property test framework installed but not used; describe(means) section of unit tests filled out

packages/squiggle-lang/README.md

@@ -13,6 +13,9 @@ Other:
 yarn start  # listens to files and recompiles at every mutation
 yarn test
 yarn test:watch  # keeps an active session and runs all tests at every mutation
+
+# where o := open in osx and o := xdg-open in linux,  
+yarn coverage; o _coverage/index.html  # produces coverage report and opens it in browser
 ```
 
 # TODO: clean up this README.md 

packages/squiggle-lang/__tests__/Distributions/DistributionOperation__Test.res

@@ -1,14 +1,18 @@
 open Jest
 open Expect
+open FastCheck
+// open Arbitrary
+open Property.Sync
 
 let env: DistributionOperation.env = {
   sampleCount: 100,
   xyPointLength: 100,
 }
 
-let normalDist5: GenericDist_Types.genericDist = Symbolic(#Normal({mean: 5.0, stdev: 2.0}))
-let normalDist10: GenericDist_Types.genericDist = Symbolic(#Normal({mean: 10.0, stdev: 2.0}))
-let normalDist20: GenericDist_Types.genericDist = Symbolic(#Normal({mean: 20.0, stdev: 2.0}))
+let mkNormal = (mean, stdev) => GenericDist_Types.Symbolic(#Normal({mean: mean, stdev: stdev}))
+let normalDist5: GenericDist_Types.genericDist = mkNormal(5.0, 2.0)
+let normalDist10: GenericDist_Types.genericDist = mkNormal(10.0, 2.0)
+let normalDist20: GenericDist_Types.genericDist = mkNormal(20.0, 2.0)
 let uniformDist: GenericDist_Types.genericDist = Symbolic(#Uniform({low: 9.0, high: 10.0}))
 
 let {toFloat, toDist, toString, toError} = module(DistributionOperation.Output)
@@ -19,18 +23,99 @@ let outputMap = fmap(~env)
 let toExt: option<'a> => 'a = E.O.toExt(
   "Should be impossible to reach (This error is in test file)",
 )
+let unpackFloat = x => x -> toFloat -> toExt
 
 describe("normalize", () => {
   test("has no impact on normal dist", () => {
     let result = run(FromDist(ToDist(Normalize), normalDist5))
     expect(result)->toEqual(Dist(normalDist5))
   })
+
+  // Test is vapid while I figure out how to get jest to work with fast-check
+  // monitor situation here maybe https://github.com/TheSpyder/rescript-fast-check/issues/8 ? 
+  test("all normals are already normalized", () => {
+    expect(assert_(
+      property2(
+        Arbitrary.double(()), 
+        Arbitrary.double(()), 
+        (mean, stdev) => { 
+          // open! Expect.Operators
+          open GenericDist_Types.Operation
+          run(FromDist(ToDist(Normalize), mkNormal(mean, stdev))) == DistributionOperation.Dist(mkNormal(mean, stdev))
+        }
+      )
+    )) -> toEqual(())
+  }) 
 })
 
 describe("mean", () => {
-  test("for a normal distribution", () => {
-    let result = DistributionOperation.run(~env, FromDist(ToFloat(#Mean), normalDist5))
-    expect(result)->toEqual(Float(5.0))
+  test("of a normal distribution", () => {  // should be property
+    run(FromDist(ToFloat(#Mean), normalDist5)) -> unpackFloat -> expect -> toBeCloseTo(5.0)
+  })
+
+  test("of an exponential distribution at a small rate", () => {  // should be property 
+    let rate = 1e-7  
+    let theMean = run(FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Exponential({rate: rate}))))
+    theMean -> unpackFloat -> expect -> toBeCloseTo(1.0 /. rate)  // https://en.wikipedia.org/wiki/Exponential_distribution#Mean,_variance,_moments,_and_median
+  })
+
+  test("of an exponential distribution at a larger rate", () => {
+    let rate = 10.0  
+    let theMean = run(FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Exponential({rate: rate}))))
+    theMean -> unpackFloat -> expect -> toBeCloseTo(1.0 /. rate)  // https://en.wikipedia.org/wiki/Exponential_distribution#Mean,_variance,_moments,_and_median
+  })
+
+//  test("of a cauchy distribution", () => {
+//    let result = run(FromDist(ToFloat(#Mean), GenericDist_Types.Symbolic(#Cauchy({local: 1.0, scale: 1.0}))))
+//    expect(result) -> toEqual(Error("Cauchy distributions may have no mean value."))
