lisp using bindings and answers the result
+  Evaluates MathJs code via Reducer using bindings and answers the result
 */
-let evalWBindings = (codeText: string, bindings: bindings) => {
+let evalWBindings = (codeText: string, bindings: T.bindings) => {
  parse(codeText)->Result.flatMap(code => code->evalWBindingsExpression(bindings))
 }

 /*
-  Evaluates MathJs code via Lisp and answers the result
+  Evaluates MathJs code via Reducer and answers the result
 */
 let eval = (code: string) => evalWBindings(code, defaultBindings)
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.resi
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.resi
@ -1,29 +0,0 @@
-module Result = Belt.Result
-module T = Reducer_Expression_T
-type expression = T.expression
-@genType
-type expressionValue = ReducerInterface_ExpressionValue.expressionValue
-type t = expression
-let toString: T.expression => Js.String.t
-let toStringResult: result<T.expression, 'a> => string
-let parse: string => result<expression, Reducer_ErrorValue.t>
-module MapString = Belt.Map.String
-type bindings = MapString.t<unit>
-let defaultBindings: bindings
-let reduceValueList: list<expressionValue> => result<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let reduceExpression: (expression, 'a) => result<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let evalWBindingsExpression: (expression, 'a) => result<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let evalWBindings: (string, bindings) => Result.t<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let eval: string => Result.t<expressionValue, Reducer_ErrorValue.t>
--- 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
@ -1,5 +1,15 @@
 open ReducerInterface.ExpressionValue

+/*
+  An expression is a Lisp AST. An expression is either a primitive value or a list of expressions.
+  In the case of a list of expressions (e1, e2, e3, ...eN), the semantic is
+     apply e1, e2 -> apply e3 -> ... -> apply eN
+  This is Lisp semantics. It holds true in both eager and lazy evaluations.
+  A Lisp AST contains only expressions/primitive values to apply to their left.
+  The act of defining the semantics of a functional language is to write it in terms of Lisp AST.
+*/
 type rec expression =
  | EList(list<expression>) // A list to map-reduce
  | EValue(expressionValue) // Irreducible built-in value. Reducer should not know the internals. External libraries are responsible
+  | EBindings(bindings) // let/def kind of statements return bindings
+and bindings = Belt.Map.String.t<expression>
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_MathJs/Reducer_MathJs_Parse.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_MathJs/Reducer_MathJs_Parse.res
@ -7,25 +7,31 @@ open Reducer_ErrorValue

 type node = {"type": string, "isNode": bool, "comment": string}
 type arrayNode = {...node, "items": array<node>}
-//assignmentNode
-//blockNode
+type block = {"node": node}
+type blockNode = {...node, "blocks": array<block>}
 //conditionalNode
 type constantNode = {...node, "value": unit}
 //functionAssignmentNode
-type functionNode = {...node, "fn": string, "args": array<node>}
 type indexNode = {...node, "dimensions": array<node>}
 type objectNode = {...node, "properties": Js.Dict.t<node>}
-type accessorNode = {...node, "object": node, "index": indexNode}
-type operatorNode = {...functionNode, "op": string}
+type accessorNode = {...node, "object": node, "index": indexNode, "name": string}

-//parenthesisNode
 type parenthesisNode = {...node, "content": node}
 //rangeNode
 //relationalNode
 type symbolNode = {...node, "name": string}
+type functionNode = {...node, "fn": unit, "args": array<node>}
+type operatorNode = {...functionNode, "op": string}
+type assignmentNode = {...node, "object": symbolNode, "value": node}
+type assignmentNodeWAccessor = {...node, "object": accessorNode, "value": node}
+type assignmentNodeWIndex = {...assignmentNodeWAccessor, "index": Js.null<indexNode>}

 external castAccessorNode: node => accessorNode = "%identity"
 external castArrayNode: node => arrayNode = "%identity"
+external castAssignmentNode: node => assignmentNode = "%identity"
+external castAssignmentNodeWAccessor: node => assignmentNodeWAccessor = "%identity"
+external castAssignmentNodeWIndex: node => assignmentNodeWIndex = "%identity"
+external castBlockNode: node => blockNode = "%identity"
 external castConstantNode: node => constantNode = "%identity"
 external castFunctionNode: node => functionNode = "%identity"
 external castIndexNode: node => indexNode = "%identity"
@ -50,6 +56,8 @@ let parse = (expr: string): result<node, errorValue> =>
 type mathJsNode =
  | MjAccessorNode(accessorNode)
  | MjArrayNode(arrayNode)
+  | MjAssignmentNode(assignmentNode)
+  | MjBlockNode(blockNode)
  | MjConstantNode(constantNode)
  | MjFunctionNode(functionNode)
  | MjIndexNode(indexNode)
@ -58,10 +66,21 @@ type mathJsNode =
  | MjParenthesisNode(parenthesisNode)
  | MjSymbolNode(symbolNode)

