Merge remote-tracking branch 'origin/develop' into log-score-attempt

2022-05-03 10:17:17 -04:00 · 2022-05-03 10:17:17 -04:00 · 6c815a62ff
commit 6c815a62ff
parent 5d6de7b487 6112487b78
40 changed files with 1360 additions and 614 deletions
--- a/packages/components/src/components/SquiggleChart.tsx
+++ b/packages/components/src/components/SquiggleChart.tsx
@ -141,6 +141,8 @@ const SquiggleItem: React.FC<SquiggleItemProps> = ({
              expression={r}
              width={width !== undefined ? width - 20 : width}
              height={50}
+              showTypes={showTypes}
+              showControls={showControls}
            />
          ))}
        </VariableBox>
@ -155,11 +157,25 @@ const SquiggleItem: React.FC<SquiggleItemProps> = ({
                expression={r}
                width={width !== undefined ? width - 20 : width}
                height={50}
+                showTypes={showTypes}
+                showControls={showControls}
              />
            </>
          ))}
        </VariableBox>
      );
+    case "arraystring":
+      return (
+        <VariableBox heading="Array String" showTypes={showTypes}>
+          {expression.value.map((r) => `"${r}"`)}
+        </VariableBox>
+      );
+    case "lambda":
+      return (
+        <ErrorBox heading="No Viewer">
+          There is no viewer currently available for function types.
+        </ErrorBox>
+      );
  }
 };

--- a/packages/squiggle-lang/tests/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros_test.res
@ -0,0 +1,142 @@
+open Jest
+// open Expect
+
+open Reducer_Expression_ExpressionBuilder
+open Reducer_TestMacroHelpers
+module ExpressionT = Reducer_Expression_T
+
+let exampleExpression = eNumber(1.)
+let exampleExpressionY = eSymbol("y")
+let exampleStatementY = eLetStatement("y", eNumber(1.))
+let exampleStatementX = eLetStatement("y", eSymbol("x"))
+let exampleStatementZ = eLetStatement("z", eSymbol("y"))
+
+// If it is not a macro then it is not expanded
+testMacro([], exampleExpression, "Ok(1)")
+
+describe("bindStatement", () => {
+  // A statement is bound by the bindings created by the previous statement
+  testMacro([], eBindStatement(eBindings([]), exampleStatementY), "Ok((:$setBindings {} :y 1))")
+  // Then it answers the bindings for the next statement when reduced
+  testMacroEval([], eBindStatement(eBindings([]), exampleStatementY), "Ok({y: 1})")
+  // Now let's feed a binding to see what happens
+  testMacro(
+    [],
+    eBindStatement(eBindings([("x", EvNumber(2.))]), exampleStatementX),
+    "Ok((:$setBindings {x: 2} :y 2))",
+  )
+  // An expression does not return a binding, thus error
+  testMacro([], eBindStatement(eBindings([]), exampleExpression), "Error(Assignment expected)")
+  // When bindings from previous statement are missing the context is injected. This must be the first statement of a block
+  testMacro(
+    [("z", EvNumber(99.))],
+    eBindStatementDefault(exampleStatementY),
+    "Ok((:$setBindings {z: 99} :y 1))",
+  )
+})
+
+describe("bindExpression", () => {
+  // x is simply bound in the expression
+  testMacro([], eBindExpression(eBindings([("x", EvNumber(2.))]), eSymbol("x")), "Ok(2)")
+  // When an let statement is the end expression then bindings are returned
+  testMacro(
+    [],
+    eBindExpression(eBindings([("x", EvNumber(2.))]), exampleStatementY),
+    "Ok((:$exportBindings (:$setBindings {x: 2} :y 1)))",
+  )
+  // Now let's reduce that expression
+  testMacroEval(
+    [],
+    eBindExpression(eBindings([("x", EvNumber(2.))]), exampleStatementY),
+    "Ok({x: 2,y: 1})",
+  )
+  // When bindings are missing the context is injected. This must be the first and last statement of a block
+  testMacroEval(
+    [("z", EvNumber(99.))],
+    eBindExpressionDefault(exampleStatementY),
+    "Ok({y: 1,z: 99})",
+  )
+})
+
+describe("block", () => {
+  // Block with a single expression
+  testMacro([], eBlock(list{exampleExpression}), "Ok((:$$bindExpression 1))")
+  testMacroEval([], eBlock(list{exampleExpression}), "Ok(1)")
+  // Block with a single statement
+  testMacro([], eBlock(list{exampleStatementY}), "Ok((:$$bindExpression (:$let :y 1)))")
+  testMacroEval([], eBlock(list{exampleStatementY}), "Ok({y: 1})")
+  // Block with a statement and an expression
+  testMacro(
+    [],
+    eBlock(list{exampleStatementY, exampleExpressionY}),
+    "Ok((:$$bindExpression (:$$bindStatement (:$let :y 1)) :y))",
+  )
+  testMacroEval([], eBlock(list{exampleStatementY, exampleExpressionY}), "Ok(1)")
+  // Block with a statement and another statement
+  testMacro(
+    [],
+    eBlock(list{exampleStatementY, exampleStatementZ}),
+    "Ok((:$$bindExpression (:$$bindStatement (:$let :y 1)) (:$let :z :y)))",
+  )
+  testMacroEval([], eBlock(list{exampleStatementY, exampleStatementZ}), "Ok({y: 1,z: 1})")
+  // Block inside a block
+  testMacro(
+    [],
+    eBlock(list{eBlock(list{exampleExpression})}),
+    "Ok((:$$bindExpression (:$$block 1)))",
+  )
+  testMacroEval([], eBlock(list{eBlock(list{exampleExpression})}), "Ok(1)")
+  // Block assigned to a variable
+  testMacro(
+    [],
+    eBlock(list{eLetStatement("z", eBlock(list{eBlock(list{exampleExpressionY})}))}),
+    "Ok((:$$bindExpression (:$let :z (:$$block (:$$block :y)))))",
+  )
+  testMacroEval(
+    [],
+    eBlock(list{eLetStatement("z", eBlock(list{eBlock(list{exampleExpressionY})}))}),
+    "Ok({z: :y})",
+  )
+  // Empty block
+  testMacro([], eBlock(list{}), "Ok(:undefined block)") //TODO: should be an error
+  //   :$$block (:$$block (:$let :y (:add :x 1)) :y)"
+  testMacro(
+    [],
+    eBlock(list{
+      eBlock(list{
+        eLetStatement("y", eFunction("add", list{eSymbol("x"), eNumber(1.)})),
+        eSymbol("y"),
+      }),
+    }),
+    "Ok((:$$bindExpression (:$$block (:$let :y (:add :x 1)) :y)))",
+  )
+  MyOnly.testMacroEval(
+    [("x", EvNumber(1.))],
+    eBlock(list{
+      eBlock(list{
+        eLetStatement("y", eFunction("add", list{eSymbol("x"), eNumber(1.)})),
+        eSymbol("y"),
+      }),
+    }),
+    "Ok(2)",
+  )
+})
+
+describe("lambda", () => {
+  // assign a lambda to a variable
+  let lambdaExpression = eFunction("$$lambda", list{eArrayString(["y"]), exampleExpressionY})
+  testMacro([], lambdaExpression, "Ok(lambda(y=>internal))")
+  // call a lambda
+  let callLambdaExpression = list{lambdaExpression, eNumber(1.)}->ExpressionT.EList
+  testMacro([], callLambdaExpression, "Ok(((:$$lambda [y] :y) 1))")
+  testMacroEval([], callLambdaExpression, "Ok(1)")
+  // Parameters shadow the outer scope
+  testMacroEval([("y", EvNumber(666.))], callLambdaExpression, "Ok(1)")
+  // When not shadowed by the parameters, the outer scope variables are available
+  let lambdaExpression = eFunction(
+    "$$lambda",
+    list{eArrayString(["z"]), eFunction("add", list{eSymbol("y"), eSymbol("z")})},
+  )
+  let callLambdaExpression = eList(list{lambdaExpression, eNumber(1.)})
+  testMacroEval([("y", EvNumber(666.))], callLambdaExpression, "Ok(667)")
+})
--- a/packages/squiggle-lang/tests/Reducer/Reducer_Expression/Reducer_Expression_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_Expression/Reducer_Expression_test.res
@ -0,0 +1,6 @@
+open Jest
+open Expect
+
+test("dummy", () => {
+  expect(true)->toBe(true)
+})
--- a/packages/squiggle-lang/tests/Reducer/Reducer_MathJs/Reducer_MathJsEval_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_MathJs/Reducer_MathJsEval_test.res
@ -1,5 +1,5 @@
 open ReducerInterface.ExpressionValue
-module MathJs = Reducer.MathJs
+module MathJs = Reducer_MathJs
 module ErrorValue = Reducer.ErrorValue

 open Jest
--- a/packages/squiggle-lang/tests/Reducer/Reducer_MathJs/Reducer_MathJsParse_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_MathJs/Reducer_MathJsParse_test.res
@ -1,4 +1,4 @@
-module Parse = Reducer.MathJs.Parse
+module Parse = Reducer_MathJs.Parse
 module Result = Belt.Result

 open Jest
@ -18,8 +18,14 @@ module MySkip = {
    Skip.test(desc, () => expectParseToBe(expr, answer))
 }

+module MyOnly = {
+  let testParse = (expr, answer) => Only.test(expr, () => expectParseToBe(expr, answer))
+  let testDescriptionParse = (desc, expr, answer) =>
+    Only.test(desc, () => expectParseToBe(expr, answer))
+}
+
 describe("MathJs parse", () => {
-  describe("literals operators paranthesis", () => {
+  describe("literals operators parenthesis", () => {
    testParse("1", "1")
    testParse("'hello'", "'hello'")
    testParse("true", "true")
@ -40,15 +46,15 @@ describe("MathJs parse", () => {
  })

  describe("functions", () => {
-    MySkip.testParse("identity(x) = x", "???")
-    MySkip.testParse("identity(x)", "???")
+    testParse("identity(x) = x", "identity = (x) => x")
+    testParse("identity(x)", "identity(x)")
  })

  describe("arrays", () => {
    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)")
+    testParse("range(0, 4)", "range(0, 4)")
    testDescriptionParse("index", "([0,1,2])[1]", "([0, 1, 2])[1]")
  })

@ -58,11 +64,6 @@ describe("MathJs parse", () => {
  })

  describe("comments", () => {
-    MySkip.testDescriptionParse("define", "# This is a comment", "???")
-  })
-
-  describe("if statement", () => {
-    // TODO Tertiary operator instead
-    MySkip.testDescriptionParse("define", "if (true) { 1 } else { 0 }", "???")
+    testDescriptionParse("define", "1 # This is a comment", "1")
  })
 })
--- a/packages/squiggle-lang/tests/Reducer/Reducer_TestHelpers.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_TestHelpers.res
@ -1,40 +1,31 @@
-module Expression = Reducer.Expression
+module ExpressionT = Reducer_Expression_T
 module ExpressionValue = ReducerInterface.ExpressionValue
+module ErrorValue = Reducer_ErrorValue

 open Jest
 open Expect

+let unwrapRecord = rValue =>
+  rValue->Belt.Result.flatMap(value =>
+    switch value {
+    | ExpressionValue.EvRecord(aRecord) => Ok(aRecord)
+    | _ => ErrorValue.RETodo("TODO: External bindings must be returned")->Error
+    }
+  )
+
 let expectParseToBe = (expr: string, answer: string) =>
-  Reducer.parse(expr)->Expression.toStringResult->expect->toBe(answer)
-
-let expectParseOuterToBe = (expr: string, answer: string) =>
-  Reducer.parseOuter(expr)->Expression.toStringResult->expect->toBe(answer)
-
-let expectParsePartialToBe = (expr: string, answer: string) =>
-  Reducer.parsePartial(expr)->Expression.toStringResult->expect->toBe(answer)
+  Reducer.parse(expr)->ExpressionT.toStringResult->expect->toBe(answer)

 let expectEvalToBe = (expr: string, answer: string) =>
  Reducer.evaluate(expr)->ExpressionValue.toStringResult->expect->toBe(answer)

 let expectEvalBindingsToBe = (expr: string, bindings: Reducer.externalBindings, answer: string) =>
-  Reducer.evaluateUsingExternalBindings(expr, bindings)
+  Reducer.evaluateUsingOptions(expr, ~externalBindings=Some(bindings), ~environment=None)
  ->ExpressionValue.toStringResult
  ->expect
  ->toBe(answer)

-let expectEvalPartialBindingsToBe = (
-  expr: string,
-  bindings: Reducer.externalBindings,
-  answer: string,
-) =>
-  Reducer.evaluatePartialUsingExternalBindings(expr, bindings)
-  ->ExpressionValue.toStringResultRecord
-  ->expect
-  ->toBe(answer)
-
 let testParseToBe = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
-let testParseOuterToBe = (expr, answer) => test(expr, () => expectParseOuterToBe(expr, answer))
-let testParsePartialToBe = (expr, answer) => test(expr, () => expectParsePartialToBe(expr, answer))
 let testDescriptionParseToBe = (desc, expr, answer) =>
  test(desc, () => expectParseToBe(expr, answer))