+//  })
+
+  test("of a triangular distribution", () => {  // should be property
+    let theMean = run(FromDist(
+      ToFloat(#Mean), 
+      GenericDist_Types.Symbolic(#Triangular({low: - 5.0, medium: 1e-3, high: 10.0}))
+    ))
+    theMean -> unpackFloat -> expect -> toBeCloseTo((-5.0 +. 1e-3 +. 10.0) /. 3.0)  // https://www.statology.org/triangular-distribution/
+  })
+
+  test("of a beta distribution with alpha much smaller than beta", () => {  // should be property
+    let theMean = run(FromDist(
+      ToFloat(#Mean), 
+      GenericDist_Types.Symbolic(#Beta({alpha: 2e-4, beta: 64.0}))
+    ))
+    theMean -> unpackFloat -> expect -> toBeCloseTo(1.0 /. (1.0 +. (64.0 /. 2e-4)))  // https://en.wikipedia.org/wiki/Beta_distribution#Mean
+  })
+
+  test("of a beta distribution with alpha much larger than beta", () => {  // should be property
+    let theMean = run(FromDist(
+      ToFloat(#Mean), 
+      GenericDist_Types.Symbolic(#Beta({alpha: 128.0, beta: 1.0}))
+    ))
+    theMean -> unpackFloat -> expect -> toBeCloseTo(1.0 /. (1.0 +. (1.0 /. 128.0)))  // https://en.wikipedia.org/wiki/Beta_distribution#Mean
+  })
+
+  test("of a lognormal", () => {  // should be property
+    let theMean = run(FromDist(
+      ToFloat(#Mean), 
+      GenericDist_Types.Symbolic(#Lognormal({mu: 2.0, sigma: 4.0}))
+    ))
+    theMean -> unpackFloat -> expect -> toBeCloseTo(Js.Math.exp(2.0 +. 4.0 ** 2.0 /. 2.0 ))  // https://brilliant.org/wiki/log-normal-distribution/
+  })
+
+  test("of a uniform", () => {
+    let theMean = run(FromDist(
+      ToFloat(#Mean), 
+      GenericDist_Types.Symbolic(#Uniform({low: 1e-5, high: 12.345}))
+    ))
+    theMean -> unpackFloat -> expect -> toBeCloseTo((1e-5 +. 12.345) /. 2.0)  // https://en.wikipedia.org/wiki/Continuous_uniform_distribution#Moments
+  })
+
+  test("of a float", () => {
+    let theMean = run(FromDist(
+      ToFloat(#Mean), 
+      GenericDist_Types.Symbolic(#Float(7.7))
+    ))
+    theMean -> unpackFloat -> expect -> toBeCloseTo(7.7)
   })
 })
 

packages/squiggle-lang/bsconfig.json

@@ -30,6 +30,9 @@
     "rationale", 
     "bisect_ppx"
   ],
+  "bs-dev-dependencies": [
+    "rescript-fast-check"
+  ],
   "gentypeconfig": {
     "language": "typescript",
     "module": "commonjs",

packages/squiggle-lang/package.json

@@ -35,6 +35,7 @@
     "docsify": "^4.12.2",
     "gentype": "^4.3.0",
     "jest": "^27.5.1",
+    "rescript-fast-check": "^1.1.1", 
     "moduleserve": "0.9.1",
     "ts-jest": "^27.1.4",
     "ts-loader": "^9.2.8",

packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res

@@ -55,7 +55,7 @@ module Exponential = {
             rate: rate,
           }),
         )
-      : Error("Exponential distributions mean must be larger than 0")
+      : Error("Exponential distributions rate must be larger than 0.")
   let pdf = (x, t: t) => Jstat.Exponential.pdf(x, t.rate)
   let cdf = (x, t: t) => Jstat.Exponential.cdf(x, t.rate)
   let inv = (p, t: t) => Jstat.Exponential.inv(p, t.rate)
@@ -71,7 +71,7 @@ module Cauchy = {
   let cdf = (x, t: t) => Jstat.Cauchy.cdf(x, t.local, t.scale)
   let inv = (p, t: t) => Jstat.Cauchy.inv(p, t.local, t.scale)
   let sample = (t: t) => Jstat.Cauchy.sample(t.local, t.scale)
-  let mean = (_: t) => Error("Cauchy distributions have no mean value.")
