diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 000d73ec..9c9c86c3 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -9,3 +9,5 @@ updates:
     directory: "/" # Location of package manifests
     schedule:
       interval: "daily"
+    commit-message:
+      prefix: "⬆️"
diff --git a/packages/squiggle-lang/__tests__/JS__Test.ts b/packages/squiggle-lang/__tests__/TS/JS_test.ts
similarity index 98%
rename from packages/squiggle-lang/__tests__/JS__Test.ts
rename to packages/squiggle-lang/__tests__/TS/JS_test.ts
index 72f68ba4..8e6db265 100644
--- a/packages/squiggle-lang/__tests__/JS__Test.ts
+++ b/packages/squiggle-lang/__tests__/TS/JS_test.ts
@@ -4,7 +4,7 @@ import {
   resultMap,
   squiggleExpression,
   errorValueToString,
-} from "../src/js/index";
+} from "../../src/js/index";
 
 let testRun = (x: string): squiggleExpression => {
   let result = run(x, { sampleCount: 100, xyPointLength: 100 });
diff --git a/packages/squiggle-lang/__tests__/TS/Jstat_test.ts b/packages/squiggle-lang/__tests__/TS/Jstat_test.ts
new file mode 100644
index 00000000..d4522ec2
--- /dev/null
+++ b/packages/squiggle-lang/__tests__/TS/Jstat_test.ts
@@ -0,0 +1,58 @@
+import {
+  run,
+  Distribution,
+  squiggleExpression,
+  errorValueToString,
+  errorValue,
+  result,
+} from "../../src/js/index";
+import * as fc from "fast-check";
+
+let testRun = (x: string): any => {
+  //result<squiggleExpression, errorValue> => {
+  return run(x, { sampleCount: 1000, xyPointLength: 100 });
+};
+
+let failDefault = () => expect("codepath should never").toBe("be reached");
+
+describe("Jstat: cumulative density function", () => {
+  test("of a normal distribution at 3 stdevs to the right of the mean is within epsilon of 1", () => {
+    fc.assert(
+      fc.property(fc.float(), fc.float({ min: 1e-7 }), (mean, stdev) => {
+        let squiggleString = `cdf(normal(${mean}, ${stdev}), ${
+          mean + 3 * stdev
+        })`;
+        let squiggleResult = testRun(squiggleString);
+        let epsilon = 5e-3;
+        switch (squiggleResult.tag) {
+          case "Error":
+            expect(errorValueToString(squiggleResult.value)).toEqual(
+              "<Test cases don't seem to be finding this>"
+            );
+          case "Ok":
+            expect(squiggleResult.value.value).toBeGreaterThan(1 - epsilon);
+        }
+      })
+    );
+  });
+
+  test("of a normal distribution at 3 stdevs to the left of the mean is within epsilon of 0", () => {
+    fc.assert(
+      fc.property(fc.float(), fc.float({ min: 1e-7 }), (mean, stdev) => {
+        let squiggleString = `cdf(normal(${mean}, ${stdev}), ${
+          mean - 3 * stdev
+        })`;
+        let squiggleResult = testRun(squiggleString);
+        let epsilon = 5e-3;
+        switch (squiggleResult.tag) {
+          case "Error":
+            expect(errorValueToString(squiggleResult.value)).toEqual(
+              "<Test cases don't seem to be finding this>"
+            );
+          case "Ok":
+            expect(squiggleResult.value.value).toBeLessThan(epsilon);
+        }
+      })
+    );
+  });
+});
diff --git a/packages/squiggle-lang/__tests__/TS/Parser_test.ts b/packages/squiggle-lang/__tests__/TS/Parser_test.ts
new file mode 100644
index 00000000..d6579c49
--- /dev/null
+++ b/packages/squiggle-lang/__tests__/TS/Parser_test.ts
@@ -0,0 +1,58 @@
+import {
+  run,
+  squiggleExpression,
+  errorValue,
+  result,
+} from "../../src/js/index";
+import * as fc from "fast-check";
+
+let testRun = (x: string): result<squiggleExpression, errorValue> => {
+  return run(x, { sampleCount: 1000, xyPointLength: 100 });
+};
+
+describe("Squiggle is whitespace insensitive", () => {
+  test("when assigning a distribution to a name and calling that name", () => {
+    /*
+     * intersperse varying amounts of whitespace in a squiggle string
+     */
+    let squiggleString = (
+      a: string,
+      b: string,
+      c: string,
+      d: string,
+      e: string,
+      f: string,
+      g: string,
+      h: string
+    ): string => {
+      return `theDist${a}=${b}beta(${c}4${d},${e}5e1)${f};${g}theDist${h}`;
+    };
+    let squiggleOutput = testRun(
+      squiggleString("", "", "", "", "", "", "", "")
+    );
+    /*
+     * Add "\n" to this when multiline is introduced.