@ -42,34 +33,16 @@ let testEvalToBe = (expr, answer) => test(expr, () => expectEvalToBe(expr, answe
 let testDescriptionEvalToBe = (desc, expr, answer) => test(desc, () => expectEvalToBe(expr, answer))
 let testEvalBindingsToBe = (expr, bindingsList, answer) =>
  test(expr, () => expectEvalBindingsToBe(expr, bindingsList->Js.Dict.fromList, answer))
-let testEvalPartialBindingsToBe = (expr, bindingsList, answer) =>
-  test(expr, () => expectEvalPartialBindingsToBe(expr, bindingsList->Js.Dict.fromList, answer))

 module MySkip = {
  let testParseToBe = (expr, answer) => Skip.test(expr, () => expectParseToBe(expr, answer))
-  let testParseOuterToBe = (expr, answer) =>
-    Skip.test(expr, () => expectParseOuterToBe(expr, answer))
-  let testParsePartialToBe = (expr, answer) =>
-    Skip.test(expr, () => expectParsePartialToBe(expr, answer))
  let testEvalToBe = (expr, answer) => Skip.test(expr, () => expectEvalToBe(expr, answer))
  let testEvalBindingsToBe = (expr, bindingsList, answer) =>
    Skip.test(expr, () => expectEvalBindingsToBe(expr, bindingsList->Js.Dict.fromList, answer))
-  let testEvalPartialBindingsToBe = (expr, bindingsList, answer) =>
-    Skip.test(expr, () =>
-      expectEvalPartialBindingsToBe(expr, bindingsList->Js.Dict.fromList, answer)
-    )
 }
 module MyOnly = {
  let testParseToBe = (expr, answer) => Only.test(expr, () => expectParseToBe(expr, answer))
-  let testParseOuterToBe = (expr, answer) =>
-    Only.test(expr, () => expectParseOuterToBe(expr, answer))
-  let testParsePartialToBe = (expr, answer) =>
-    Only.test(expr, () => expectParsePartialToBe(expr, answer))
  let testEvalToBe = (expr, answer) => Only.test(expr, () => expectEvalToBe(expr, answer))
  let testEvalBindingsToBe = (expr, bindingsList, answer) =>
    Only.test(expr, () => expectEvalBindingsToBe(expr, bindingsList->Js.Dict.fromList, answer))
-  let testEvalPartialBindingsToBe = (expr, bindingsList, answer) =>
-    Only.test(expr, () =>
-      expectEvalPartialBindingsToBe(expr, bindingsList->Js.Dict.fromList, answer)
-    )
 }
--- a/packages/squiggle-lang/tests/Reducer/Reducer_TestMacroHelpers.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_TestMacroHelpers.res
@ -0,0 +1,82 @@
+open Jest
+open Expect
+
+module Bindings = Reducer_Expression_Bindings
+module Expression = Reducer_Expression
+module ExpressionValue = ReducerInterface_ExpressionValue
+module ExpressionWithContext = Reducer_ExpressionWithContext
+module Macro = Reducer_Expression_Macro
+module T = Reducer_Expression_T
+
+let testMacro_ = (
+  tester,
+  bindArray: array<(string, ExpressionValue.expressionValue)>,
+  expr: T.expression,
+  expectedCode: string,
+) => {
+  let bindings = Belt.Map.String.fromArray(bindArray)
+  tester(expr->T.toString, () =>
+    expr
+    ->Macro.expandMacroCall(
+      bindings,
+      ExpressionValue.defaultEnvironment,
+      Expression.reduceExpression,
+    )
+    ->ExpressionWithContext.toStringResult
+    ->expect
+    ->toEqual(expectedCode)
+  )
+}
+
+let testMacroEval_ = (
+  tester,
+  bindArray: array<(string, ExpressionValue.expressionValue)>,
+  expr: T.expression,
+  expectedValue: string,
+) => {
+  let bindings = Belt.Map.String.fromArray(bindArray)
+  tester(expr->T.toString, () =>
+    expr
+    ->Macro.doMacroCall(bindings, ExpressionValue.defaultEnvironment, Expression.reduceExpression)
+    ->ExpressionValue.toStringResult
+    ->expect
+    ->toEqual(expectedValue)
+  )
+}
+
+let testMacro = (
+  bindArray: array<(string, ExpressionValue.expressionValue)>,
+  expr: T.expression,
+  expectedExpr: string,
+) => testMacro_(test, bindArray, expr, expectedExpr)
+let testMacroEval = (
+  bindArray: array<(string, ExpressionValue.expressionValue)>,
+  expr: T.expression,
+  expectedValue: string,
+) => testMacroEval_(test, bindArray, expr, expectedValue)
+
+module MySkip = {
+  let testMacro = (
+    bindArray: array<(string, ExpressionValue.expressionValue)>,
+    expr: T.expression,
+    expectedExpr: string,
+  ) => testMacro_(Skip.test, bindArray, expr, expectedExpr)
+  let testMacroEval = (
+    bindArray: array<(string, ExpressionValue.expressionValue)>,
+    expr: T.expression,
+    expectedValue: string,
+  ) => testMacroEval_(Skip.test, bindArray, expr, expectedValue)
+}
+
+module MyOnly = {
+  let testMacro = (
+    bindArray: array<(string, ExpressionValue.expressionValue)>,
+    expr: T.expression,
+    expectedExpr: string,
+  ) => testMacro_(Only.test, bindArray, expr, expectedExpr)
+  let testMacroEval = (
+    bindArray: array<(string, ExpressionValue.expressionValue)>,
+    expr: T.expression,
+    expectedValue: string,
+  ) => testMacroEval_(Only.test, bindArray, expr, expectedValue)
+}
--- a/packages/squiggle-lang/tests/Reducer/Reducer_debugging_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_debugging_test.res
@ -0,0 +1,16 @@
+open Jest
+open Reducer_TestHelpers
+
+/*
+    You can wrap around any expression with inspect(expr) to log the value of that expression.
+    This is useful for debugging. inspect(expr) returns the value of expr, but also prints it out.
+
+    There is a second version of inspect that takes a label, which will print out the label and the value.
+
+    inspectPerformace(expr, label) will print out the value of expr, the label, and the time it took to evaluate expr.
+*/
+describe("Debugging", () => {
+  testEvalToBe("inspect(1)", "Ok(1)")
+  testEvalToBe("inspect(1, \"one\")", "Ok(1)")
+  testEvalToBe("inspectPerformance(1, \"one\")", "Ok(1)")
+})
--- a/packages/squiggle-lang/tests/Reducer/Reducer_externalBindings_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_externalBindings_test.res
@ -1,60 +1,63 @@
+// TODO: Reimplement with usual parse
 open Jest
 open Reducer_TestHelpers

-describe("Parse for Bindings", () => {
-  testParseOuterToBe("x", "Ok((:$$bindExpression (:$$bindings) :x))")
-  testParseOuterToBe("x+1", "Ok((:$$bindExpression (:$$bindings) (:add :x 1)))")
-  testParseOuterToBe(
-    "y = x+1; y",
-    "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :y (:add :x 1))) :y))",
-  )
-})
+// describe("Parse for Bindings", () => {
+//   testParseOuterToBe("x", "Ok((:$$bindExpression (:$$bindings) :x))")
+//   testParseOuterToBe("x+1", "Ok((:$$bindExpression (:$$bindings) (:add :x 1)))")
+//   testParseOuterToBe(
+//     "y = x+1; y",
+//     "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :y (:add :x 1))) :y))",
+//   )
+// })

-describe("Parse Partial", () => {
-  testParsePartialToBe(
-    "x",
-    "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) :x) (:$exportVariablesExpression)))",
-  )
-  testParsePartialToBe(
-    "y=x",
-    "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :y :x)) (:$exportVariablesExpression)))",
-  )
-  testParsePartialToBe(
-    "y=x+1",
-    "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :y (:add :x 1))) (:$exportVariablesExpression)))",
-  )
-  testParsePartialToBe(
-    "y = x+1; z = y",
-    "Ok((:$$bindExpression (:$$bindStatement (:$$bindStatement (:$$bindings) (:$let :y (:add :x 1))) (:$let :z :y)) (:$exportVariablesExpression)))",
-  )
-})
+// describe("Parse Partial", () => {
+//   testParsePartialToBe(
+//     "x",
+//     "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) :x) (:$exportVariablesExpression)))",
+//   )
+//   testParsePartialToBe(
+//     "y=x",
+//     "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :y :x)) (:$exportVariablesExpression)))",
+//   )
+//   testParsePartialToBe(
+//     "y=x+1",
+//     "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :y (:add :x 1))) (:$exportVariablesExpression)))",
+//   )
+//   testParsePartialToBe(
+//     "y = x+1; z = y",
+//     "Ok((:$$bindExpression (:$$bindStatement (:$$bindStatement (:$$bindings) (:$let :y (:add :x 1))) (:$let :z :y)) (:$exportVariablesExpression)))",
+//   )
+// })

 describe("Eval with Bindings", () => {
  testEvalBindingsToBe("x", list{("x", ExpressionValue.EvNumber(1.))}, "Ok(1)")
  testEvalBindingsToBe("x+1", list{("x", ExpressionValue.EvNumber(1.))}, "Ok(2)")
+  testParseToBe("y = x+1; y", "Ok((:$$block (:$$block (:$let :y (:add :x 1)) :y)))")
  testEvalBindingsToBe("y = x+1; y", list{("x", ExpressionValue.EvNumber(1.))}, "Ok(2)")
+  testEvalBindingsToBe("y = x+1", list{("x", ExpressionValue.EvNumber(1.))}, "Ok({x: 1,y: 2})")
 })

 /*
    Partial code is a partial code fragment that is cut out from a larger code.
    Therefore it does not end with an expression.
 */
-describe("Eval Partial", () => {
-  testEvalPartialBindingsToBe(
-    //   A partial cannot end with an expression
-    "x",
-    list{("x", ExpressionValue.EvNumber(1.))},
-    "Error(Assignment expected)",
-  )
-  testEvalPartialBindingsToBe("y=x", list{("x", ExpressionValue.EvNumber(1.))}, "Ok({x: 1, y: 1})")
-  testEvalPartialBindingsToBe(
-    "y=x+1",
-    list{("x", ExpressionValue.EvNumber(1.))},
-    "Ok({x: 1, y: 2})",
-  )
-  testEvalPartialBindingsToBe(
-    "y = x+1; z = y",
-    list{("x", ExpressionValue.EvNumber(1.))},
-    "Ok({x: 1, y: 2, z: 2})",
-  )
-})
+// describe("Eval Partial", () => {
+//   testEvalPartialBindingsToBe(
+//     //   A partial cannot end with an expression
+//     "x",
+//     list{("x", ExpressionValue.EvNumber(1.))},
+//     "Error(Assignment expected)",
+//   )
+//   testEvalPartialBindingsToBe("y=x", list{("x", ExpressionValue.EvNumber(1.))}, "Ok({x: 1,y: 1})")
+//   testEvalPartialBindingsToBe(
+//     "y=x+1",
+//     list{("x", ExpressionValue.EvNumber(1.))},
+//     "Ok({x: 1,y: 2})",
+//   )
+//   testEvalPartialBindingsToBe(
+//     "y = x+1; z = y",
+//     list{("x", ExpressionValue.EvNumber(1.))},
+//     "Ok({x: 1,y: 2,z: 2})",
+//   )
+// })
--- a/packages/squiggle-lang/tests/Reducer/Reducer_functionAssignment_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_functionAssignment_test.res
@ -0,0 +1,12 @@
+open Jest
+open Reducer_TestHelpers
+
+describe("Parse function assignment", () => {
+  testParseToBe("f(x)=x", "Ok((:$$block (:$let :f (:$$lambda [x] (:$$block :x)))))")
+  testParseToBe("f(x)=2*x", "Ok((:$$block (:$let :f (:$$lambda [x] (:$$block (:multiply 2 :x))))))")
+  //MathJs does not allow blocks in function definitions
+})
+
+describe("Evaluate function assignment", () => {
+  testEvalToBe("f(x)=x; f(1)", "Ok(1)")
+})
--- a/packages/squiggle-lang/tests/Reducer/Reducer_functionTricks_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_functionTricks_test.res
@ -0,0 +1,77 @@
+open Jest
+open Reducer_TestHelpers
+
+describe("Arity check", () => {
+  testEvalToBe("f(x,y) = x + y; f(1,2)", "Ok(3)")
+  testEvalToBe(
+    "f(x,y) = x + y; f(1)",
+    "Error(2 arguments expected. Instead 1 argument(s) were passed.)",
+  )
+  testEvalToBe(
+    "f(x,y) = x + y; f(1,2,3)",
+    "Error(2 arguments expected. Instead 3 argument(s) were passed.)",
+  )
+  testEvalToBe(
+    "f(x,y)=x+y; f(1,2,3,4)",
+    "Error(2 arguments expected. Instead 4 argument(s) were passed.)",
+  )
+  testEvalToBe(
+    "f(x,y)=x+y; f(1)",
+    "Error(2 arguments expected. Instead 1 argument(s) were passed.)",
+  )
+  testEvalToBe(
+    "f(x,y)=x(y); f(f)",
+    "Error(2 arguments expected. Instead 1 argument(s) were passed.)",
+  )
+  testEvalToBe("f(x)=x; f(f)", "Ok(lambda(x=>internal code))")
+  testEvalToBe(
+    "f(x,y)=x(y); f(z)",
+    "Error(2 arguments expected. Instead 1 argument(s) were passed.)",
+  )
+})
+
+describe("symbol not defined", () => {
+  testEvalToBe("f(x)=x(y); f(f)", "Error(y is not defined)")
+  testEvalToBe("f(x)=x; f(f)", "Ok(lambda(x=>internal code))")
+  testEvalToBe("f(x)=x(y); f(z)", "Error(z is not defined)")
+  testEvalToBe("f(x)=x(y); f(2)", "Error(2 is not a function)")
+  testEvalToBe("f(x)=x(1); f(2)", "Error(2 is not a function)")
+})
+
+describe("call and bindings", () => {
+  testEvalToBe("f(x)=x+1", "Ok({f: lambda(x=>internal code)})")
+  testEvalToBe("f(x)=x+1; f(1)", "Ok(2)")
+  testEvalToBe("f=1;y=2", "Ok({f: 1,y: 2})")
+  testEvalToBe("f(x)=x+1; y=f(1)", "Ok({f: lambda(x=>internal code),y: 2})")
+  testEvalToBe("f(x)=x+1; y=f(1); f(1)", "Ok(2)")
+  testEvalToBe("f(x)=x+1; y=f(1); z=f(1)", "Ok({f: lambda(x=>internal code),y: 2,z: 2})")
+  testEvalToBe(
+    "f(x)=x+1; g(x)=f(x)+1",
+    "Ok({f: lambda(x=>internal code),g: lambda(x=>internal code)})",
+  )
+  testParseToBe(
+    "f=99; g(x)=f; g(2)",
+    "Ok((:$$block (:$$block (:$let :f 99) (:$let :g (:$$lambda [x] (:$$block :f))) (:g 2))))",
+  )
+  testEvalToBe("f=99; g(x)=f; g(2)", "Ok(99)")
+  testEvalToBe("f(x)=x; g(x)=f(x); g(2)", "Ok(2)")
+  testEvalToBe(
+    "f(x)=x+1; g(x)=f(x)+1; y=g(2)",
+    "Ok({f: lambda(x=>internal code),g: lambda(x=>internal code),y: 4})",
+  )
+  testEvalToBe("f(x)=x+1; g(x)=f(x)+1; g(2)", "Ok(4)")
+})
+
+describe("function trics", () => {
+  testParseToBe(
+    "f(x)=f(y)=2; f(2)",
+    "Ok((:$$block (:$$block (:$let :f (:$$lambda [x] (:$$block (:$let :f (:$$lambda [y] (:$$block 2)))))) (:f 2))))",
+  )
+  testEvalToBe("f(x)=f(y)=2; f(2)", "Ok({f: lambda(y=>internal code),x: 2})")
+  testEvalToBe("y=2;g(x)=y+1;g(2)", "Ok(3)")
+  testEvalToBe("y=2;g(x)=inspect(y)+1", "Ok({g: lambda(x=>internal code),y: 2})")
+  MySkip.testEvalToBe("f(x) = x(x); f(f)", "????") // TODO: Infinite loop. Any solution? Catching proper exception or timeout?
+  MySkip.testEvalToBe("f(x, x)=x+x; f(1,2)", "????") // TODO: Duplicate parameters
+  MySkip.testEvalToBe("myadd(x,y)=x+y; z=[add]; z[0](3,2)", "????") //TODO: to fix with new parser
+  MySkip.testEvalToBe("myaddd(x,y)=x+y; z={x: add}; z.x(3,2)", "????") //TODO: to fix with new parser
+})
--- a/packages/squiggle-lang/tests/Reducer/Reducer_test.res
+++ b/packages/squiggle-lang/tests/Reducer/Reducer_test.res
@ -10,46 +10,39 @@ describe("reducer using mathjs parse", () => {
  // Those tests toString that we are converting mathjs parse tree to what we need

