Merge pull request #628 from quantified-uncertainty/reducer-type-grammar

Reducer type grammar - preview release

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_Parse_test.res

@@ -1,26 +1,5 @@
-module Parse = Reducer_Peggy_Parse
-module Result = Belt.Result
-
 open Jest
-open Expect
+open Reducer_Peggy_TestHelpers
-
-let expectParseToBe = (expr, answer) =>
-  Parse.parse(expr)->Parse.toStringResult->expect->toBe(answer)
-
-let testParse = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
-
-module MySkip = {
-  let testParse = (expr, answer) => Skip.test(expr, () => expectParseToBe(expr, answer))
-
-  let testDescriptionParse = (desc, expr, answer) =>
-    Skip.test(desc, () => expectParseToBe(expr, answer))
-}
-
-module MyOnly = {
-  let testParse = (expr, answer) => Only.test(expr, () => expectParseToBe(expr, answer))
-  let testDescriptionParse = (desc, expr, answer) =>
-    Only.test(desc, () => expectParseToBe(expr, answer))
-}
 
 describe("Peggy parse", () => {
   describe("float", () => {

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_Parse_type_test.res

@@ -0,0 +1,79 @@
+open Jest
+open Reducer_Peggy_TestHelpers
+
+describe("Peggy parse type", () => {
+  describe("type of", () => {
+    testParse("p: number", "{(::$_typeOf_$ :p #number)}")
+  })
+  describe("type alias", () => {
+    testParse("type index=number", "{(::$_typeAlias_$ #index #number)}")
+  })
+  describe("type or", () => {
+    testParse(
+      "answer: number|string",
+      "{(::$_typeOf_$ :answer (::$_typeOr_$ (::$_constructArray_$ (#number #string))))}",
+    )
+  })
+  describe("type function", () => {
+    testParse(
+      "f: number=>number=>number",
+      "{(::$_typeOf_$ :f (::$_typeFunction_$ (::$_constructArray_$ (#number #number #number))))}",
+    )
+  })
+  describe("high priority modifier", () => {
+    testParse(
+      "answer: number<-min<-max(100)|string",
+      "{(::$_typeOf_$ :answer (::$_typeOr_$ (::$_constructArray_$ ((::$_typeModifier_max_$ (::$_typeModifier_min_$ #number) 100) #string))))}",
+    )
+    testParse(
+      "answer: number<-memberOf([1,3,5])",
+      "{(::$_typeOf_$ :answer (::$_typeModifier_memberOf_$ #number (::$_constructArray_$ (1 3 5))))}",
+    )
+  })
+  describe("low priority modifier", () => {
+    testParse(
+      "answer: number | string $ opaque",
+      "{(::$_typeOf_$ :answer (::$_typeModifier_opaque_$ (::$_typeOr_$ (::$_constructArray_$ (#number #string)))))}",
+    )
+  })
+  describe("type array", () => {
+    testParse("answer: [number]", "{(::$_typeOf_$ :answer (::$_typeArray_$ #number))}")
+  })
+  describe("type record", () => {
+    testParse(
+      "answer: {a: number, b: string}",
+      "{(::$_typeOf_$ :answer (::$_typeRecord_$ (::$_constructRecord_$ ('a': #number 'b': #string))))}",
+    )
+  })
+  describe("type constructor", () => {
+    testParse(
+      "answer: Age(number)",
+      "{(::$_typeOf_$ :answer (::$_typeConstructor_$ #Age (::$_constructArray_$ (#number))))}",
+    )
+    testParse(
+      "answer: Complex(number, number)",
+      "{(::$_typeOf_$ :answer (::$_typeConstructor_$ #Complex (::$_constructArray_$ (#number #number))))}",
+    )
+    testParse(
+      "answer: Person({age: number, name: string})",
+      "{(::$_typeOf_$ :answer (::$_typeConstructor_$ #Person (::$_constructArray_$ ((::$_typeRecord_$ (::$_constructRecord_$ ('age': #number 'name': #string)))))))}",
+    )
+    testParse(
+      "weekend: Saturday | Sunday",
+      "{(::$_typeOf_$ :weekend (::$_typeOr_$ (::$_constructArray_$ ((::$_typeConstructor_$ #Saturday (::$_constructArray_$ ())) (::$_typeConstructor_$ #Sunday (::$_constructArray_$ ()))))))}",
+    )
+  })
+  describe("type paranthesis", () => {
+    //$ is introduced to avoid paranthesis
+    testParse(
+      "answer: (number|string)<-opaque",
+      "{(::$_typeOf_$ :answer (::$_typeModifier_opaque_$ (::$_typeOr_$ (::$_constructArray_$ (#number #string)))))}",
+    )
+  })
+  describe("squiggle expressions in type modifiers", () => {
+    testParse(
+      "odds1 = [1,3,5]; odds2 = [7, 9]; type odds = number<-memberOf(concat(odds1, odds2))",
+      "{:odds1 = {(::$_constructArray_$ (1 3 5))}; :odds2 = {(::$_constructArray_$ (7 9))}; (::$_typeAlias_$ #odds (::$_typeModifier_memberOf_$ #number (::concat :odds1 :odds2)))}",
+    )
+  })
+})