+     */
+    let whitespaceGen = () => {
+      return fc.constantFrom("", " ", "\t", "  ", "   ", "    ", "     ");
+    };
+
+    fc.assert(
+      fc.property(
+        whitespaceGen(),
+        whitespaceGen(),
+        whitespaceGen(),
+        whitespaceGen(),
+        whitespaceGen(),
+        whitespaceGen(),
+        whitespaceGen(),
+        whitespaceGen(),
+        (a, b, c, d, e, f, g, h) => {
+          expect(testRun(squiggleString(a, b, c, d, e, f, g, h))).toEqual(
+            squiggleOutput
+          );
+        }
+      )
+    );
+  });
+});
diff --git a/packages/squiggle-lang/__tests__/TS/SampleSet_test.ts b/packages/squiggle-lang/__tests__/TS/SampleSet_test.ts
new file mode 100644
index 00000000..e21d760e
--- /dev/null
+++ b/packages/squiggle-lang/__tests__/TS/SampleSet_test.ts
@@ -0,0 +1,238 @@
+import {
+  run,
+  Distribution,
+  squiggleExpression,
+  errorValueToString,
+  errorValue,
+  result,
+} from "../../src/js/index";
+import * as fc from "fast-check";
+
+let testRun = (x: string): result<squiggleExpression, errorValue> => {
+  return run(x, { sampleCount: 1000, xyPointLength: 100 });
+};
+
+let failDefault = () => expect("codepath should never").toBe("be reached");
+
+// Beware: float64Array makes it appear in an infinite loop.
+let arrayGen = () =>
+  fc.float32Array({
+    minLength: 10,
+    maxLength: 10000,
+    noDefaultInfinity: true,
+    noNaN: true,
+  });
+
+describe("SampleSet: cdf", () => {
+  let n = 10000
+  test("at the highest number in the distribution is within epsilon of 1", () => {
+    fc.assert(
+      fc.property(arrayGen(), (xs) => {
+        let ys = Array.from(xs);
+        let max = Math.max(...ys);
+        // Should compute with squiglge strings once interpreter has `sample`
+        let dist = new Distribution(
+          { tag: "SampleSet", value: ys },
+          { sampleCount: n, xyPointLength: 100 }
+        );
+        let cdfValue = dist.cdf(max).value
+        let min = Math.min(...ys)
+        let epsilon = 5e-3;
+          if (max - min < epsilon) {
+              expect(cdfValue).toBeLessThan(1 - epsilon)
+          } else {
+              expect(dist.cdf(max).value).toBeGreaterThan(1 - epsilon);
+          }
+      })
+    );
+  });
+
+  test("at the lowest number in the distribution is within epsilon of 0", () => {
+    fc.assert(
+      fc.property(arrayGen(), (xs) => {
+        let ys = Array.from(xs);
+        let min = Math.min(...ys);
+        // Should compute with squiggle strings once interpreter has `sample`
+        let dist = new Distribution(
+          { tag: "SampleSet", value: ys },
+          { sampleCount: n, xyPointLength: 100 }
+        );
+        let cdfValue = dist.cdf(min).value
+        let max = Math.max(...ys);
+        let epsilon = 5e-3;
+          if (max - min < epsilon) {
+              expect(cdfValue).toBeGreaterThan(epsilon)
+          } else {
+              expect(cdfValue).toBeLessThan(epsilon);
+          }
+      })
+    );
+  });
+
+  test("is <= 1 everywhere with equality when x is higher than the max", () => {
+    fc.assert(
+      fc.property(arrayGen(), fc.float(), (xs, x) => {
+        let ys = Array.from(xs)
+        let dist = new Distribution(
+          { tag: "SampleSet", value: ys },
+          { sampleCount: n, xyPointLength: 100 }
+        );
+        let cdfValue = dist.cdf(x).value
+        let epsilon = 1e-1
+        if (x > Math.max(...ys)) {   // The really good way to do this is to have epsilon be a function of the percentage by which x > max(ys)
+          expect(cdfValue).toBeGreaterThan(1 - epsilon - epsilon ** 2)
+        } else {
+          expect(cdfValue).toBeLessThan(1);
+        }
+      })
+    );
+  });
+
+  test("is >= 0 everywhere with equality when x is lower than the min", () => {
+    fc.assert(
+      fc.property(arrayGen(), fc.float(), (xs, x) => {
+          let ys = Array.from(xs)
+        let dist = new Distribution(
+          { tag: "SampleSet", value: ys },
+          { sampleCount: n, xyPointLength: 100 }
+        );
+          let cdfValue = dist.cdf(x).value
+          if (x < Math.min(...ys)) {
+              expect(cdfValue).toEqual(0)
+          } else {
+              expect(cdfValue).toBeGreaterThan(0);
+          }
+      })
+    );
+  });
+});
+
+describe("SampleSet: pdf of extremes is lower than pdf of mean.", () => {
+  let n = 1000
+