  describe("expressions", () => {
-    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)))")
+    testParseToBe("1", "Ok((:$$block 1))")
+    testParseToBe("(1)", "Ok((:$$block 1))")
+    testParseToBe("1+2", "Ok((:$$block (:add 1 2)))")
+    testParseToBe("1+2*3", "Ok((:$$block (: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)
-    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)))")
+    testDescriptionParseToBe("empty", "[]", "Ok((:$$block ()))")
+    testParseToBe("[1, 2, 3]", "Ok((:$$block (1 2 3)))")
+    testParseToBe("['hello', 'world']", "Ok((:$$block ('hello' 'world')))")
+    testDescriptionParseToBe("index", "([0,1,2])[1]", "Ok((:$$block (:$atIndex (0 1 2) (1))))")
  })
  describe("records", () => {
-    testDescriptionParseToBe("define", "{a: 1, b: 2}", "Ok((:$constructRecord (('a' 1) ('b' 2))))")
+    testDescriptionParseToBe(
+      "define",
+      "{a: 1, b: 2}",
+      "Ok((:$$block (:$constructRecord (('a' 1) ('b' 2)))))",
+    )
    testDescriptionParseToBe(
      "use",
      "{a: 1, b: 2}.a",
-      "Ok((:$atIndex (:$constructRecord (('a' 1) ('b' 2))) ('a')))",
+      "Ok((:$$block (:$atIndex (:$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)))",
-    )
+    testParseToBe("1; 2", "Ok((:$$block (:$$block 1 2)))")
+    testParseToBe("1+1; 2+1", "Ok((:$$block (:$$block (: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)))",
-    )
+    testParseToBe("x=1; x", "Ok((:$$block (:$$block (:$let :x 1) :x)))")
+    testParseToBe("x=1+1; x+1", "Ok((:$$block (:$$block (:$let :x (:add 1 1)) (:add :x 1))))")
  })
 })

@ -70,13 +63,13 @@ describe("eval", () => {
  })
  describe("arrays", () => {
    test("empty array", () => expectEvalToBe("[]", "Ok([])"))
-    testEvalToBe("[1, 2, 3]", "Ok([1, 2, 3])")
-    testEvalToBe("['hello', 'world']", "Ok(['hello', 'world'])")
+    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("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)"))
  })
@ -91,7 +84,7 @@ describe("eval", () => {
    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)")
+    testEvalToBe("x=1; x=1", "Ok({x: 1})")
  })
 })

--- a/packages/squiggle-lang/tests/ReducerInterface/ReducerInterface_Distribution_test.res
+++ b/packages/squiggle-lang/tests/ReducerInterface/ReducerInterface_Distribution_test.res
@ -119,27 +119,34 @@ describe("eval on distribution functions", () => {

 describe("parse on distribution functions", () => {
  describe("power", () => {
-    testParse("normal(5,2) ^ normal(5,1)", "Ok((:pow (:normal 5 2) (:normal 5 1)))")
-    testParse("3 ^ normal(5,1)", "Ok((:pow 3 (:normal 5 1)))")
-    testParse("normal(5,2) ^ 3", "Ok((:pow (:normal 5 2) 3))")
+    testParse("normal(5,2) ^ normal(5,1)", "Ok((:$$block (:pow (:normal 5 2) (:normal 5 1))))")
+    testParse("3 ^ normal(5,1)", "Ok((:$$block (:pow 3 (:normal 5 1))))")
+    testParse("normal(5,2) ^ 3", "Ok((:$$block (:pow (:normal 5 2) 3)))")
  })
  describe("subtraction", () => {
-    testParse("10 - normal(5,1)", "Ok((:subtract 10 (:normal 5 1)))")
-    testParse("normal(5,1) - 10", "Ok((:subtract (:normal 5 1) 10))")
+    testParse("10 - normal(5,1)", "Ok((:$$block (:subtract 10 (:normal 5 1))))")
+    testParse("normal(5,1) - 10", "Ok((:$$block (:subtract (:normal 5 1) 10)))")
  })
  describe("pointwise arithmetic expressions", () => {
    testParse(~skip=true, "normal(5,2) .+ normal(5,1)", "Ok((:dotAdd (:normal 5 2) (:normal 5 1)))")
    testParse(
      ~skip=true,
      "normal(5,2) .- normal(5,1)",
-      "Ok((:dotSubtract (:normal 5 2) (:normal 5 1)))",
+      "Ok((:$$block (:dotSubtract (:normal 5 2) (:normal 5 1))))",
+      // TODO: !!! returns "Ok((:$$block (:dotPow (:normal 5 2) (:normal 5 1))))"
    )
-    testParse("normal(5,2) .* normal(5,1)", "Ok((:dotMultiply (:normal 5 2) (:normal 5 1)))")
-    testParse("normal(5,2) ./ normal(5,1)", "Ok((:dotDivide (:normal 5 2) (:normal 5 1)))")
-    testParse("normal(5,2) .^ normal(5,1)", "Ok((:dotPow (:normal 5 2) (:normal 5 1)))")
+    testParse(
+      "normal(5,2) .* normal(5,1)",
+      "Ok((:$$block (:dotMultiply (:normal 5 2) (:normal 5 1))))",
+    )
+    testParse(
+      "normal(5,2) ./ normal(5,1)",
+      "Ok((:$$block (:dotDivide (:normal 5 2) (:normal 5 1))))",
+    )
+    testParse("normal(5,2) .^ normal(5,1)", "Ok((:$$block (:dotPow (:normal 5 2) (:normal 5 1))))")
  })
  describe("equality", () => {
-    testParse("5 == normal(5,2)", "Ok((:equal 5 (:normal 5 2)))")
+    testParse("5 == normal(5,2)", "Ok((:$$block (:equal 5 (:normal 5 2))))")
  })
  describe("pointwise adding two normals", () => {
    testParse(~skip=true, "normal(5,2) .+ normal(5,1)", "Ok((:dotAdd (:normal 5 2) (:normal 5 1)))")
--- a/packages/squiggle-lang/tests/ReducerInterface/ReducerInterface_ExpressionValue_test.res
+++ b/packages/squiggle-lang/tests/ReducerInterface/ReducerInterface_ExpressionValue_test.res
@ -3,9 +3,9 @@ open Jest
 open Expect

 describe("ExpressionValue", () => {
-  test("argsToString", () => expect([EvNumber(1.), EvString("a")]->argsToString)->toBe("1, 'a'"))
+  test("argsToString", () => expect([EvNumber(1.), EvString("a")]->argsToString)->toBe("1,'a'"))

  test("toStringFunctionCall", () =>
-    expect(("fn", [EvNumber(1.), EvString("a")])->toStringFunctionCall)->toBe("fn(1, 'a')")
+    expect(("fn", [EvNumber(1.), EvString("a")])->toStringFunctionCall)->toBe("fn(1,'a')")
  )
 })
--- a/packages/squiggle-lang/package.json
+++ b/packages/squiggle-lang/package.json
@ -4,7 +4,9 @@
  "homepage": "https://squiggle-language.com",
  "license": "MIT",
  "scripts": {
-    "build": "rescript build -with-deps && tsc",
+    "build": "yarn build:rescript && yarn build:typescript",
+    "build:rescript": "rescript build -with-deps",
+    "build:typescript": "tsc",
    "bundle": "webpack",
    "start": "rescript build -w -with-deps",
    "clean": "rescript clean && rm -r dist",
--- a/packages/squiggle-lang/src/js/distribution.ts
+++ b/packages/squiggle-lang/src/js/distribution.ts
@ -3,7 +3,7 @@ import {
  genericDist,
  continuousShape,
  discreteShape,
-  samplingParams,
+  environment,
  distributionError,
  toPointSet,
  distributionErrorToString,
@ -51,9 +51,9 @@ export type shape = {

 export class Distribution {
  t: genericDist;
-  env: samplingParams;
+  env: environment;

-  constructor(t: genericDist, env: samplingParams) {
+  constructor(t: genericDist, env: environment) {
    this.t = t;
    this.env = env;
    return this;
--- a/packages/squiggle-lang/src/js/index.ts
+++ b/packages/squiggle-lang/src/js/index.ts
@ -1,8 +1,10 @@
 import * as _ from "lodash";
 import {
  samplingParams,
-  evaluateUsingExternalBindings,
+  environment,
+  defaultEnvironment,
  evaluatePartialUsingExternalBindings,
+  evaluateUsingOptions,
  externalBindings,
  expressionValue,
  errorValue,
@ -39,33 +41,34 @@ export let defaultSamplingInputs: samplingParams = {
 export function run(
  squiggleString: string,
  bindings?: externalBindings,
-  samplingInputs?: samplingParams,
+  environment?: environment,
  imports?: jsImports
 ): result<squiggleExpression, errorValue> {
  let b = bindings ? bindings : defaultBindings;
  let i = imports ? imports : defaultImports;
-  let si: samplingParams = samplingInputs
-    ? samplingInputs
-    : defaultSamplingInputs;
-
-  let result: result<expressionValue, errorValue> =
-    evaluateUsingExternalBindings(squiggleString, mergeImports(b, i));
-  return resultMap(result, (x) => createTsExport(x, si));
+  let e = environment ? environment : defaultEnvironment;
+  let res: result<expressionValue, errorValue> = evaluateUsingOptions(
+    { externalBindings: mergeImports(b, i), environment: e },
+    squiggleString
+  );
+  return resultMap(res, (x) => createTsExport(x, e));
 }

 // Run Partial. A partial is a block of code that doesn't return a value
 export function runPartial(
  squiggleString: string,
  bindings?: externalBindings,
-  _samplingInputs?: samplingParams,
+  environment?: environment,
  imports?: jsImports
 ): result<externalBindings, errorValue> {
  let b = bindings ? bindings : defaultBindings;
  let i = imports ? imports : defaultImports;
+  let e = environment ? environment : defaultEnvironment;

  return evaluatePartialUsingExternalBindings(
    squiggleString,
-    mergeImports(b, i)
+    mergeImports(b, i),
+    e
  );
 }

@ -89,7 +92,7 @@ export let defaultBindings: externalBindings = {};

 function createTsExport(
  x: expressionValue,
-  sampEnv: samplingParams
+  environment: environment
 ): squiggleExpression {
  switch (x.tag) {
    case "EvArray":
@ -108,7 +111,10 @@ function createTsExport(
              return tag(
                "record",
                _.mapValues(arrayItem.value, (recordValue: unknown) =>
-                  convertRawToTypescript(recordValue as rescriptExport, sampEnv)
+                  convertRawToTypescript(
+                    recordValue as rescriptExport,
+                    environment
+                  )
                )
              );
            case "EvArray":
@ -116,20 +122,24 @@ function createTsExport(
              return tag(
                "array",
                y.map((childArrayItem) =>
-                  convertRawToTypescript(childArrayItem, sampEnv)
+                  convertRawToTypescript(childArrayItem, environment)
                )
              );
            default:
-              return createTsExport(arrayItem, sampEnv);
+              return createTsExport(arrayItem, environment);
          }
        })
      );
+    case "EvArrayString":
+      return tag("arraystring", x.value);
    case "EvBool":
      return tag("boolean", x.value);
    case "EvCall":
      return tag("call", x.value);
+    case "EvLambda":
+      return tag("lambda", x.value);
    case "EvDistribution":
-      return tag("distribution", new Distribution(x.value, sampEnv));
+      return tag("distribution", new Distribution(x.value, environment));
    case "EvNumber":
      return tag("number", x.value);
    case "EvRecord":
@ -137,7 +147,7 @@ function createTsExport(
      let result: tagged<"record", { [key: string]: squiggleExpression }> = tag(
        "record",
        _.mapValues(x.value, (x: unknown) =>
-          convertRawToTypescript(x as rescriptExport, sampEnv)
+          convertRawToTypescript(x as rescriptExport, environment)
        )
      );
      return result;
--- a/packages/squiggle-lang/src/js/rescript_interop.ts
+++ b/packages/squiggle-lang/src/js/rescript_interop.ts
@ -3,10 +3,11 @@ import {
  mixedShape,
  sampleSetDist,
  genericDist,
-  samplingParams,
+  environment,
  symbolicDist,
  discreteShape,
  continuousShape,
+  lambdaValue,
 } from "../rescript/TypescriptInterface.gen";
 import { Distribution } from "./distribution";
 import { tagged, tag } from "./types";
@ -19,31 +20,39 @@ export type rescriptExport =
      _0: rescriptExport[];
    }
  | {
-      TAG: 1; // EvBool
+      TAG: 1; // EvString
+      _0: string[];
+    }
+  | {
+      TAG: 2; // EvBool
      _0: boolean;
    }
  | {
-      TAG: 2; // EvCall
+      TAG: 3; // EvCall
      _0: string;
    }
  | {
-      TAG: 3; // EvDistribution
+      TAG: 4; // EvDistribution
      _0: rescriptDist;
    }
  | {
-      TAG: 4; // EvNumber
+      TAG: 5; // EvLambda
+      _0: lambdaValue;
+    }
+  | {
+      TAG: 6; // EvNumber
      _0: number;
    }
  | {
-      TAG: 5; // EvRecord
+      TAG: 7; // EvRecord
      _0: { [key: string]: rescriptExport };
    }
  | {
-      TAG: 6; // EvString
+      TAG: 8; // EvString
      _0: string;
    }
  | {
-      TAG: 7; // EvSymbol
+      TAG: 9; // EvSymbol
      _0: string;
    };