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_TestHelpers.res

@@ -0,0 +1,46 @@
+module Expression = Reducer_Expression
+module ExpressionT = Reducer_Expression_T
+module ExpressionValue = ReducerInterface_ExpressionValue
+module Parse = Reducer_Peggy_Parse
+module Result = Belt.Result
+module ToExpression = Reducer_Peggy_ToExpression
+
+open Jest
+open Expect
+
+let expectParseToBe = (expr, answer) =>
+  Parse.parse(expr)->Parse.toStringResult->expect->toBe(answer)
+
+let testParse = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
+
+let expectToExpressionToBe = (expr, answer, ~v="_", ()) => {
+  let rExpr = Parse.parse(expr)->Result.map(ToExpression.fromNode)
+  let a1 = rExpr->ExpressionT.toStringResultOkless
+
+  if v == "_" {
+    a1->expect->toBe(answer)
+  } else {
+    let a2 =
+      rExpr
+      ->Result.flatMap(expr =>
+        Expression.reduceExpression(expr, Belt.Map.String.empty, ExpressionValue.defaultEnvironment)
+      )
+      ->ExpressionValue.toStringResultOkless
+    (a1, a2)->expect->toEqual((answer, v))
+  }
+}
+
+let testToExpression = (expr, answer, ~v="_", ()) =>
+  test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
+
+module MyOnly = {
+  let testParse = (expr, answer) => Only.test(expr, () => expectParseToBe(expr, answer))
+  let testToExpression = (expr, answer, ~v="_", ()) =>
+    Only.test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
+}
+
+module MySkip = {
+  let testParse = (expr, answer) => Skip.test(expr, () => expectParseToBe(expr, answer))
+  let testToExpression = (expr, answer, ~v="_", ()) =>
+    Skip.test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
+}

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_ToExpression_test.res

@@ -1,41 +1,5 @@
-module Expression = Reducer_Expression
-module ExpressionT = Reducer_Expression_T
-module ExpressionValue = ReducerInterface_ExpressionValue
-module Parse = Reducer_Peggy_Parse
-module ToExpression = Reducer_Peggy_ToExpression
-module Result = Belt.Result
-
 open Jest
-open Expect
+open Reducer_Peggy_TestHelpers
-
-let expectToExpressionToBe = (expr, answer, ~v="_", ()) => {
-  let rExpr = Parse.parse(expr)->Result.map(ToExpression.fromNode)
-  let a1 = rExpr->ExpressionT.toStringResultOkless
-  if v == "_" {
-    a1->expect->toBe(answer)
-  } else {
-    let a2 =
-      rExpr
-      ->Result.flatMap(expr =>
-        Expression.reduceExpression(expr, Belt.Map.String.empty, ExpressionValue.defaultEnvironment)
-      )
-      ->ExpressionValue.toStringResultOkless
-    (a1, a2)->expect->toEqual((answer, v))
-  }
-}
-
-let testToExpression = (expr, answer, ~v="_", ()) =>
-  test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
-
-module MySkip = {
-  let testToExpression = (expr, answer, ~v="_", ()) =>
-    Skip.test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
-}
-
-module MyOnly = {
-  let testToExpression = (expr, answer, ~v="_", ()) =>
-    Only.test(expr, () => expectToExpressionToBe(expr, answer, ~v, ()))
-}
 
 describe("Peggy to Expression", () => {
   describe("literals operators parenthesis", () => {

packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_ToExpression_type_test.res