+  test("a sampleset distribution's pdf assigns less weight to the max than to the mean", () => {
+    fc.assert(
+      fc.property(arrayGen(), (xs) => {
+        let ys = Array.from(xs);
+        let max = Math.max(...ys);
+        let mean = ys.reduce((a, b) => a + b, 0.0) / ys.length;
+        // Should be from squiggleString once interpreter exposes sampleset
+        let dist = new Distribution(
+          { tag: "SampleSet", value: ys },
+          { sampleCount: n, xyPointLength: 100 }
+        );
+        let pdfMean = dist.pdf(mean);
+        let pdfMax = dist.pdf(max);
+        switch (pdfMax.tag) {
+          case "Ok":
+            let min = Math.min(...ys)
+            switch (pdfMean.tag) {
+              case "Ok":
+                if (max == min) {
+                  expect(pdfMax.value).toBeLessThanOrEqual(pdfMean.value);
+                } else {
+                  expect(pdfMax.value).toBeLessThan(pdfMean.value);
+                }
+              case "Error":
+                if (max == min) {
+                  expect(pdfMean.value).toEqual(1);
+                } else {
+                  expect(pdfMean.value).toEqual("error message");
+                }
+              default:
+                failDefault();
+            }
+          case "Error":
+            switch (pdfMean.tag) {
+              case "Ok":
+                expect(pdfMax.value).toEqual("error message");
+              case "Error":
+                expect(pdfMax.value).toEqual(pdfMean.value);
+              default:
+                failDefault();
+            }
+          default:
+            failDefault();
+        }
+      })
+    );
+  });
+});
+
+// describe("SampleSet: mean is mean", () => {
+//  test("mean(samples(xs)) sampling twice as widely as the input", () => {
+//    fc.assert(
+//      fc.property(
+//        fc.float64Array({ minLength: 10, maxLength: 100000 }),
+//        (xs) => {
+//          let ys = Array.from(xs);
+//          let n = ys.length;
+//          let dist = new Distribution(
+//            { tag: "SampleSet", value: ys },
+//            { sampleCount: 2 * n, xyPointLength: 4 * n }
+//          );
+//
+//          expect(dist.mean().value).toBeCloseTo(
+//            ys.reduce((a, b) => a + b, 0.0) / n
+//          );
+//        }
+//      )
+//    );
+//  });
+//
+//  test("mean(samples(xs)) sampling half as widely as the input", () => {
+//    fc.assert(
+//      fc.property(
+//        fc.float64Array({ minLength: 10, maxLength: 100000 }),
+//        (xs) => {
+//          let ys = Array.from(xs);
+//          let n = ys.length;
+//          let dist = new Distribution(
+//            { tag: "SampleSet", value: ys },
+//            { sampleCount: Math.floor(5 / 2), xyPointLength: 4 * n }
+//          );
+//
+//          expect(dist.mean().value).toBeCloseTo(
+//            ys.reduce((a, b) => a + b, 0.0) / n
+//          );
+//        }
+//      )
+//    );
+//  });
+// });
+
+// describe("Mean of mixture is weighted average of means", () => {
+//  test("mx(beta(a,b), lognormal(m,s), [x,y])", () => {
+//    fc.assert(
+//      fc.property(
+//        fc.float({ min: 1e-1 }),  // alpha
+//        fc.float({ min: 1 }),   // beta
+//        fc.float(),  // mu
+//        fc.float({ min: 1e-1 }),  // sigma
+//        fc.float({ min: 1e-7 }),
+//        fc.float({ min: 1e-7 }),
+//        (a, b, m, s, x, y) => {
+//          let squiggleString = `mean(mx(beta(${a},${b}), lognormal(${m},${s}), [${x}, ${y}]))`;
+//          let res = testRun(squiggleString);
+//          switch (res.tag) {
+//            case "Error":
+//              expect(errorValueToString(res.value)).toEqual(
+//                "<I wonder if test cases will find this>"
+//              );
+//            case "Ok":
+//              let betaWeight = x / (x + y);
+//              let lognormalWeight = y / (x + y);
+//              let betaMean = 1 / (1 + b / a);
+//              let lognormalMean = m + s ** 2 / 2;
+//              expect(res.value).toEqual({
+//                tag: "number",
+//                value: betaWeight * betaMean + lognormalWeight * lognormalMean,
+//              });
+//            default:
+//              expect("mean returned").toBe(`something other than a number`);
+//          }
+//        }
+//      )
+//    );
+//  });
+// });
diff --git a/packages/squiggle-lang/__tests__/TS/Scalars_test.ts b/packages/squiggle-lang/__tests__/TS/Scalars_test.ts