@ -70,7 +79,9 @@ export type squiggleExpression =
  | tagged<"symbol", string>
  | tagged<"string", string>
  | tagged<"call", string>
+  | tagged<"lambda", lambdaValue>
  | tagged<"array", squiggleExpression[]>
+  | tagged<"arraystring", string[]>
  | tagged<"boolean", boolean>
  | tagged<"distribution", Distribution>
  | tagged<"number", number>
@ -78,36 +89,40 @@ export type squiggleExpression =

 export function convertRawToTypescript(
  result: rescriptExport,
-  sampEnv: samplingParams
+  environment: environment
 ): squiggleExpression {
  switch (result.TAG) {
    case 0: // EvArray
      return tag(
        "array",
-        result._0.map((x) => convertRawToTypescript(x, sampEnv))
+        result._0.map((x) => convertRawToTypescript(x, environment))
      );
-    case 1: // EvBool
+    case 1: // EvArrayString
+      return tag("arraystring", result._0);
+    case 2: // EvBool
      return tag("boolean", result._0);
-    case 2: // EvCall
+    case 3: // EvCall
      return tag("call", result._0);
-    case 3: // EvDistribution
+    case 4: // EvDistribution
      return tag(
        "distribution",
        new Distribution(
          convertRawDistributionToGenericDist(result._0),
-          sampEnv
+          environment
        )
      );
-    case 4: // EvNumber
+    case 5: // EvDistribution
+      return tag("lambda", result._0);
+    case 6: // EvNumber
      return tag("number", result._0);
-    case 5: // EvRecord
+    case 7: // EvRecord
      return tag(
        "record",
-        _.mapValues(result._0, (x) => convertRawToTypescript(x, sampEnv))
+        _.mapValues(result._0, (x) => convertRawToTypescript(x, environment))
      );
-    case 6: // EvString
+    case 8: // EvString
      return tag("string", result._0);
-    case 7: // EvSymbol
+    case 9: // EvSymbol
      return tag("symbol", result._0);
  }
 }
@ -141,15 +156,15 @@ export type jsValue =

 export function jsValueToBinding(value: jsValue): rescriptExport {
  if (typeof value === "boolean") {
-    return { TAG: 1, _0: value as boolean };
+    return { TAG: 2, _0: value as boolean };
  } else if (typeof value === "string") {
-    return { TAG: 6, _0: value as string };
+    return { TAG: 8, _0: value as string };
  } else if (typeof value === "number") {
-    return { TAG: 4, _0: value as number };
+    return { TAG: 6, _0: value as number };
  } else if (Array.isArray(value)) {
    return { TAG: 0, _0: value.map(jsValueToBinding) };
  } else {
    // Record
-    return { TAG: 5, _0: _.mapValues(value, jsValueToBinding) };
+    return { TAG: 7, _0: _.mapValues(value, jsValueToBinding) };
  }
 }
--- a/packages/squiggle-lang/src/rescript/Distributions/DistributionOperation/DistributionOperation.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/DistributionOperation/DistributionOperation.res
@ -9,6 +9,11 @@ type env = {
  xyPointLength: int,
 }

+let defaultEnv = {
+  sampleCount: 10000,
+  xyPointLength: 10000,
+}
+
 type outputType =
  | Dist(genericDist)
  | Float(float)
--- a/packages/squiggle-lang/src/rescript/Distributions/DistributionOperation/DistributionOperation.resi
+++ b/packages/squiggle-lang/src/rescript/Distributions/DistributionOperation/DistributionOperation.resi
@ -4,6 +4,9 @@ type env = {
  xyPointLength: int,
 }

+@genType
+let defaultEnv: env
+
 open DistributionTypes

@genType
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
@ -1,15 +1,11 @@
-module Dispatch = Reducer_Dispatch
 module ErrorValue = Reducer_ErrorValue
 module Expression = Reducer_Expression
-module Extra = Reducer_Extra
-module Js = Reducer_Js
-module MathJs = Reducer_MathJs

-type expressionValue = Reducer_Expression.expressionValue
-type externalBindings = Expression.externalBindings
-let evaluate = Expression.eval
-let evaluateUsingExternalBindings = Expression.evalUsingExternalBindings
-let evaluatePartialUsingExternalBindings = Expression.evalPartialUsingExternalBindings
+type environment = ReducerInterface_ExpressionValue.environment
+type errorValue = Reducer_ErrorValue.errorValue
+type expressionValue = ReducerInterface_ExpressionValue.expressionValue
+type externalBindings = ReducerInterface_ExpressionValue.externalBindings
+let evaluate = Expression.evaluate
+let evaluateUsingOptions = Expression.evaluateUsingOptions
+let evaluatePartialUsingExternalBindings = Expression.evaluatePartialUsingExternalBindings
 let parse = Expression.parse
-let parseOuter = Expression.parseOuter
-let parsePartial = Expression.parsePartial
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
@ -1,26 +1,28 @@
-module Dispatch = Reducer_Dispatch
 module ErrorValue = Reducer_ErrorValue
 module Expression = Reducer_Expression
-module Extra = Reducer_Extra
-module Js = Reducer_Js
-module MathJs = Reducer_MathJs

+@genType
+type environment = ReducerInterface_ExpressionValue.environment
+@genType
+type errorValue = Reducer_ErrorValue.errorValue
@genType
 type expressionValue = ReducerInterface_ExpressionValue.expressionValue
@genType
 type externalBindings = ReducerInterface_ExpressionValue.externalBindings
+
@genType
-let evaluate: string => result<expressionValue, Reducer_ErrorValue.errorValue>
-@genType
-let evaluateUsingExternalBindings: (
+let evaluateUsingOptions: (
+  ~environment: option<QuriSquiggleLang.ReducerInterface_ExpressionValue.environment>,
+  ~externalBindings: option<QuriSquiggleLang.ReducerInterface_ExpressionValue.externalBindings>,
  string,
-  externalBindings,
-) => result<expressionValue, Reducer_ErrorValue.errorValue>
+) => result<expressionValue, errorValue>
@genType
 let evaluatePartialUsingExternalBindings: (
  string,
-  externalBindings,
-) => result<externalBindings, Reducer_ErrorValue.errorValue>
-let parse: string => result<Expression.expression, ErrorValue.errorValue>
-let parseOuter: string => result<Expression.expression, ErrorValue.errorValue>
-let parsePartial: string => result<Expression.expression, ErrorValue.errorValue>
+  QuriSquiggleLang.ReducerInterface_ExpressionValue.externalBindings,
+  QuriSquiggleLang.ReducerInterface_ExpressionValue.environment,
+) => result<externalBindings, errorValue>
+@genType
+let evaluate: string => result<expressionValue, errorValue>
+
+let parse: string => result<Expression.expression, 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
@ -1,5 +1,6 @@
 module ExternalLibrary = ReducerInterface.ExternalLibrary
 module MathJs = Reducer_MathJs
+module Bindings = Reducer_Expression_Bindings
 open ReducerInterface.ExpressionValue
 open Reducer_ErrorValue

@ -11,7 +12,7 @@ open Reducer_ErrorValue

 exception TestRescriptException

-let callInternal = (call: functionCall): result<'b, errorValue> => {
+let callInternal = (call: functionCall, _environment): result<'b, errorValue> => {
  let callMathJs = (call: functionCall): result<'b, errorValue> =>
    switch call {
    | ("javascriptraise", [msg]) => Js.Exn.raiseError(toString(msg)) // For Tests
@ -20,12 +21,12 @@ let callInternal = (call: functionCall): result<'b, errorValue> => {
    }

  let constructRecord = arrayOfPairs => {
-    Belt.Array.map(arrayOfPairs, pairValue => {
+    Belt.Array.map(arrayOfPairs, pairValue =>
      switch pairValue {
      | EvArray([EvString(key), valueValue]) => (key, valueValue)
      | _ => ("wrong key type", pairValue->toStringWithType->EvString)
      }
-    })
+    )
    ->Js.Dict.fromArray
    ->EvRecord
    ->Ok
@ -43,16 +44,58 @@ let callInternal = (call: functionCall): result<'b, errorValue> => {
    | None => RERecordPropertyNotFound("Record property not found", sIndex)->Error
    }

+  let inspect = (value: expressionValue) => {
+    Js.log(value->toString)
+    value->Ok
+  }
+
+  let inspectLabel = (value: expressionValue, label: string) => {
+    Js.log(`${label}: ${value->toString}`)
+    value->Ok
+  }
+
+  /*
+    NOTE: This function is cancelled. The related issue is
+    https://github.com/webpack/webpack/issues/13435
+ */
+  let inspectPerformance = (value: expressionValue, label: string) => {
+    // let _ = %raw("{performance} = require('perf_hooks')")
+    // let start = %raw(`performance.now()`)
+    // let finish = %raw(`performance.now()`)
+    // let performance = finish - start
+    // Js.log(`${label}: ${value->toString} performance: ${Js.String.make(performance)}ms`)
+    // TODO find a way of failing the hook gracefully, also needs a block parameter
+    Js.log(`${label}: ${value->toString}`)
+    value->Ok
+  }
+
+  let doSetBindings = (
+    externalBindings: externalBindings,
+    symbol: string,
+    value: expressionValue,
+  ) => {
+    Bindings.fromExternalBindings(externalBindings)
+    ->Belt.Map.String.set(symbol, value)
+    ->Bindings.toExternalBindings
+    ->EvRecord
+    ->Ok
+  }
+
+  let doExportBindings = (externalBindings: externalBindings) => EvRecord(externalBindings)->Ok
+
  switch call {
-  // | ("$constructRecord", pairArray)
-  // | ("$atIndex", [EvArray(anArray), EvNumber(fIndex)]) => arrayAtIndex(anArray, fIndex)
-  // | ("$atIndex", [EvRecord(aRecord), EvString(sIndex)]) => recordAtIndex(aRecord, sIndex)
-  | ("$constructRecord", [EvArray(arrayOfPairs)]) => constructRecord(arrayOfPairs)
  | ("$atIndex", [EvArray(aValueArray), EvArray([EvNumber(fIndex)])]) =>
    arrayAtIndex(aValueArray, fIndex)
  | ("$atIndex", [EvRecord(dict), EvArray([EvString(sIndex)])]) => recordAtIndex(dict, sIndex)
  | ("$atIndex", [obj, index]) =>
    (toStringWithType(obj) ++ "??~~~~" ++ toStringWithType(index))->EvString->Ok
+  | ("$constructRecord", [EvArray(arrayOfPairs)]) => constructRecord(arrayOfPairs)
+  | ("inspect", [value, EvString(label)]) => inspectLabel(value, label)
+  | ("inspect", [value]) => inspect(value)
+  | ("inspectPerformance", [value, EvString(label)]) => inspectPerformance(value, label)
+  | ("$setBindings", [EvRecord(externalBindings), EvSymbol(symbol), value]) =>
+    doSetBindings(externalBindings, symbol, value)
+  | ("$exportBindings", [EvRecord(externalBindings)]) => doExportBindings(externalBindings)
  | call => callMathJs(call)
  }
 }
@ -60,12 +103,12 @@ let callInternal = (call: functionCall): result<'b, errorValue> => {
 /*
  Reducer uses Result monad while reducing expressions
 */
-let dispatch = (call: functionCall): result<expressionValue, errorValue> =>
+let dispatch = (call: functionCall, environment): result<expressionValue, errorValue> =>
  try {
    let (fn, args) = call
    // There is a bug that prevents string match in patterns
    // So we have to recreate a copy of the string
-    ExternalLibrary.dispatch((Js.String.make(fn), args), callInternal)
+    ExternalLibrary.dispatch((Js.String.make(fn), args), environment, callInternal)
  } catch {
  | Js.Exn.Error(obj) => REJavaScriptExn(Js.Exn.message(obj), Js.Exn.name(obj))->Error
  | _ => RETodo("unhandled rescript exception")->Error
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
@ -3,120 +3,170 @@
  they take expressions as parameters and return a new expression.
  Macros are used to define language building blocks. They are like Lisp macros.
 */
+module Bindings = Reducer_Expression_Bindings
 module ExpressionT = Reducer_Expression_T
 module ExpressionValue = ReducerInterface.ExpressionValue
+module ExpressionWithContext = Reducer_ExpressionWithContext
 module Result = Belt.Result
+open Reducer_Expression_ExpressionBuilder

-open Reducer_ErrorValue
-
+type environment = ExpressionValue.environment
+type errorValue = Reducer_ErrorValue.errorValue
 type expression = ExpressionT.expression
-
-type reducerFn = (
-  expression,
-  ExpressionT.bindings,
-) => result<ExpressionValue.expressionValue, errorValue>
+type expressionValue = ExpressionValue.expressionValue
+type expressionWithContext = ExpressionWithContext.expressionWithContext

 let dispatchMacroCall = (
-  list: list<expression>,
+  macroExpression: expression,
  bindings: ExpressionT.bindings,
-  reduceExpression: reducerFn,
-): result<expression, 'e> => {
-  let rec replaceSymbols = (expression: expression, bindings: ExpressionT.bindings): result<
-    expression,
-    errorValue,
-  > =>
-    switch expression {
-    | ExpressionT.EValue(EvSymbol(aSymbol)) =>
-      switch bindings->Belt.Map.String.get(aSymbol) {
-      | Some(boundExpression) => boundExpression->Ok
-      | None => RESymbolNotFound(aSymbol)->Error
-      }
-    | ExpressionT.EValue(_) => expression->Ok
-    | ExpressionT.EBindings(_) => expression->Ok
-    | ExpressionT.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->ExpressionT.EList)
-      }
-    }
-
-  let doBindStatement = (statement: expression, bindings: ExpressionT.bindings) => {
+  environment,
+  reduceExpression: ExpressionT.reducerFn,
+): result<expressionWithContext, errorValue> => {
+  let doBindStatement = (bindingExpr: expression, statement: expression, environment) =>
    switch statement {
-    | ExpressionT.EList(list{
-        ExpressionT.EValue(EvCall("$let")),
-        ExpressionT.EValue(EvSymbol(aSymbol)),
-        expressionToReduce,
-      }) => {
-        let rNewExpressionToReduce = replaceSymbols(expressionToReduce, bindings)
+    | ExpressionT.EList(list{ExpressionT.EValue(EvCall("$let")), symbolExpr, statement}) => {
+        let rExternalBindingsValue = reduceExpression(bindingExpr, bindings, environment)