-let castNodeType = (node: node) =>
+let castNodeType = (node: node) => {
+  let decideAssignmentNode = node => {
+    let iNode = node->castAssignmentNodeWIndex
+    if Js.null == iNode["index"] && iNode["object"]["type"] == "SymbolNode" {
+      node->castAssignmentNode->MjAssignmentNode->Ok
+    } else {
+      RESyntaxError("Assignment to index or property not supported")->Error
+    }
+  }
+
  switch node["type"] {
  | "AccessorNode" => node->castAccessorNode->MjAccessorNode->Ok
  | "ArrayNode" => node->castArrayNode->MjArrayNode->Ok
+  | "AssignmentNode" => node->decideAssignmentNode
+  | "BlockNode" => node->castBlockNode->MjBlockNode->Ok
  | "ConstantNode" => node->castConstantNode->MjConstantNode->Ok
  | "FunctionNode" => node->castFunctionNode->MjFunctionNode->Ok
  | "IndexNode" => node->castIndexNode->MjIndexNode->Ok
@ -71,6 +90,19 @@ let castNodeType = (node: node) =>
  | "SymbolNode" => node->castSymbolNode->MjSymbolNode->Ok
  | _ => RETodo(`Argg, unhandled MathJsNode: ${node["type"]}`)->Error
  }
+}
+
+external unitAsSymbolNode: unit => symbolNode = "%identity"
+external unitAsString: unit => string = "%identity"
+
+let nameOfFunctionNode = (fNode: functionNode): string => {
+  let name = fNode["fn"]
+  if Js.typeof(name) == "string" {
+    name->unitAsString
+  } else {
+    (name->unitAsSymbolNode)["name"]
+  }
+}

 let rec toString = (mathJsNode: mathJsNode): string => {
  let toStringValue = (a: 'a): string =>
@ -87,9 +119,10 @@ let rec toString = (mathJsNode: mathJsNode): string => {
    ->Js.String.concatMany("")

  let toStringFunctionNode = (fnode: functionNode): string =>
-    `${fnode["fn"]}(${fnode["args"]->toStringNodeArray})`
+    `${fnode->nameOfFunctionNode}(${fnode["args"]->toStringNodeArray})`

-  let toStringObjectEntry = ((key: string, value: node)): string => `${key}: ${value->toStringMathJsNode}`
+  let toStringObjectEntry = ((key: string, value: node)): string =>
+    `${key}: ${value->toStringMathJsNode}`

  let toStringObjectNode = (oNode: objectNode): string =>
    `{${oNode["properties"]
@ -103,16 +136,28 @@ let rec toString = (mathJsNode: mathJsNode): string => {
    ->Belt.Array.map(each => toStringResult(each->castNodeType))
    ->Js.String.concatMany("")