new file mode 100644
index 00000000..401ac32a
--- /dev/null
+++ b/packages/squiggle-lang/__tests__/TS/Scalars_test.ts
@@ -0,0 +1,62 @@
+import {
+  run,
+  Distribution,
+  resultMap,
+  squiggleExpression,
+  errorValueToString,
+  errorValue,
+  result,
+} from "../../src/js/index";
+import * as fc from "fast-check";
+
+let testRun = (x: string): result<squiggleExpression, errorValue> => {
+  return run(x, { sampleCount: 100, xyPointLength: 100 });
+};
+
+describe("Scalar manipulation is well-modeled by javascript math", () => {
+  test("in the case of logarithms (with assignment)", () => {
+    fc.assert(
+      fc.property(fc.float(), (x) => {
+        let squiggleString = `x = log(${x}); x`;
+        let squiggleResult = testRun(squiggleString);
+        if (x == 0) {
+          expect(squiggleResult.value).toEqual({
+            tag: "number",
+            value: -Infinity,
+          });
+        } else if (x < 0) {
+          expect(squiggleResult.value).toEqual({
+            tag: "RETodo",
+            value:
+              "somemessage (confused why a test case hasn't pointed out to me that this message is bogus)",
+          });
+        } else {
+          expect(squiggleResult.value).toEqual({
+            tag: "number",
+            value: Math.log(x),
+          });
+        }
+      })
+    );
+  });
+
+  test("in the case of addition (with assignment)", () => {
+    fc.assert(
+      fc.property(fc.float(), fc.float(), fc.float(), (x, y, z) => {
+        let squiggleString = `x = ${x}; y = ${y}; z = ${z}; x + y + z`;
+        let squiggleResult = testRun(squiggleString);
+        switch (squiggleResult.tag) {
+          case "Error":
+            expect(errorValueToString(squiggleResult.value)).toEqual(
+              "some message (hopefully a test case points it out to me)"
+            );
+          case "Ok":
+            expect(squiggleResult.value).toEqual({
+              tag: "number",
+              value: x + y + z,
+            });
+        }
+      })
+    );
+  });
+});
diff --git a/packages/squiggle-lang/__tests__/TS/Symbolic_test.ts b/packages/squiggle-lang/__tests__/TS/Symbolic_test.ts
new file mode 100644
index 00000000..f97adbec
--- /dev/null
+++ b/packages/squiggle-lang/__tests__/TS/Symbolic_test.ts
@@ -0,0 +1,44 @@
+import {
+  run,
+  squiggleExpression,
+  errorValueToString,
+  errorValue,
+  result,
+} from "../../src/js/index";
+import * as fc from "fast-check";
+
+let testRun = (x: string): result<squiggleExpression, errorValue> => {
+  return run(x, { sampleCount: 100, xyPointLength: 100 });
+};
+
+describe("Symbolic mean", () => {
+  let triangularInputError = {
+    tag: "Error",
+    value: {
+      tag: "RETodo",
+      value: "Triangular values must be increasing order.",
+    },
+  };
+  test("mean(triangular(x,y,z))", () => {
+    fc.assert(
+      fc.property(fc.float(), fc.float(), fc.float(), (x, y, z) => {
+        let res = testRun(`mean(triangular(${x},${y},${z}))`);
+        if (!(x < y && y < z)) {
+          expect(res).toEqual(triangularInputError);
+        } else {
+          switch (res.tag) {
+            case "Error":
+              expect(errorValueToString(res.value)).toEqual(
+                "<Test cases don't seem to be finding this>"
+              );
+            case "Ok":
+              expect(res.value).toEqual({
+                tag: "number",
+                value: (x + y + z) / 3,
+              });
+          }
+        }
+      })
+    );
+  });
+});
diff --git a/packages/squiggle-lang/package.json b/packages/squiggle-lang/package.json
index fa551fae..efec7810 100644
--- a/packages/squiggle-lang/package.json
+++ b/packages/squiggle-lang/package.json
@@ -44,6 +44,7 @@
     "moduleserve": "0.9.1",
     "ts-jest": "^27.1.4",
     "ts-loader": "^9.2.8",
+    "fast-check": "2.24.0",
     "typescript": "^4.6.3",
     "webpack": "^5.72.0",
     "webpack-cli": "^4.9.2"
diff --git a/yarn.lock b/yarn.lock
index 1bd0a6cc..8f6746b1 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -8417,6 +8417,13 @@ extglob@^2.0.4:
     snapdragon "^0.8.1"
     to-regex "^3.0.1"
 
+fast-check@2.24.0:
+  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.yarnpkg.com/fast-deep-equal/-/fast-deep-equal-3.1.3.tgz#3a7d56b559d6cbc3eb512325244e619a65c6c525"
@@ -13573,6 +13580,11 @@ 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"