-        let rNewValue =
-          rNewExpressionToReduce->Result.flatMap(newExpressionToReduce =>
-            reduceExpression(newExpressionToReduce, bindings)
+        rExternalBindingsValue->Result.flatMap(externalBindingsValue => {
+          let newBindings = Bindings.fromValue(externalBindingsValue)
+
+          // Js.log(
+          //   `bindStatement ${Bindings.toString(newBindings)}<==${ExpressionT.toString(
+          //       bindingExpr,
+          //     )} statement: $let ${ExpressionT.toString(symbolExpr)}=${ExpressionT.toString(
+          //       statement,
+          //     )}`,
+          // )
+
+          let rNewStatement = Bindings.replaceSymbols(newBindings, statement)
+          rNewStatement->Result.map(newStatement =>
+            ExpressionWithContext.withContext(
+              eFunction(
+                "$setBindings",
+                list{newBindings->Bindings.toExternalBindings->eRecord, symbolExpr, newStatement},
+              ),
+              newBindings,
+            )
          )
-
-        let rNewExpression = rNewValue->Result.map(newValue => ExpressionT.EValue(newValue))
-        rNewExpression->Result.map(newExpression =>
-          Belt.Map.String.set(bindings, aSymbol, newExpression)->ExpressionT.EBindings
-        )
+        })
      }
    | _ => REAssignmentExpected->Error
    }
-  }

-  let doExportVariableExpression = (bindings: ExpressionT.bindings) => {
-    let emptyDictionary: Js.Dict.t<ExpressionValue.expressionValue> = Js.Dict.empty()
-    let reducedBindings = bindings->Belt.Map.String.keep((_key, value) =>
-      switch value {
-      | ExpressionT.EValue(_) => true
-      | _ => false
-      }
-    )
-    let externalBindings = reducedBindings->Belt.Map.String.reduce(emptyDictionary, (
-      acc,
-      key,
-      expressionValue,
-    ) => {
-      let value = switch expressionValue {
-      | EValue(aValue) => aValue
-      | _ => EvSymbol("internal")
-      }
-      Js.Dict.set(acc, key, value)
-      acc
-    })
-    externalBindings->ExpressionValue.EvRecord->ExpressionT.EValue->Ok
-  }
+  let doBindExpression = (bindingExpr: expression, statement: expression, environment): result<
+    expressionWithContext,
+    errorValue,
+  > =>
+    switch statement {
+    | ExpressionT.EList(list{ExpressionT.EValue(EvCall("$let")), symbolExpr, statement}) => {
+        let rExternalBindingsValue = reduceExpression(bindingExpr, bindings, environment)

-  let doBindExpression = (expression: expression, bindings: ExpressionT.bindings) =>
-    switch expression {
-    | ExpressionT.EList(list{ExpressionT.EValue(EvCall("$let")), ..._}) =>
-      REExpressionExpected->Error
-    | ExpressionT.EList(list{ExpressionT.EValue(EvCall("$exportVariablesExpression"))}) =>
-      doExportVariableExpression(bindings)
-    | _ => replaceSymbols(expression, bindings)
+        rExternalBindingsValue->Result.flatMap(externalBindingsValue => {
+          let newBindings = Bindings.fromValue(externalBindingsValue)
+          let rNewStatement = Bindings.replaceSymbols(newBindings, statement)
+          rNewStatement->Result.map(newStatement =>
+            ExpressionWithContext.withContext(
+              eFunction(
+                "$exportBindings",
+                list{
+                  eFunction(
+                    "$setBindings",
+                    list{
+                      newBindings->Bindings.toExternalBindings->eRecord,
+                      symbolExpr,
+                      newStatement,
+                    },
+                  ),
+                },
+              ),
+              newBindings,
+            )
+          )
+        })
+      }
+    | _ => {
+        let rExternalBindingsValue: result<expressionValue, errorValue> = reduceExpression(
+          bindingExpr,
+          bindings,
+          environment,
+        )
+
+        rExternalBindingsValue->Result.flatMap(externalBindingsValue => {
+          let newBindings = Bindings.fromValue(externalBindingsValue)
+          let rNewStatement = Bindings.replaceSymbols(newBindings, statement)
+          rNewStatement->Result.map(newStatement =>
+            ExpressionWithContext.withContext(newStatement, newBindings)
+          )
+        })
+      }
    }

-  switch list {
-  | list{ExpressionT.EValue(EvCall("$$bindings"))} => bindings->ExpressionT.EBindings->Ok
+  let doBlock = (exprs: list<expression>, _bindings: ExpressionT.bindings, _environment): result<
+    expressionWithContext,
+    errorValue,
+  > => {
+    let exprsArray = Belt.List.toArray(exprs)
+    let maxIndex = Js.Array2.length(exprsArray) - 1
+    let newStatement = exprsArray->Js.Array2.reducei((acc, statement, index) =>
+      if index == 0 {
+        if index == maxIndex {
+          eBindExpressionDefault(statement)
+        } else {
+          eBindStatementDefault(statement)
+        }
+      } else if index == maxIndex {
+        eBindExpression(acc, statement)
+      } else {
+        eBindStatement(acc, statement)
+      }
+    , eSymbol("undefined block"))
+    ExpressionWithContext.noContext(newStatement)->Ok
+  }

-  | list{
-      ExpressionT.EValue(EvCall("$$bindStatement")),
-      ExpressionT.EBindings(bindings),
-      statement,
-    } =>
-    doBindStatement(statement, bindings)
-  | list{
-      ExpressionT.EValue(EvCall("$$bindExpression")),
-      ExpressionT.EBindings(bindings),
-      expression,
-    } =>
-    doBindExpression(expression, bindings)
-  | _ => list->ExpressionT.EList->Ok
+  let doLambdaDefinition = (
+    bindings: ExpressionT.bindings,
+    parameters: array<string>,
+    lambdaDefinition: ExpressionT.expression,
+  ) =>
+    ExpressionWithContext.noContext(
+      eLambda(parameters, bindings->Bindings.toExternalBindings, lambdaDefinition),
+    )->Ok
+
+  let expandExpressionList = (aList, bindings: ExpressionT.bindings, environment): result<
+    expressionWithContext,
+    errorValue,
+  > =>
+    switch aList {
+    | list{
+        ExpressionT.EValue(EvCall("$$bindStatement")),
+        bindingExpr: ExpressionT.expression,
+        statement,
+      } =>
+      doBindStatement(bindingExpr, statement, environment)
+    | list{ExpressionT.EValue(EvCall("$$bindStatement")), statement} =>
+      // bindings of the context are used when there is no binding expression
+      doBindStatement(eRecord(Bindings.toExternalBindings(bindings)), statement, environment)
+    | list{
+        ExpressionT.EValue(EvCall("$$bindExpression")),
+        bindingExpr: ExpressionT.expression,
+        expression,
+      } =>
+      doBindExpression(bindingExpr, expression, environment)
+    | list{ExpressionT.EValue(EvCall("$$bindExpression")), expression} =>
+      // bindings of the context are used when there is no binding expression
+      doBindExpression(eRecord(Bindings.toExternalBindings(bindings)), expression, environment)
+    | list{ExpressionT.EValue(EvCall("$$block")), ...exprs} => doBlock(exprs, bindings, environment)
+    | list{
+        ExpressionT.EValue(EvCall("$$lambda")),
+        ExpressionT.EValue(EvArrayString(parameters)),
+        lambdaDefinition,
+      } =>
+      doLambdaDefinition(bindings, parameters, lambdaDefinition)
+    | _ => ExpressionWithContext.noContext(ExpressionT.EList(aList))->Ok
+    }
+
+  switch macroExpression {
+  | EList(aList) => expandExpressionList(aList, bindings, environment)
+  | _ => ExpressionWithContext.noContext(macroExpression)->Ok
  }
 }
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
@ -1,15 +1,17 @@
@genType
 type errorValue =
+  | REArityError(option<string>, int, int) //TODO: Binding a lambda to a variable should record the variable name in lambda for error reporting
  | REArrayIndexNotFound(string, int)
  | REAssignmentExpected
+  | REDistributionError(DistributionTypes.error)
  | REExpressionExpected
  | REFunctionExpected(string)
  | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
  | REMacroNotFound(string)
+  | RENotAFunction(string)
  | RERecordPropertyNotFound(string, string)
  | RESymbolNotFound(string)
  | RESyntaxError(string)
-  | REDistributionError(DistributionTypes.error)
  | RETodo(string) // To do

 type t = errorValue
@ -17,6 +19,10 @@ type t = errorValue
@genType
 let errorToString = err =>
  switch err {
+  | REArityError(_oFnName, arity, usedArity) =>
+    `${Js.String.make(arity)} arguments expected. Instead ${Js.String.make(
+        usedArity,
+      )} argument(s) were passed.`
  | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
  | REAssignmentExpected => "Assignment expected"
  | REExpressionExpected => "Expression expected"
@ -35,6 +41,7 @@ let errorToString = err =>
      answer
    }
  | REMacroNotFound(macro) => `Macro not found: ${macro}`
+  | RENotAFunction(valueString) => `${valueString} is not a function`
  | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
  | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
  | RESyntaxError(desc) => `Syntax Error: ${desc}`
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
@ -1,35 +1,22 @@
+module Bindings = Reducer_Expression_Bindings
 module BuiltIn = Reducer_Dispatch_BuiltIn
+module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
 module ExpressionValue = ReducerInterface.ExpressionValue
 module Extra = Reducer_Extra
+module Lambda = Reducer_Expression_Lambda
+module Macro = Reducer_Expression_Macro
 module MathJs = Reducer_MathJs
 module Result = Belt.Result
 module T = Reducer_Expression_T
-open Reducer_ErrorValue

+type environment = ReducerInterface_ExpressionValue.environment
+type errorValue = Reducer_ErrorValue.errorValue
 type expression = T.expression
-type expressionValue = ExpressionValue.expressionValue
+type expressionValue = ReducerInterface_ExpressionValue.expressionValue
+type externalBindings = ReducerInterface_ExpressionValue.externalBindings
+type internalCode = ReducerInterface_ExpressionValue.internalCode
 type t = expression

-/*
-  Shows the expression as text of expression
-*/
-let rec toString = expression =>
-  switch expression {
-  | T.EBindings(_) => "$$bound"
-  | T.EList(aList) =>
-    `(${Belt.List.map(aList, aValue => toString(aValue))
-      ->Extra.List.interperse(" ")
-      ->Belt.List.toArray
-      ->Js.String.concatMany("")})`
-  | EValue(aValue) => ExpressionValue.toString(aValue)
-  }
-
-let toStringResult = codeResult =>
-  switch codeResult {
-  | Ok(a) => `Ok(${toString(a)})`
-  | Error(m) => `Error(${Js.String.make(m)})`
-  }
-
 /*
  Converts a MathJs code to expression
 */
@ -39,148 +26,115 @@ let parse_ = (expr: string, parser, converter): result<t, errorValue> =>
 let parse = (mathJsCode: string): result<t, errorValue> =>
  mathJsCode->parse_(MathJs.Parse.parse, MathJs.ToExpression.fromNode)

-let parsePartial = (mathJsCode: string): result<t, errorValue> =>
-  mathJsCode->parse_(MathJs.Parse.parse, MathJs.ToExpression.fromPartialNode)
-
-let parseOuter = (mathJsCode: string): result<t, errorValue> =>
-  mathJsCode->parse_(MathJs.Parse.parse, MathJs.ToExpression.fromOuterNode)
-
-let defaultBindings: T.bindings = Belt.Map.String.empty
-
 /*
  Recursively evaluate/reduce the expression (Lisp AST)
 */
-let rec reduceExpression = (expression: t, bindings: T.bindings): result<expressionValue, 'e> => {
-  /*
-    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 doMacroCall = (list: list<t>, bindings: T.bindings): result<t, 'e> =>
-    Reducer_Dispatch_BuiltInMacros.dispatchMacroCall(list, bindings, reduceExpression)
+let rec reduceExpression = (expression: t, bindings: T.bindings, environment: environment): result<
+  expressionValue,
+  'e,
+> => {
+  // Js.log(`reduce: ${T.toString(expression)} bindings: ${bindings->Bindings.toString}`)
+  switch expression {
+  | T.EValue(value) => value->Ok
+  | T.EList(list) =>
+    switch list {
+    | list{EValue(EvCall(fName)), ..._args} =>
+      switch Macro.isMacroName(fName) {
+      // A macro expands then reduces itself
+      | true => Macro.doMacroCall(expression, bindings, environment, reduceExpression)
+      | false => reduceExpressionList(list, bindings, environment)
+      }
+    | _ => reduceExpressionList(list, bindings, environment)
+    }
+  }
+}

-  /*
+and reduceExpressionList = (
+  expressions: list<t>,
+  bindings: T.bindings,
+  environment: environment,
+): result<expressionValue, 'e> => {
+  let racc: result<list<expressionValue>, 'e> = expressions->Belt.List.reduceReverse(Ok(list{}), (
+    racc,
+    each: expression,
+  ) =>
+    racc->Result.flatMap(acc => {
+      each
+      ->reduceExpression(bindings, environment)
+      ->Result.map(newNode => {
+        acc->Belt.List.add(newNode)
+      })
+    })
+  )
+  racc->Result.flatMap(acc => acc->reduceValueList(environment))
+}
+
+/*
    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{EvCall(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch
-    | _ => valueList->Belt.List.toArray->ExpressionValue.EvArray->Ok
-    }
+and reduceValueList = (valueList: list<expressionValue>, environment): result<
+  expressionValue,
+  'e,
+> =>
+  switch valueList {
+  | list{EvCall(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch(environment)

-  let rec seekMacros = (expression: t, bindings: T.bindings): result<t, 'e> =>
-    switch expression {
-    | T.EValue(_value) => expression->Ok
-    | T.EBindings(_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))
-      }
-    }
+  | list{EvLambda(lamdaCall), ...args} =>
+    Lambda.doLambdaCall(lamdaCall, args, environment, reduceExpression)
+  | _ =>
+    valueList
+    ->Lambda.checkIfReduced
+    ->Result.flatMap(reducedValueList =>
+      reducedValueList->Belt.List.toArray->ExpressionValue.EvArray->Ok
+    )
+  }

-  let rec reduceExpandedExpression = (expression: t): result<expressionValue, 'e> =>
-    switch expression {
-    | T.EValue(value) => value->Ok
-    | T.EList(list) => {
-        let racc: result<list<expressionValue>, 'e> = list->Belt.List.reduceReverse(Ok(list{}), (
-          racc,
-          each: expression,
-        ) =>
-          racc->Result.flatMap(acc => {
-            each
-            ->reduceExpandedExpression
-            ->Result.flatMap(newNode => {
-              acc->Belt.List.add(newNode)->Ok
-            })
-          })
-        )
-        racc->Result.flatMap(acc => acc->reduceValueList)
-      }
-    | EBindings(_bindings) => RETodo("Error: Bindings cannot be reduced to values")->Error
-    }
+let evalUsingBindingsExpression_ = (aExpression, bindings, environment): result<
+  expressionValue,
+  'e,
+> => reduceExpression(aExpression, bindings, environment)