+  let toStringSymbolNode = (sNode: symbolNode): string => sNode["name"]
+
+  let toStringBlocks = (blocks: array<block>): string =>
+    blocks
+    ->Belt.Array.map(each => each["node"]->castNodeType->toStringResult)
+    ->Extra.Array.interperse("; ")
+    ->Js.String.concatMany("")
+
  switch mathJsNode {
-  | MjAccessorNode(aNode) => `${aNode["object"]->toStringMathJsNode}[${aNode["index"]->toStringIndexNode}]`
+  | MjAccessorNode(aNode) =>
+    `${aNode["object"]->toStringMathJsNode}[${aNode["index"]->toStringIndexNode}]`
  | MjArrayNode(aNode) => `[${aNode["items"]->toStringNodeArray}]`
+  | MjAssignmentNode(aNode) =>
+    `${aNode["object"]->toStringSymbolNode} = ${aNode["value"]->toStringMathJsNode}`
+  | MjBlockNode(bNode) => `{${bNode["blocks"]->toStringBlocks}}`
  | MjConstantNode(cNode) => cNode["value"]->toStringValue
  | MjFunctionNode(fNode) => fNode->toStringFunctionNode
  | MjIndexNode(iNode) => iNode->toStringIndexNode
  | MjObjectNode(oNode) => oNode->toStringObjectNode
  | MjOperatorNode(opNode) => opNode->castOperatorNodeToFunctionNode->toStringFunctionNode
  | MjParenthesisNode(pNode) => `(${toStringMathJsNode(pNode["content"])})`
-  | MjSymbolNode(sNode) => sNode["name"]
+  | MjSymbolNode(sNode) => sNode->toStringSymbolNode
  }
 }
 and toStringResult = (rMathJsNode: result<mathJsNode, errorValue>): string =>
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_MathJs/Reducer_MathJs_ToExpression.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_MathJs/Reducer_MathJs_ToExpression.res
@ -1,11 +1,11 @@
 module ErrorValue = Reducer_ErrorValue
 module ExpressionValue = ReducerInterface.ExpressionValue
-module ExtressionT = Reducer_Expression_T
+module ExpressionT = Reducer_Expression_T
 module JavaScript = Reducer_Js
 module Parse = Reducer_MathJs_Parse
 module Result = Belt.Result

-type expression = ExtressionT.expression
+type expression = ExpressionT.expression
 type expressionValue = ExpressionValue.expressionValue
 type errorValue = ErrorValue.errorValue

@ -18,10 +18,19 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
        )
      )

-    let castFunctionNode = fNode => {
-      let fn = fNode["fn"]->ExpressionValue.EvSymbol->ExtressionT.EValue
+    let toEvCallValue = (name: string): expression =>
+      name->ExpressionValue.EvCall->ExpressionT.EValue
+    let toEvSymbolValue = (name: string): expression =>
+      name->ExpressionValue.EvSymbol->ExpressionT.EValue
+
+    let passToFunction = (fName: string, rLispArgs): result<expression, errorValue> => {
+      let fn = fName->toEvCallValue
+      rLispArgs->Result.flatMap(lispArgs => list{fn, ...lispArgs}->ExpressionT.EList->Ok)
+    }
+
+    let caseFunctionNode = fNode => {
      let lispArgs = fNode["args"]->Belt.List.fromArray->fromNodeList
-      lispArgs->Result.map(argsCode => list{fn, ...argsCode}->ExtressionT.EList)
+      passToFunction(fNode->Parse.nameOfFunctionNode, lispArgs)
    }

    let caseObjectNode = oNode => {
@ -34,15 +43,16 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
            fromNode(value)->Result.map(valueExpression => {
              let entryCode =
                list{
-                  key->ExpressionValue.EvString->ExtressionT.EValue,
+                  key->ExpressionValue.EvString->ExpressionT.EValue,
                  valueExpression,
-                }->ExtressionT.EList
+                }->ExpressionT.EList
              list{entryCode, ...acc}
            })
          )
        )
-        let lispName = "$constructRecord"->ExpressionValue.EvSymbol->ExtressionT.EValue
-        rargs->Result.map(args => list{lispName, ExtressionT.EList(args)}->ExtressionT.EList)
+        rargs->Result.flatMap(args =>
+          passToFunction("$constructRecord", list{ExpressionT.EList(args)}->Ok)
+        ) // $consturctRecord gets a single argument: List of key-value paiers
      }

      oNode["properties"]->Js.Dict.entries->Belt.List.fromArray->fromObjectEntries
@ -54,33 +64,75 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
        Ok(list{}),
        (racc, currentPropertyMathJsNode) =>
          racc->Result.flatMap(acc =>
-            fromNode(currentPropertyMathJsNode)->Result.map(propertyCode => list{propertyCode, ...acc})
+            fromNode(currentPropertyMathJsNode)->Result.map(propertyCode => list{
+              propertyCode,
+              ...acc,
+            })
          ),
      )
-      rpropertyCodeList->Result.map(propertyCodeList => ExtressionT.EList(propertyCodeList))
+      rpropertyCodeList->Result.map(propertyCodeList => ExpressionT.EList(propertyCodeList))
    }

    let caseAccessorNode = (objectNode, indexNode) => {
-      let fn = "$atIndex"->ExpressionValue.EvSymbol->ExtressionT.EValue
-
      caseIndexNode(indexNode)->Result.flatMap(indexCode => {
-        fromNode(objectNode)->Result.map(objectCode =>
-          list{fn, objectCode, indexCode}->ExtressionT.EList
+        fromNode(objectNode)->Result.flatMap(objectCode =>
+          passToFunction("$atIndex", list{objectCode, indexCode}->Ok)
        )
      })
    }