+  let mean = (_: t) => Error("Cauchy distributions may have no mean value.")
   let toString = ({local, scale}: t) => j`Cauchy($local, $scale)`
 }
 
@@ -80,8 +80,8 @@ module Triangular = {
   let make = (low, medium, high): result<symbolicDist, string> =>
     low < medium && medium < high
       ? Ok(#Triangular({low: low, medium: medium, high: high}))
-      : Error("Triangular values must be increasing order")
-  let pdf = (x, t: t) => Jstat.Triangular.pdf(x, t.low, t.high, t.medium)
+      : Error("Triangular values must be increasing order.")
+  let pdf = (x, t: t) => Jstat.Triangular.pdf(x, t.low, t.high, t.medium) // not obvious in jstat docs that high comes before medium? 
   let cdf = (x, t: t) => Jstat.Triangular.cdf(x, t.low, t.high, t.medium)
   let inv = (p, t: t) => Jstat.Triangular.inv(p, t.low, t.high, t.medium)
   let sample = (t: t) => Jstat.Triangular.sample(t.low, t.high, t.medium)

yarn.lock

@@ -8392,6 +8392,13 @@ extglob@^2.0.4:
     snapdragon "^0.8.1"
     to-regex "^3.0.1"
 
+fast-check@^2.17.0:
+  version "2.24.0"
+  resolved "https://registry.yarnpkg.com/fast-check/-/fast-check-2.24.0.tgz#39f85586862108a4de6394c5196ebcf8b76b6c8b"
+  integrity sha512-iNXbN90lbabaCUfnW5jyXYPwMJLFYl09eJDkXA9ZoidFlBK63gNRvcKxv+8D1OJ1kIYjwBef4bO/K3qesUeWLQ==
+  dependencies:
+    pure-rand "^5.0.1"
+
 fast-deep-equal@^3.1.1, fast-deep-equal@^3.1.3, fast-deep-equal@~3.1.3:
   version "3.1.3"
   resolved "https://registry.npmjs.org/fast-deep-equal/-/fast-deep-equal-3.1.3.tgz"
@@ -13524,6 +13531,11 @@ pure-color@^1.2.0:
   resolved "https://registry.yarnpkg.com/pure-color/-/pure-color-1.3.0.tgz#1fe064fb0ac851f0de61320a8bf796836422f33e"
   integrity sha1-H+Bk+wrIUfDeYTIKi/eWg2Qi8z4=
 
+pure-rand@^5.0.1:
+  version "5.0.1"
+  resolved "https://registry.yarnpkg.com/pure-rand/-/pure-rand-5.0.1.tgz#97a287b4b4960b2a3448c0932bf28f2405cac51d"
+  integrity sha512-ksWccjmXOHU2gJBnH0cK1lSYdvSZ0zLoCMSz/nTGh6hDvCSgcRxDyIcOBD6KNxFz3xhMPm/T267Tbe2JRymKEQ==
+
 q@^1.1.2:
   version "1.5.1"
   resolved "https://registry.yarnpkg.com/q/-/q-1.5.1.tgz#7e32f75b41381291d04611f1bf14109ac00651d7"
@@ -14712,6 +14724,13 @@ requires-port@^1.0.0:
   resolved "https://registry.yarnpkg.com/requires-port/-/requires-port-1.0.0.tgz#925d2601d39ac485e091cf0da5c6e694dc3dcaff"
   integrity sha1-kl0mAdOaxIXgkc8NpcbmlNw9yv8=
 
+rescript-fast-check@^1.1.1:
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/rescript-fast-check/-/rescript-fast-check-1.1.1.tgz#ef153cb01254b2f01a738faf85b73327d423d5e1"
+  integrity sha512-wxeW0TsL/prkRvEYGbhEiLaLKmYJaECyDcKEWh65hDqP2i76lARzVW3QmYujSYK4OnjAC70dln3X6UC/2m2Huw==
+  dependencies:
+    fast-check "^2.17.0"
+
 rescript@^9.1.4:
   version "9.1.4"
   resolved "https://registry.npmjs.org/rescript/-/rescript-9.1.4.tgz"