-  let rExpandedExpression: result<t, 'e> = expression->seekMacros(bindings)
-  rExpandedExpression->Result.flatMap(expandedExpression =>
-    expandedExpression->reduceExpandedExpression
-  )
-}
+let evaluateUsingOptions = (
+  ~environment: option<ReducerInterface_ExpressionValue.environment>,
+  ~externalBindings: option<ReducerInterface_ExpressionValue.externalBindings>,
+  code: string,
+): result<expressionValue, errorValue> => {
+  let anEnvironment = switch environment {
+  | Some(env) => env
+  | None => ReducerInterface_ExpressionValue.defaultEnvironment
+  }

-let evalUsingExternalBindingsExpression_ = (aExpression, bindings): result<expressionValue, 'e> =>
-  reduceExpression(aExpression, bindings)
+  let anExternalBindings = switch externalBindings {
+  | Some(bindings) => bindings
+  | None => ReducerInterface_ExpressionValue.defaultExternalBindings
+  }

-/*
-  Evaluates MathJs code via Reducer using bindings and answers the result.
-  When bindings are used, the code is a partial code as if it is cut from a larger code.
-  Therefore all statements are assignments.
-*/
-let evalPartialUsingExternalBindings_ = (codeText: string, bindings: T.bindings) => {
-  parsePartial(codeText)->Result.flatMap(expression =>
-    expression->evalUsingExternalBindingsExpression_(bindings)
-  )
-}
+  let bindings = anExternalBindings->Bindings.fromExternalBindings

-/*
-  Evaluates MathJs code via Reducer using bindings and answers the result.
-  When bindings are used, the code is a partial code as if it is cut from a larger code.
-  Therefore all statments are assignments.
-*/
-let evalOuterWBindings_ = (codeText: string, bindings: T.bindings) => {
-  parseOuter(codeText)->Result.flatMap(expression =>
-    expression->evalUsingExternalBindingsExpression_(bindings)
-  )
+  parse(code)->Result.flatMap(expr => evalUsingBindingsExpression_(expr, bindings, anEnvironment))
 }

 /*
  Evaluates MathJs code and bindings via Reducer and answers the result
 */
-let eval = (codeText: string) => {
-  parse(codeText)->Result.flatMap(expression =>
-    expression->evalUsingExternalBindingsExpression_(defaultBindings)
-  )
-}
-
-type externalBindings = ReducerInterface.ExpressionValue.externalBindings //Js.Dict.t<expressionValue>
-
-let externalBindingsToBindings = (externalBindings: externalBindings): T.bindings => {
-  let keys = Js.Dict.keys(externalBindings)
-  keys->Belt.Array.reduce(defaultBindings, (acc, key) => {
-    let value = Js.Dict.unsafeGet(externalBindings, key)
-    acc->Belt.Map.String.set(key, T.EValue(value))
-  })
-}
-/*
-  Evaluates code with external bindings. External bindings are a record of expression values.
-*/
-let evalUsingExternalBindings = (code: string, externalBindings: externalBindings) => {
-  let bindings = externalBindings->externalBindingsToBindings
-  evalOuterWBindings_(code, bindings)
-}
-
-/*
-  Evaluates code with external bindings. External bindings are a record of expression values.
-  The code is a partial code as if it is cut from a larger code. Therefore all statments are assignments.
-*/
-let evalPartialUsingExternalBindings = (code: string, externalBindings: externalBindings): result<
-  externalBindings,
-  'e,
-> => {
-  let bindings = externalBindings->externalBindingsToBindings
-  let answer = evalPartialUsingExternalBindings_(code, bindings)
-  answer->Result.flatMap(answer =>
-    switch answer {
-    | EvRecord(aRecord) => Ok(aRecord)
-    | _ => RETodo("TODO: External bindings must be returned")->Error
-    }
+let evaluate = (code: string): result<expressionValue, errorValue> => {
+  evaluateUsingOptions(~environment=None, ~externalBindings=None, code)
+}
+let eval = evaluate
+let evaluatePartialUsingExternalBindings = (
+  code: string,
+  externalBindings: ReducerInterface_ExpressionValue.externalBindings,
+  environment: ReducerInterface_ExpressionValue.environment,
+): result<externalBindings, errorValue> => {
+  let rAnswer = evaluateUsingOptions(
+    ~environment=Some(environment),
+    ~externalBindings=Some(externalBindings),
+    code,
  )
+  switch rAnswer {
+  | Ok(EvRecord(externalBindings)) => Ok(externalBindings)
+  | Ok(_) =>
+    Error(Reducer_ErrorValue.RESyntaxError(`Partials must end with an assignment or record`))
+  | Error(err) => err->Error
+  }
 }
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
@ -0,0 +1,45 @@
+module Bindings = Reducer_Expression_Bindings
+module ErrorValue = Reducer_ErrorValue
+module ExpressionT = Reducer_Expression_T
+module ExpressionValue = ReducerInterface.ExpressionValue
+module Result = Belt.Result
+
+type bindings = ExpressionT.bindings
+type context = bindings
+type environment = ExpressionValue.environment
+type errorValue = Reducer_ErrorValue.errorValue
+type expression = ExpressionT.expression
+type expressionValue = ExpressionValue.expressionValue
+type externalBindings = ReducerInterface_ExpressionValue.externalBindings
+type reducerFn = ExpressionT.reducerFn
+
+type expressionWithContext =
+  | ExpressionWithContext(expression, context)
+  | ExpressionNoContext(expression)
+
+let callReducer = (
+  expressionWithContext: expressionWithContext,
+  bindings: bindings,
+  environment: environment,
+  reducer: reducerFn,
+): result<expressionValue, errorValue> =>
+  switch expressionWithContext {
+  | ExpressionNoContext(expr) => reducer(expr, bindings, environment)
+  | ExpressionWithContext(expr, context) => reducer(expr, context, environment)
+  }
+
+let withContext = (expression, context) => ExpressionWithContext(expression, context)
+let noContext = expression => ExpressionNoContext(expression)
+
+let toString = expressionWithContext =>
+  switch expressionWithContext {
+  | ExpressionNoContext(expr) => ExpressionT.toString(expr)
+  | ExpressionWithContext(expr, context) =>
+    `${ExpressionT.toString(expr)} context: ${Bindings.toString(context)}`
+  }
+
+let toStringResult = rExpressionWithContext =>
+  switch rExpressionWithContext {
+  | Ok(expressionWithContext) => `Ok(${toString(expressionWithContext)})`
+  | Error(errorValue) => ErrorValue.errorToString(errorValue)
+  }
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Bindings.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Bindings.res
@ -0,0 +1,85 @@
+module ErrorValue = Reducer_ErrorValue
+module ExpressionT = Reducer_Expression_T
+module ExpressionValue = ReducerInterface.ExpressionValue
+module Result = Belt.Result
+
+type errorValue = Reducer_ErrorValue.errorValue
+type expression = ExpressionT.expression
+type expressionValue = ExpressionValue.expressionValue
+type externalBindings = ReducerInterface_ExpressionValue.externalBindings
+
+let defaultBindings: ExpressionT.bindings = Belt.Map.String.empty
+
+let fromExternalBindings = (externalBindings: externalBindings): ExpressionT.bindings => {
+  let keys = Js.Dict.keys(externalBindings)
+  keys->Belt.Array.reduce(defaultBindings, (acc, key) => {
+    let value = Js.Dict.unsafeGet(externalBindings, key)
+    acc->Belt.Map.String.set(key, value)
+  })
+}
+
+let toExternalBindings = (bindings: ExpressionT.bindings): externalBindings => {
+  let keys = Belt.Map.String.keysToArray(bindings)
+  keys->Belt.Array.reduce(Js.Dict.empty(), (acc, key) => {
+    let value = bindings->Belt.Map.String.getExn(key)
+    Js.Dict.set(acc, key, value)
+    acc
+  })
+}
+
+let fromValue = (aValue: expressionValue) =>
+  switch aValue {
+  | EvRecord(externalBindings) => fromExternalBindings(externalBindings)
+  | _ => defaultBindings
+  }
+
+let externalFromArray = anArray => Js.Dict.fromArray(anArray)
+
+let isMacroName = (fName: string): bool => fName->Js.String2.startsWith("$$")
+
+let rec replaceSymbols = (bindings: ExpressionT.bindings, expression: expression): result<
+  expression,
+  errorValue,
+> =>
+  switch expression {
+  | ExpressionT.EValue(value) =>
+    replaceSymbolOnValue(bindings, value)->Result.map(evValue => evValue->ExpressionT.EValue)
+  | ExpressionT.EList(list) =>
+    switch list {
+    | list{EValue(EvCall(fName)), ..._args} =>
+      switch isMacroName(fName) {
+      // A macro reduces itself so we dont dive in it
+      | true => expression->Ok
+      | false => replaceSymbolsOnExpressionList(bindings, list)
+      }
+    | _ => replaceSymbolsOnExpressionList(bindings, list)
+    }
+  }
+
+and replaceSymbolsOnExpressionList = (bindings, list) => {
+  let racc = list->Belt.List.reduceReverse(Ok(list{}), (racc, each: expression) =>
+    racc->Result.flatMap(acc => {
+      replaceSymbols(bindings, each)->Result.flatMap(newNode => {
+        acc->Belt.List.add(newNode)->Ok
+      })
+    })
+  )
+  racc->Result.map(acc => acc->ExpressionT.EList)
+}
+and replaceSymbolOnValue = (bindings, evValue: expressionValue) =>
+  switch evValue {
+  | EvSymbol(symbol) => Belt.Map.String.getWithDefault(bindings, symbol, evValue)->Ok
+  | EvCall(symbol) => Belt.Map.String.getWithDefault(bindings, symbol, evValue)->checkIfCallable
+  | _ => evValue->Ok
+  }
+and checkIfCallable = (evValue: expressionValue) =>
+  switch evValue {
+  | EvCall(_) | EvLambda(_) => evValue->Ok
+  | _ => ErrorValue.RENotAFunction(ExpressionValue.toString(evValue))->Error
+  }
+
+let toString = (bindings: ExpressionT.bindings) =>
+  bindings->toExternalBindings->ExpressionValue.EvRecord->ExpressionValue.toString
+
+let externalBindingsToString = (externalBindings: externalBindings) =>
+  externalBindings->ExpressionValue.EvRecord->ExpressionValue.toString
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
@ -0,0 +1,66 @@
+module BBindings = Reducer_Expression_Bindings
+module BErrorValue = Reducer_ErrorValue
+module BExpressionT = Reducer_Expression_T
+module BExpressionValue = ReducerInterface.ExpressionValue
+
+type errorValue = BErrorValue.errorValue
+type expression = BExpressionT.expression
+type internalCode = ReducerInterface_ExpressionValue.internalCode
+
+external castExpressionToInternalCode: expression => internalCode = "%identity"
+
+let eArray = anArray => anArray->BExpressionValue.EvArray->BExpressionT.EValue
+
+let eArrayString = anArray => anArray->BExpressionValue.EvArrayString->BExpressionT.EValue
+
+let eBindings = (anArray: array<(string, BExpressionValue.expressionValue)>) =>
+  anArray->Js.Dict.fromArray->EvRecord->BExpressionT.EValue
+
+let eBool = aBool => aBool->BExpressionValue.EvBool->BExpressionT.EValue
+
+let eCall = (name: string): expression => name->BExpressionValue.EvCall->BExpressionT.EValue
+
+let eFunction = (fName: string, lispArgs: list<expression>): expression => {
+  let fn = fName->eCall
+  list{fn, ...lispArgs}->BExpressionT.EList
+}
+
+let eLambda = (
+  parameters: array<string>,
+  context: BExpressionValue.externalBindings,
+  expr: expression,
+) => {
+  // Js.log(`eLambda context ${BBindings.externalBindingsToString(context)}`)
+  BExpressionValue.EvLambda({
+    parameters: parameters,
+    context: context,
+    body: expr->castExpressionToInternalCode,
+  })->BExpressionT.EValue
+}
+
+let eNumber = aNumber => aNumber->BExpressionValue.EvNumber->BExpressionT.EValue
+
+let eRecord = aRecord => aRecord->BExpressionValue.EvRecord->BExpressionT.EValue
+
+let eString = aString => aString->BExpressionValue.EvString->BExpressionT.EValue
+
+let eSymbol = (name: string): expression => name->BExpressionValue.EvSymbol->BExpressionT.EValue
+
+let eList = (list: list<expression>): expression => list->BExpressionT.EList
+
+let eBlock = (exprs: list<expression>): expression => eFunction("$$block", exprs)
+
+let eLetStatement = (symbol: string, valueExpression: expression): expression =>
+  eFunction("$let", list{eSymbol(symbol), valueExpression})
+
+let eBindStatement = (bindingExpr: expression, letStatement: expression): expression =>
+  eFunction("$$bindStatement", list{bindingExpr, letStatement})
+
+let eBindStatementDefault = (letStatement: expression): expression =>
+  eFunction("$$bindStatement", list{letStatement})
+
+let eBindExpression = (bindingExpr: expression, expression: expression): expression =>
+  eFunction("$$bindExpression", list{bindingExpr, expression})
+
+let eBindExpressionDefault = (expression: expression): expression =>
+  eFunction("$$bindExpression", list{expression})
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
@ -0,0 +1,60 @@
+module Bindings = Reducer_Expression_Bindings
+module ErrorValue = Reducer_ErrorValue
+module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
+module ExpressionT = Reducer_Expression_T
+module ExpressionValue = ReducerInterface.ExpressionValue
+module Result = Belt.Result
+
+type environment = ReducerInterface_ExpressionValue.environment
+type expression = ExpressionT.expression
+type expressionValue = ReducerInterface_ExpressionValue.expressionValue
+type externalBindings = ReducerInterface_ExpressionValue.externalBindings
+type internalCode = ReducerInterface_ExpressionValue.internalCode
+
+external castInternalCodeToExpression: internalCode => expression = "%identity"
+
+let checkArity = (lambdaValue: ExpressionValue.lambdaValue, args: list<expressionValue>) => {
+  let argsLength = Belt.List.length(args)
+  let parametersLength = Js.Array2.length(lambdaValue.parameters)
+  if argsLength !== parametersLength {
+    ErrorValue.REArityError(None, parametersLength, argsLength)->Error
+  } else {
+    args->Ok
+  }
+}
+
+let checkIfReduced = (args: list<expressionValue>) =>
+  args->Belt.List.reduceReverse(Ok(list{}), (rAcc, arg) =>
+    rAcc->Result.flatMap(acc =>
+      switch arg {
+      | EvSymbol(symbol) => ErrorValue.RESymbolNotFound(symbol)->Error
+      | _ => list{arg, ...acc}->Ok
+      }
+    )
+  )
+
+let applyParametersToLambda = (
+  lambdaValue: ExpressionValue.lambdaValue,
+  args,
+  environment,
+  reducer: ExpressionT.reducerFn,
+): result<expressionValue, 'e> => {
+  checkArity(lambdaValue, args)->Result.flatMap(args =>
+    checkIfReduced(args)->Result.flatMap(args => {
+      let expr = castInternalCodeToExpression(lambdaValue.body)
+      let parameterList = lambdaValue.parameters->Belt.List.fromArray
+      let zippedParameterList = parameterList->Belt.List.zip(args)
+      let bindings = Belt.List.reduce(
+        zippedParameterList,
+        lambdaValue.context->Bindings.fromExternalBindings,
+        (acc, (variable, variableValue)) => acc->Belt.Map.String.set(variable, variableValue),
+      )
+      let newExpression = ExpressionBuilder.eBlock(list{expr})
+      reducer(newExpression, bindings, environment)
+    })
+  )
+}
+
+let doLambdaCall = (lambdaValue: ExpressionValue.lambdaValue, args, environment, reducer) => {
+  applyParametersToLambda(lambdaValue, args, environment, reducer)
+}
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Macro.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Macro.res
@ -0,0 +1,44 @@
+module ExpressionT = Reducer_Expression_T
+module ExpressionValue = ReducerInterface.ExpressionValue
+module ExpressionWithContext = Reducer_ExpressionWithContext
+module Result = Belt.Result
+
+type environment = ExpressionValue.environment
+type expression = ExpressionT.expression
+type expressionValue = ExpressionValue.expressionValue
+type expressionWithContext = ExpressionWithContext.expressionWithContext
+
+let expandMacroCall = (
+  macroExpression: expression,
+  bindings: ExpressionT.bindings,
+  environment: environment,
+  reduceExpression: ExpressionT.reducerFn,
+): result<expressionWithContext, 'e> =>
+  Reducer_Dispatch_BuiltInMacros.dispatchMacroCall(
+    macroExpression,
+    bindings,
+    environment,
+    reduceExpression,
+  )
+
+let doMacroCall = (
+  macroExpression: expression,
+  bindings: ExpressionT.bindings,
+  environment: environment,
+  reduceExpression: ExpressionT.reducerFn,
+): result<expressionValue, 'e> =>
+  expandMacroCall(
+    macroExpression,
+    bindings,
+    environment,
+    reduceExpression,
+  )->Result.flatMap(expressionWithContext =>
+    ExpressionWithContext.callReducer(
+      expressionWithContext,
+      bindings,
+      environment,
+      reduceExpression,
+    )
+  )
+
+let isMacroName = (fName: string): bool => fName->Js.String2.startsWith("$$")
--- 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 +1,3 @@
-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
@ -8,8 +6,51 @@ open ReducerInterface.ExpressionValue
  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.
 */
+module Extra = Reducer_Extra
+module ExpressionValue = ReducerInterface.ExpressionValue
+
+type expressionValue = ExpressionValue.expressionValue
+type environment = ExpressionValue.environment
+
 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>
+and bindings = Belt.Map.String.t<expressionValue>
+
+type reducerFn = (
+  expression,
+  bindings,
+  environment,
+) => result<expressionValue, Reducer_ErrorValue.errorValue>
+
+/*
+  Converts the expression to String
+*/
+let rec toString = expression =>
+  switch expression {
+  | EList(aList) =>
+    `(${Belt.List.map(aList, aValue => toString(aValue))
+      ->Extra.List.interperse(" ")
+      ->Belt.List.toArray
+      ->Js.String.concatMany("")})`
+  | EValue(aValue) => ExpressionValue.toString(aValue)
+  }
+
+let toStringResult = codeResult =>
+  switch codeResult {
+  | Ok(a) => `Ok(${toString(a)})`
+  | Error(m) => `Error(${Reducer_ErrorValue.errorToString(m)})`
+  }
+
+let inspect = (expr: expression): expression => {
+  Js.log(toString(expr))
+  expr
+}
+
+let inspectResult = (r: result<expression, Reducer_ErrorValue.errorValue>): result<
+  expression,
+  Reducer_ErrorValue.errorValue,
+> => {
+  Js.log(toStringResult(r))
+  r
+}
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Js/Reducer_Js_Gate.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Js/Reducer_Js_Gate.res
@ -8,11 +8,10 @@ external castString: unit => string = "%identity"
 /*
  As JavaScript returns us any type, we need to type check and cast type propertype before using it
 */
-let jsToEv = (jsValue): result<expressionValue, errorValue> => {
+let jsToEv = (jsValue): result<expressionValue, errorValue> =>
  switch Js.typeof(jsValue) {
  | "boolean" => jsValue->castBool->EvBool->Ok
  | "number" => jsValue->castNumber->EvNumber->Ok
  | "string" => jsValue->castString->EvString->Ok
  | other => RETodo(`Unhandled MathJs literal type: ${Js.String.make(other)}`)->Error
  }
-}
--- 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
@ -11,11 +11,10 @@ type block = {"node": node}
 type blockNode = {...node, "blocks": array<block>}
 //conditionalNode
 type constantNode = {...node, "value": unit}
-//functionAssignmentNode
+type functionAssignmentNode = {...node, "name": string, "params": array<string>, "expr": node}
 type indexNode = {...node, "dimensions": array<node>}
 type objectNode = {...node, "properties": Js.Dict.t<node>}
 type accessorNode = {...node, "object": node, "index": indexNode, "name": string}
-
 type parenthesisNode = {...node, "content": node}
 //rangeNode
 //relationalNode
@ -33,6 +32,7 @@ external castAssignmentNodeWAccessor: node => assignmentNodeWAccessor = "%identi
 external castAssignmentNodeWIndex: node => assignmentNodeWIndex = "%identity"
 external castBlockNode: node => blockNode = "%identity"
 external castConstantNode: node => constantNode = "%identity"
+external castFunctionAssignmentNode: node => functionAssignmentNode = "%identity"
 external castFunctionNode: node => functionNode = "%identity"
 external castIndexNode: node => indexNode = "%identity"
 external castObjectNode: node => objectNode = "%identity"
@ -59,6 +59,7 @@ type mathJsNode =
  | MjAssignmentNode(assignmentNode)
  | MjBlockNode(blockNode)
  | MjConstantNode(constantNode)
+  | MjFunctionAssignmentNode(functionAssignmentNode)
  | MjFunctionNode(functionNode)
  | MjIndexNode(indexNode)
  | MjObjectNode(objectNode)
@ -82,6 +83,7 @@ let castNodeType = (node: node) => {
  | "AssignmentNode" => node->decideAssignmentNode
  | "BlockNode" => node->castBlockNode->MjBlockNode->Ok
  | "ConstantNode" => node->castConstantNode->MjConstantNode->Ok
+  | "FunctionAssignmentNode" => node->castFunctionAssignmentNode->MjFunctionAssignmentNode->Ok
  | "FunctionNode" => node->castFunctionNode->MjFunctionNode->Ok
  | "IndexNode" => node->castIndexNode->MjIndexNode->Ok
  | "ObjectNode" => node->castObjectNode->MjObjectNode->Ok
@ -118,6 +120,10 @@ let rec toString = (mathJsNode: mathJsNode): string => {
    ->Extra.Array.interperse(", ")
    ->Js.String.concatMany("")