-    switch typedMathJsNode {
-    | MjArrayNode(aNode) =>
-      aNode["items"]->Belt.List.fromArray->fromNodeList->Result.map(list => ExtressionT.EList(list))
-    | MjConstantNode(cNode) =>
-      cNode["value"]->JavaScript.Gate.jsToEv->Result.map(v => v->ExtressionT.EValue)
-    | MjFunctionNode(fNode) => fNode->castFunctionNode
-    | MjOperatorNode(opNode) => opNode->Parse.castOperatorNodeToFunctionNode->castFunctionNode
-    | MjParenthesisNode(pNode) => pNode["content"]->fromNode
-    | MjAccessorNode(aNode) => caseAccessorNode(aNode["object"], aNode["index"])
-    | MjObjectNode(oNode) => caseObjectNode(oNode)
-    | MjSymbolNode(sNode) => sNode["name"]->ExpressionValue.EvSymbol->ExtressionT.EValue->Ok
-    | MjIndexNode(iNode) => caseIndexNode(iNode)
-    }
+    let caseAssignmentNode = aNode => {
+      let symbol = aNode["object"]["name"]->toEvSymbolValue
+      let rValueExpression = fromNode(aNode["value"])
+      rValueExpression->Result.flatMap(valueExpression => {
+        let lispArgs = list{symbol, valueExpression}->Ok
+        passToFunction("$let", lispArgs)
+      })
+    }
+
+    let caseArrayNode = aNode => {
+      aNode["items"]->Belt.List.fromArray->fromNodeList->Result.map(list => ExpressionT.EList(list))
+    }
+
+    let caseBlockNode = (bNode): result<expression, errorValue> => {
+      let blocks = bNode["blocks"]
+      let initialBindings = passToFunction("$$bindings", list{}->Ok)
+      let lastIndex = Belt.Array.length(blocks) - 1
+      blocks->Belt.Array.reduceWithIndex(initialBindings, (rPreviousBindings, block, i) => {
+        rPreviousBindings->Result.flatMap(previousBindings => {
+          let node = block["node"]
+          let rStatement: result<expression, errorValue> = node->fromNode
+          let bindName = if i == lastIndex {
+            "$$bindExpression"
+          } else {
+            "$$bindStatement"
+          }
+          rStatement->Result.flatMap((statement: expression) => {
+            let lispArgs = list{previousBindings, statement}->Ok
+            passToFunction(bindName, lispArgs)
+          })
+        })
+      })
+    }
+
+    let rFinalExpression: result<expression, errorValue> = switch typedMathJsNode {
+    | MjAccessorNode(aNode) => caseAccessorNode(aNode["object"], aNode["index"])
+    | MjArrayNode(aNode) => caseArrayNode(aNode)
+    | MjAssignmentNode(aNode) => caseAssignmentNode(aNode)
+    | MjSymbolNode(sNode) => {
+        let expr: expression = toEvSymbolValue(sNode["name"])
+        let rExpr: result<expression, errorValue> = expr->Ok
+        rExpr
+      }
+    | MjBlockNode(bNode) => caseBlockNode(bNode)
+    // | MjBlockNode(bNode) => "statement"->toEvSymbolValue->Ok
+    | MjConstantNode(cNode) =>
+      cNode["value"]->JavaScript.Gate.jsToEv->Result.flatMap(v => v->ExpressionT.EValue->Ok)
+    | MjFunctionNode(fNode) => fNode->caseFunctionNode
+    | MjIndexNode(iNode) => caseIndexNode(iNode)
+    | MjObjectNode(oNode) => caseObjectNode(oNode)
+    | MjOperatorNode(opNode) => opNode->Parse.castOperatorNodeToFunctionNode->caseFunctionNode
+    | MjParenthesisNode(pNode) => pNode["content"]->fromNode
+    }
+    rFinalExpression
  })
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
@ -7,25 +7,30 @@ module ErrorValue = Reducer_ErrorValue

@genType
 type rec expressionValue =
+  | EvArray(array<expressionValue>)
  | EvBool(bool)
+  | EvCall(string) // External function call
+  | EvDistribution(GenericDist_Types.genericDist)
  | EvNumber(float)
+  | EvRecord(Js.Dict.t<expressionValue>)
  | EvString(string)
  | EvSymbol(string)
-  | EvArray(array<expressionValue>)
-  | EvRecord(Js.Dict.t<expressionValue>)
-  | EvDistribution(GenericDist_Types.genericDist)

 type functionCall = (string, array<expressionValue>)

 let rec toString = aValue =>
  switch aValue {
  | EvBool(aBool) => Js.String.make(aBool)
+  | EvCall(fName) => `:${fName}`
  | EvNumber(aNumber) => Js.String.make(aNumber)
  | EvString(aString) => `'${aString}'`
  | EvSymbol(aString) => `:${aString}`
  | EvArray(anArray) => {
      let args =
-        anArray->Belt.Array.map(each => toString(each))->Extra_Array.interperse(", ")->Js.String.concatMany("")
+        anArray
+        ->Belt.Array.map(each => toString(each))
+        ->Extra_Array.interperse(", ")
+        ->Js.String.concatMany("")
      `[${args}]`
    }
  | EvRecord(aRecord) => {
@ -37,12 +42,13 @@ let rec toString = aValue =>
        ->Js.String.concatMany("")
      `{${pairs}}`
    }
-  | EvDistribution(dist) => `${GenericDist.toString(dist)}`
+  | EvDistribution(dist) => GenericDist.toString(dist)
  }

 let toStringWithType = aValue =>
  switch aValue {
  | EvBool(_) => `Bool::${toString(aValue)}`
+  | EvCall(_) => `Call::${toString(aValue)}`
  | EvNumber(_) => `Number::${toString(aValue)}`
  | EvString(_) => `String::${toString(aValue)}`
  | EvSymbol(_) => `Symbol::${toString(aValue)}`
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.res
@ -160,7 +160,8 @@ let dispatchToGenericOutput = (call: ExpressionValue.functionCall): option<
  | ("mean", [EvDistribution(dist)]) => Helpers.toFloatFn(#Mean, dist)
  | ("toString", [EvDistribution(dist)]) => Helpers.toStringFn(ToString, dist)
  | ("toSparkline", [EvDistribution(dist)]) => Helpers.toStringFn(ToSparkline(20), dist)
-  | ("toSparkline", [EvDistribution(dist), EvNumber(n)]) => Helpers.toStringFn(ToSparkline(Belt.Float.toInt(n)), dist)
+  | ("toSparkline", [EvDistribution(dist), EvNumber(n)]) =>
+    Helpers.toStringFn(ToSparkline(Belt.Float.toInt(n)), dist)
  | ("exp", [EvDistribution(a)]) =>
    // https://mathjs.org/docs/reference/functions/exp.html
    Helpers.twoDiststoDistFn(Algebraic, "pow", GenericDist.fromFloat(Math.e), a)->Some
--- a/packages/squiggle-lang/src/rescript/TypescriptInterface.res
+++ b/packages/squiggle-lang/src/rescript/TypescriptInterface.res
@ -32,7 +32,7 @@ let makeSampleSetDist = SampleSetDist.make
 let evaluate = Reducer.evaluate

@genType
-type expressionValue = Reducer_Expression.expressionValue
+type expressionValue = ReducerInterface_ExpressionValue.expressionValue

@genType
 type errorValue = Reducer_ErrorValue.errorValue
--- a/packages/squiggle-lang/src/rescript/Utility/E.res
+++ b/packages/squiggle-lang/src/rescript/Utility/E.res
@ -183,7 +183,8 @@ module R2 = {
  let bind = (a, b) => R.bind(b, a)

  //Converts result type to change error type only
-  let errMap = (a, map) => switch(a){
+  let errMap = (a, map) =>
+    switch a {
    | Ok(r) => Ok(r)
    | Error(e) => map(e)
    }
@ -300,7 +301,6 @@ module A = {
      |> Rationale.Result.return
    }

-
  // This zips while taking the longest elements of each array.
  let zipMaxLength = (array1, array2) => {
    let maxLength = Int.max(length(array1), length(array2))
@ -456,7 +456,6 @@ module A = {
    let diff = (arr: array<float>): array<float> =>
      Belt.Array.zipBy(arr, Belt.Array.sliceToEnd(arr, 1), (left, right) => right -. left)