+  let toStringFunctionAssignmentNode = (faNode: functionAssignmentNode): string => {
+    let paramNames = Js.Array2.toString(faNode["params"])
+    `${faNode["name"]} = (${paramNames}) => ${toStringMathJsNode(faNode["expr"])}`
+  }
  let toStringFunctionNode = (fnode: functionNode): string =>
    `${fnode->nameOfFunctionNode}(${fnode["args"]->toStringNodeArray})`

@ -152,6 +158,7 @@ let rec toString = (mathJsNode: mathJsNode): string => {
    `${aNode["object"]->toStringSymbolNode} = ${aNode["value"]->toStringMathJsNode}`
  | MjBlockNode(bNode) => `{${bNode["blocks"]->toStringBlocks}}`
  | MjConstantNode(cNode) => cNode["value"]->toStringValue
+  | MjFunctionAssignmentNode(faNode) => faNode->toStringFunctionAssignmentNode
  | MjFunctionNode(fNode) => fNode->toStringFunctionNode
  | MjIndexNode(iNode) => iNode->toStringIndexNode
  | MjObjectNode(oNode) => oNode->toStringObjectNode
--- 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
@ -1,45 +1,35 @@
+/* * WARNING. DO NOT EDIT, BEAUTIFY, COMMENT ON OR REFACTOR THIS CODE. 
+We will stop using MathJs parser and
+this whole file will go to trash
+**/
 module ErrorValue = Reducer_ErrorValue
-module ExpressionValue = ReducerInterface.ExpressionValue
+module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
 module ExpressionT = Reducer_Expression_T
+module ExpressionValue = ReducerInterface.ExpressionValue
 module JavaScript = Reducer_Js
 module Parse = Reducer_MathJs_Parse
 module Result = Belt.Result

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

-let passToFunction = (fName: string, rLispArgs): result<expression, errorValue> => {
-  let toEvCallValue = (name: string): expression => name->ExpressionValue.EvCall->ExpressionT.EValue
+let blockToNode = block => block["node"]

-  let fn = fName->toEvCallValue
-  rLispArgs->Result.flatMap(lispArgs => list{fn, ...lispArgs}->ExpressionT.EList->Ok)
-}
-
-type blockTag =
-  | ImportVariablesStatement
-  | ExportVariablesExpression
-type tagOrNode =
-  | BlockTag(blockTag)
-  | BlockNode(Parse.node)
-
-let toTagOrNode = block => BlockNode(block["node"])
-
-let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
+let rec fromInnerNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
  Parse.castNodeType(mathJsNode)->Result.flatMap(typedMathJsNode => {
    let fromNodeList = (nodeList: list<Parse.node>): result<list<expression>, 'e> =>
      Belt.List.reduceReverse(nodeList, Ok(list{}), (racc, currNode) =>
        racc->Result.flatMap(acc =>
-          fromNode(currNode)->Result.map(currCode => list{currCode, ...acc})
+          fromInnerNode(currNode)->Result.map(currCode => list{currCode, ...acc})
        )
      )

-    let toEvSymbolValue = (name: string): expression =>
-      name->ExpressionValue.EvSymbol->ExpressionT.EValue
-
    let caseFunctionNode = fNode => {
-      let lispArgs = fNode["args"]->Belt.List.fromArray->fromNodeList
-      passToFunction(fNode->Parse.nameOfFunctionNode, lispArgs)
+      let rLispArgs = fNode["args"]->Belt.List.fromArray->fromNodeList
+      rLispArgs->Result.map(lispArgs =>
+        ExpressionBuilder.eFunction(fNode->Parse.nameOfFunctionNode, lispArgs)
+      )
    }

    let caseObjectNode = oNode => {
@ -49,19 +39,16 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
          (key: string, value: Parse.node),
        ) =>
          racc->Result.flatMap(acc =>
-            fromNode(value)->Result.map(valueExpression => {
+            fromInnerNode(value)->Result.map(valueExpression => {
              let entryCode =
-                list{
-                  key->ExpressionValue.EvString->ExpressionT.EValue,
-                  valueExpression,
-                }->ExpressionT.EList
+                list{ExpressionBuilder.eString(key), valueExpression}->ExpressionT.EList
              list{entryCode, ...acc}
            })
          )
        )
        rargs->Result.flatMap(args =>
-          passToFunction("$constructRecord", list{ExpressionT.EList(args)}->Ok)
-        ) // $consturctRecord gets a single argument: List of key-value paiers
+          ExpressionBuilder.eFunction("$constructRecord", list{ExpressionT.EList(args)})->Ok
+        ) // $constructRecord gets a single argument: List of key-value paiers
      }

      oNode["properties"]->Js.Dict.entries->Belt.List.fromArray->fromObjectEntries
@ -73,7 +60,7 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
        Ok(list{}),
        (racc, currentPropertyMathJsNode) =>
          racc->Result.flatMap(acc =>
-            fromNode(currentPropertyMathJsNode)->Result.map(propertyCode => list{
+            fromInnerNode(currentPropertyMathJsNode)->Result.map(propertyCode => list{
              propertyCode,
              ...acc,
            })
@ -84,18 +71,41 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>

    let caseAccessorNode = (objectNode, indexNode) => {
      caseIndexNode(indexNode)->Result.flatMap(indexCode => {
-        fromNode(objectNode)->Result.flatMap(objectCode =>
-          passToFunction("$atIndex", list{objectCode, indexCode}->Ok)
+        fromInnerNode(objectNode)->Result.flatMap(objectCode =>
+          ExpressionBuilder.eFunction("$atIndex", list{objectCode, indexCode})->Ok
        )
      })
    }

+    let caseBlock = (nodesArray: array<Parse.node>): result<expression, errorValue> => {
+      let rStatements: result<list<expression>, 'a> =
+        nodesArray
+        ->Belt.List.fromArray
+        ->Belt.List.reduceReverse(Ok(list{}), (racc, currNode) =>
+          racc->Result.flatMap(acc =>
+            fromInnerNode(currNode)->Result.map(currCode => list{currCode, ...acc})
+          )
+        )
+      rStatements->Result.map(statements => ExpressionBuilder.eBlock(statements))
+    }
+
    let caseAssignmentNode = aNode => {
-      let symbol = aNode["object"]["name"]->toEvSymbolValue
-      let rValueExpression = fromNode(aNode["value"])
+      let symbolName = aNode["object"]["name"]
+      let rValueExpression = fromInnerNode(aNode["value"])
+      rValueExpression->Result.map(valueExpression =>
+        ExpressionBuilder.eLetStatement(symbolName, valueExpression)
+      )
+    }
+
+    let caseFunctionAssignmentNode = faNode => {
+      let symbol = faNode["name"]->ExpressionBuilder.eSymbol
+      let rValueExpression = fromInnerNode(faNode["expr"])
+
      rValueExpression->Result.flatMap(valueExpression => {
-        let lispArgs = list{symbol, valueExpression}->Ok
-        passToFunction("$let", lispArgs)
+        let lispParams = ExpressionBuilder.eArrayString(faNode["params"])
+        let valueBlock = ExpressionBuilder.eBlock(list{valueExpression})
+        let lambda = ExpressionBuilder.eFunction("$$lambda", list{lispParams, valueBlock})
+        ExpressionBuilder.eFunction("$let", list{symbol, lambda})->Ok
      })
    }