-
    exception RangeError(string)
    let range = (min: float, max: float, n: int): array<float> =>
      switch n {
--- a/packages/squiggle-lang/src/rescript/Utility/Jstat.res
+++ b/packages/squiggle-lang/src/rescript/Utility/Jstat.res
@ -36,8 +36,8 @@ module Exponential = {
  @module("jstat") @scope("exponential") external pdf: (float, float) => float = "pdf"
  @module("jstat") @scope("exponential") external cdf: (float, float) => float = "cdf"
  @module("jstat") @scope("exponential") external inv: (float, float) => float = "inv"
-  @module("jstat") @scope("exponential") external sample: (float) => float = "sample"
-  @module("jstat") @scope("exponential") external mean: (float) => float = "mean"
+  @module("jstat") @scope("exponential") external sample: float => float = "sample"
+  @module("jstat") @scope("exponential") external mean: float => float = "mean"
 }

 module Cauchy = {
@ -56,7 +56,6 @@ module Triangular = {
  @module("jstat") @scope("triangular") external mean: (float, float, float) => float = "mean"
 }

-
 module Pareto = {
  @module("jstat") @scope("pareto") external pdf: (float, float, float) => float = "pdf"
  @module("jstat") @scope("pareto") external cdf: (float, float, float) => float = "cdf"
@ -66,8 +65,8 @@ module Pareto = {
 module Poisson = {
  @module("jstat") @scope("poisson") external pdf: (float, float) => float = "pdf"
  @module("jstat") @scope("poisson") external cdf: (float, float) => float = "cdf"
-  @module("jstat") @scope("poisson") external sample: (float) => float = "sample"
-  @module("jstat") @scope("poisson") external mean: (float) => float = "mean"
+  @module("jstat") @scope("poisson") external sample: float => float = "sample"
+  @module("jstat") @scope("poisson") external mean: float => float = "mean"
 }

 module Weibull = {
--- a/yarn.lock
+++ b/yarn.lock
@ -4142,7 +4142,7 @@
    "@types/source-list-map" "*"
    source-map "^0.7.3"

-"@types/webpack@^4.41.26", "@types/webpack@^4.41.32", "@types/webpack@^4.41.8":
+"@types/webpack@^4.41.26", "@types/webpack@^4.41.8":
  version "4.41.32"
  resolved "https://registry.yarnpkg.com/@types/webpack/-/webpack-4.41.32.tgz#a7bab03b72904070162b2f169415492209e94212"
  integrity sha512-cb+0ioil/7oz5//7tZUSwbrSAN/NWHrQylz5cW8G0dWTcF/g+/dSdMlKVZspBYuMAN1+WnwHrkxiRrLcwd0Heg==
@ -4154,6 +4154,15 @@
    anymatch "^3.0.0"
    source-map "^0.6.0"

+"@types/webpack@^5.28.0":
+  version "5.28.0"
+  resolved "https://registry.yarnpkg.com/@types/webpack/-/webpack-5.28.0.tgz#78dde06212f038d77e54116cfe69e88ae9ed2c03"
+  integrity sha512-8cP0CzcxUiFuA9xGJkfeVpqmWTk9nx6CWwamRGCj95ph1SmlRRk9KlCZ6avhCbZd4L68LvYT6l1kpdEnQXrF8w==
+  dependencies:
+    "@types/node" "*"
+    tapable "^2.2.0"
+    webpack "^5"
+
 "@types/ws@^8.5.1":
  version "8.5.3"
  resolved "https://registry.yarnpkg.com/@types/ws/-/ws-8.5.3.tgz#7d25a1ffbecd3c4f2d35068d0b283c037003274d"
@ -17499,7 +17508,7 @@ webpack@4:
    watchpack "^1.7.4"
    webpack-sources "^1.4.1"

-webpack@^5.64.4, webpack@^5.70.0, webpack@^5.72.0, webpack@^5.9.0:
+webpack@^5, webpack@^5.64.4, webpack@^5.70.0, webpack@^5.72.0, webpack@^5.9.0:
  version "5.72.0"
  resolved "https://registry.yarnpkg.com/webpack/-/webpack-5.72.0.tgz#f8bc40d9c6bb489a4b7a8a685101d6022b8b6e28"
  integrity sha512-qmSmbspI0Qo5ld49htys8GY9XhS9CGqFoHTsOVAnjBdg0Zn79y135R+k4IR4rKK6+eKaabMhJwiVB7xw0SJu5w==