@ -108,88 +118,22 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
    | MjArrayNode(aNode) => caseArrayNode(aNode)
    | MjAssignmentNode(aNode) => caseAssignmentNode(aNode)
    | MjSymbolNode(sNode) => {
-        let expr: expression = toEvSymbolValue(sNode["name"])
+        let expr: expression = ExpressionBuilder.eSymbol(sNode["name"])
        let rExpr: result<expression, errorValue> = expr->Ok
        rExpr
      }
-    | MjBlockNode(bNode) => bNode["blocks"]->Belt.Array.map(toTagOrNode)->caseTagOrNodes
+    | MjBlockNode(bNode) => bNode["blocks"]->Js.Array2.map(blockToNode)->caseBlock
    | MjConstantNode(cNode) =>
      cNode["value"]->JavaScript.Gate.jsToEv->Result.flatMap(v => v->ExpressionT.EValue->Ok)
+    | MjFunctionAssignmentNode(faNode) => caseFunctionAssignmentNode(faNode)
    | MjFunctionNode(fNode) => fNode->caseFunctionNode
    | MjIndexNode(iNode) => caseIndexNode(iNode)
    | MjObjectNode(oNode) => caseObjectNode(oNode)
    | MjOperatorNode(opNode) => opNode->Parse.castOperatorNodeToFunctionNode->caseFunctionNode
-    | MjParenthesisNode(pNode) => pNode["content"]->fromNode
+    | MjParenthesisNode(pNode) => pNode["content"]->fromInnerNode
    }
    rFinalExpression
  })
-and caseTagOrNodes = (tagOrNodes): result<expression, errorValue> => {
-  let initialBindings = passToFunction("$$bindings", list{}->Ok)
-  let lastIndex = Belt.Array.length(tagOrNodes) - 1
-  tagOrNodes->Belt.Array.reduceWithIndex(initialBindings, (rPreviousBindings, tagOrNode, i) => {
-    rPreviousBindings->Result.flatMap(previousBindings => {
-      let rStatement: result<expression, errorValue> = switch tagOrNode {
-      | BlockNode(node) => fromNode(node)
-      | BlockTag(tag) =>
-        switch tag {
-        | ImportVariablesStatement => passToFunction("$importVariablesStatement", list{}->Ok)
-        | ExportVariablesExpression => passToFunction("$exportVariablesExpression", list{}->Ok)
-        }
-      }

-      let bindName = if i == lastIndex {
-        "$$bindExpression"
-      } else {
-        "$$bindStatement"
-      }
-
-      rStatement->Result.flatMap((statement: expression) => {
-        let lispArgs = list{previousBindings, statement}->Ok
-        passToFunction(bindName, lispArgs)
-      })
-    })
-  })
-}
-
-let fromPartialNode = (mathJsNode: Parse.node): result<expression, errorValue> => {
-  Parse.castNodeType(mathJsNode)->Result.flatMap(typedMathJsNode => {
-    let casePartialBlockNode = (bNode: Parse.blockNode) => {
-      let blocksOrTags = bNode["blocks"]->Belt.Array.map(toTagOrNode)
-      let completed = Js.Array2.concat(blocksOrTags, [BlockTag(ExportVariablesExpression)])
-      completed->caseTagOrNodes
-    }
-
-    let casePartialExpression = (node: Parse.node) => {
-      let completed = [BlockNode(node), BlockTag(ExportVariablesExpression)]
-
-      completed->caseTagOrNodes
-    }
-
-    let rFinalExpression: result<expression, errorValue> = switch typedMathJsNode {
-    | MjBlockNode(bNode) => casePartialBlockNode(bNode)
-    | _ => casePartialExpression(mathJsNode)
-    }
-    rFinalExpression
-  })
-}
-
-let fromOuterNode = (mathJsNode: Parse.node): result<expression, errorValue> => {
-  Parse.castNodeType(mathJsNode)->Result.flatMap(typedMathJsNode => {
-    let casePartialBlockNode = (bNode: Parse.blockNode) => {
-      let blocksOrTags = bNode["blocks"]->Belt.Array.map(toTagOrNode)
-      let completed = blocksOrTags
-      completed->caseTagOrNodes
-    }
-
-    let casePartialExpression = (node: Parse.node) => {
-      let completed = [BlockNode(node)]
-      completed->caseTagOrNodes
-    }
-
-    let rFinalExpression: result<expression, errorValue> = switch typedMathJsNode {
-    | MjBlockNode(bNode) => casePartialBlockNode(bNode)
-    | _ => casePartialExpression(mathJsNode)
-    }
-    rFinalExpression
-  })
-}
+let fromNode = (node: Parse.node): result<expression, errorValue> =>
+  fromInnerNode(node)->Result.map(expr => ExpressionBuilder.eBlock(list{expr}))
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
@ -5,37 +5,50 @@
 module Extra_Array = Reducer_Extra_Array
 module ErrorValue = Reducer_ErrorValue

+@genType.opaque
+type internalCode = Object
+
@genType
 type rec expressionValue =
  | EvArray(array<expressionValue>)
+  | EvArrayString(array<string>)
  | EvBool(bool)
  | EvCall(string) // External function call
  | EvDistribution(DistributionTypes.genericDist)
+  | EvLambda(lambdaValue)
  | EvNumber(float)
-  | EvRecord(Js.Dict.t<expressionValue>)
+  | EvRecord(record)
  | EvString(string)
  | EvSymbol(string)
+and record = Js.Dict.t<expressionValue>
+and externalBindings = record
+and lambdaValue = {
+  parameters: array<string>,
+  context: externalBindings,
+  body: internalCode,
+}

@genType
-type externalBindings = Js.Dict.t<expressionValue>
+let defaultExternalBindings: externalBindings = Js.Dict.empty()

 type functionCall = (string, array<expressionValue>)

 let rec toString = aValue =>
  switch aValue {
+  | EvArray(anArray) => {
+      let args = anArray->Js.Array2.map(each => toString(each))->Js.Array2.toString
+      `[${args}]`
+    }
+  | EvArrayString(anArray) => {
+      let args = anArray->Js.Array2.toString
+      `[${args}]`
+    }
  | EvBool(aBool) => Js.String.make(aBool)
  | EvCall(fName) => `:${fName}`
+  | EvLambda(lambdaValue) => `lambda(${Js.Array2.toString(lambdaValue.parameters)}=>internal code)`
  | 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("")
-      `[${args}]`
-    }
  | EvRecord(aRecord) => aRecord->toStringRecord
  | EvDistribution(dist) => GenericDist.toString(dist)
  }
@ -43,26 +56,27 @@ and toStringRecord = aRecord => {
  let pairs =
    aRecord
    ->Js.Dict.entries
-    ->Belt.Array.map(((eachKey, eachValue)) => `${eachKey}: ${toString(eachValue)}`)
-    ->Extra_Array.interperse(", ")
-    ->Js.String.concatMany("")
+    ->Js.Array2.map(((eachKey, eachValue)) => `${eachKey}: ${toString(eachValue)}`)
+    ->Js.Array2.toString
  `{${pairs}}`
 }

 let toStringWithType = aValue =>
  switch aValue {
+  | EvArray(_) => `Array::${toString(aValue)}`
+  | EvArrayString(_) => `ArrayString::${toString(aValue)}`
  | EvBool(_) => `Bool::${toString(aValue)}`
  | EvCall(_) => `Call::${toString(aValue)}`
+  | EvDistribution(_) => `Distribution::${toString(aValue)}`
+  | EvLambda(_) => `Lambda::${toString(aValue)}`
  | EvNumber(_) => `Number::${toString(aValue)}`
+  | EvRecord(_) => `Record::${toString(aValue)}`
  | EvString(_) => `String::${toString(aValue)}`
  | EvSymbol(_) => `Symbol::${toString(aValue)}`
-  | EvArray(_) => `Array::${toString(aValue)}`
-  | EvRecord(_) => `Record::${toString(aValue)}`
-  | EvDistribution(_) => `Distribution::${toString(aValue)}`
  }

 let argsToString = (args: array<expressionValue>): string => {
-  args->Belt.Array.map(arg => arg->toString)->Extra_Array.interperse(", ")->Js.String.concatMany("")
+  args->Js.Array2.map(arg => arg->toString)->Js.Array2.toString
 }

 let toStringFunctionCall = ((fn, args)): string => `${fn}(${argsToString(args)})`
@ -78,3 +92,9 @@ let toStringResultRecord = x =>
  | Ok(a) => `Ok(${toStringRecord(a)})`
  | Error(m) => `Error(${ErrorValue.errorToString(m)})`
  }
+
+@genType
+type environment = DistributionOperation.env
+
+@genType
+let defaultEnvironment: environment = DistributionOperation.defaultEnv
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalLibrary.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalLibrary.res
@ -14,8 +14,13 @@ type expressionValue = ExpressionValue.expressionValue
  Map external calls of Reducer
 */

-let dispatch = (call: ExpressionValue.functionCall, chain): result<expressionValue, 'e> =>
-  ReducerInterface_GenericDistribution.dispatch(call) |> E.O.default(chain(call))
+let dispatch = (call: ExpressionValue.functionCall, environment, chain): result<
+  expressionValue,
+  'e,
+> =>
+  ReducerInterface_GenericDistribution.dispatch(call, environment) |> E.O.default(
+    chain(call, environment),
+  )
 /*
 If your dispatch is too big you can divide it into smaller dispatches and pass the call so that it gets called finally.

--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.res
@ -1,12 +1,12 @@
 module ExpressionValue = ReducerInterface_ExpressionValue
 type expressionValue = ReducerInterface_ExpressionValue.expressionValue

-let runGenericOperation = DistributionOperation.run(
-  ~env={
-    sampleCount: MagicNumbers.Environment.defaultSampleCount,
-    xyPointLength: MagicNumbers.Environment.defaultXYPointLength,
-  },
-)
+let defaultEnv: DistributionOperation.env = {
+  sampleCount: MagicNumbers.Environment.defaultSampleCount,
+  xyPointLength: MagicNumbers.Environment.defaultXYPointLength,
+}
+
+let runGenericOperation = DistributionOperation.run(~env=defaultEnv)

 module Helpers = {
  let arithmeticMap = r =>
@ -28,14 +28,13 @@ module Helpers = {
  let catchAndConvertTwoArgsToDists = (args: array<expressionValue>): option<(
    DistributionTypes.genericDist,
    DistributionTypes.genericDist,
-  )> => {
+  )> =>
    switch args {
    | [EvDistribution(a), EvDistribution(b)] => Some((a, b))
    | [EvNumber(a), EvDistribution(b)] => Some((GenericDist.fromFloat(a), b))
    | [EvDistribution(a), EvNumber(b)] => Some((a, GenericDist.fromFloat(b)))
    | _ => None
    }
-  }

  let toFloatFn = (
    fnCall: DistributionTypes.DistributionOperation.toFloat,
@ -120,7 +119,7 @@ module Helpers = {
    mixtureWithGivenWeights(distributions, weights)
  }

-  let mixture = (args: array<expressionValue>): DistributionOperation.outputType => {
+  let mixture = (args: array<expressionValue>): DistributionOperation.outputType =>
    switch E.A.last(args) {
    | Some(EvArray(b)) => {
        let weights = parseNumberArray(b)
@ -140,7 +139,6 @@ module Helpers = {
      }
    | _ => GenDistError(ArgumentError("Last argument of mx must be array or distribution"))
    }
-  }
 }

 module SymbolicConstructors = {
@ -176,7 +174,7 @@ module SymbolicConstructors = {
    }
 }

-let dispatchToGenericOutput = (call: ExpressionValue.functionCall): option<
+let dispatchToGenericOutput = (call: ExpressionValue.functionCall, _environment): option<
  DistributionOperation.outputType,
 > => {
  let (fnName, args) = call
@ -297,6 +295,6 @@ let genericOutputToReducerValue = (o: DistributionOperation.outputType): result<
  | GenDistError(err) => Error(REDistributionError(err))
  }

-let dispatch = call => {
-  dispatchToGenericOutput(call)->E.O2.fmap(genericOutputToReducerValue)
+let dispatch = (call, environment) => {
+  dispatchToGenericOutput(call, environment)->E.O2.fmap(genericOutputToReducerValue)
 }
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.resi
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.resi
@ -1,3 +1,5 @@
-let dispatch: ReducerInterface_ExpressionValue.functionCall => option<
-  result<ReducerInterface_ExpressionValue.expressionValue, Reducer_ErrorValue.errorValue>,
->
+let defaultEnv: DistributionOperation.env
+let dispatch: (
+  ReducerInterface_ExpressionValue.functionCall,
+  ReducerInterface_ExpressionValue.environment,
+) => option<result<ReducerInterface_ExpressionValue.expressionValue, Reducer_ErrorValue.errorValue>>
--- a/packages/squiggle-lang/src/rescript/TypescriptInterface.res
+++ b/packages/squiggle-lang/src/rescript/TypescriptInterface.res
@ -38,7 +38,7 @@ let makeSampleSetDist = SampleSetDist.make
 let evaluate = Reducer.evaluate

@genType
-let evaluateUsingExternalBindings = Reducer.evaluateUsingExternalBindings
+let evaluateUsingOptions = Reducer.evaluateUsingOptions

@genType
 let evaluatePartialUsingExternalBindings = Reducer.evaluatePartialUsingExternalBindings
@ -49,6 +49,9 @@ type externalBindings = Reducer.externalBindings
@genType
 type expressionValue = ReducerInterface_ExpressionValue.expressionValue

+@genType
+type recordEV = ReducerInterface_ExpressionValue.record
+
@genType
 type errorValue = Reducer_ErrorValue.errorValue

@ -69,3 +72,15 @@ let errorValueToString = Reducer_ErrorValue.errorToString

@genType
 let distributionErrorToString = DistributionTypes.Error.toString
+
+@genType
+type lambdaValue = ReducerInterface_ExpressionValue.lambdaValue
+
+@genType
+let defaultSamplingEnv = ReducerInterface_GenericDistribution.defaultEnv
+
+@genType
+type environment = ReducerInterface_ExpressionValue.environment
+
+@genType
+let defaultEnvironment = ReducerInterface_ExpressionValue.defaultEnvironment