@@ -0,0 +1,99 @@
+open Jest
+open Reducer_Peggy_TestHelpers
+
+describe("Peggy Types to Expression", () => {
+  describe("type of", () => {
+    testToExpression(
+      "p: number",
+      "{(:$_typeOf_$ :p #number)}",
+      ~v="{_typeReferences_: {p: #number}}",
+      (),
+    )
+  })
+  describe("type alias", () => {
+    testToExpression(
+      "type index=number",
+      "{(:$_typeAlias_$ #index #number)}",
+      ~v="{_typeAliases_: {index: #number}}",
+      (),
+    )
+  })
+  describe("type or", () => {
+    testToExpression(
+      "answer: number|string|distribution",
+      "{(:$_typeOf_$ :answer (:$_typeOr_$ (:$_constructArray_$ (#number #string #distribution))))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeOr',typeOr: [#number,#string,#distribution]}}}",
+      (),
+    )
+  })
+  describe("type function", () => {
+    testToExpression(
+      "f: number=>number=>number",
+      "{(:$_typeOf_$ :f (:$_typeFunction_$ (:$_constructArray_$ (#number #number #number))))}",
+      ~v="{_typeReferences_: {f: {typeTag: 'typeFunction',inputs: [#number,#number],output: #number}}}",
+      (),
+    )
+    testToExpression(
+      "f: number=>number",
+      "{(:$_typeOf_$ :f (:$_typeFunction_$ (:$_constructArray_$ (#number #number))))}",
+      ~v="{_typeReferences_: {f: {typeTag: 'typeFunction',inputs: [#number],output: #number}}}",
+      (),
+    )
+  })
+  describe("high priority modifier", () => {
+    testToExpression(
+      "answer: number<-min(1)<-max(100)|string",
+      "{(:$_typeOf_$ :answer (:$_typeOr_$ (:$_constructArray_$ ((:$_typeModifier_max_$ (:$_typeModifier_min_$ #number 1) 100) #string))))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeOr',typeOr: [{typeTag: 'typeIdentifier',typeIdentifier: #number,min: 1,max: 100},#string]}}}",
+      (),
+    )
+    testToExpression(
+      "answer: number<-memberOf([1,3,5])",
+      "{(:$_typeOf_$ :answer (:$_typeModifier_memberOf_$ #number (:$_constructArray_$ (1 3 5))))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeIdentifier',typeIdentifier: #number,memberOf: [1,3,5]}}}",
+      (),
+    )
+    testToExpression(
+      "answer: number<-min(1)",
+      "{(:$_typeOf_$ :answer (:$_typeModifier_min_$ #number 1))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeIdentifier',typeIdentifier: #number,min: 1}}}",
+      (),
+    )
+    testToExpression(
+      "answer: number<-max(10)",
+      "{(:$_typeOf_$ :answer (:$_typeModifier_max_$ #number 10))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeIdentifier',typeIdentifier: #number,max: 10}}}",
+      (),
+    )
+    testToExpression(
+      "answer: number<-min(1)<-max(10)",
+      "{(:$_typeOf_$ :answer (:$_typeModifier_max_$ (:$_typeModifier_min_$ #number 1) 10))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeIdentifier',typeIdentifier: #number,min: 1,max: 10}}}",
+      (),
+    )
+    testToExpression(
+      "answer: number<-max(10)<-min(1)",
+      "{(:$_typeOf_$ :answer (:$_typeModifier_min_$ (:$_typeModifier_max_$ #number 10) 1))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeIdentifier',typeIdentifier: #number,max: 10,min: 1}}}",
+      (),
+    )
+  })
+  describe("low priority modifier", () => {
+    testToExpression(
+      "answer: number | string $ opaque",
+      "{(:$_typeOf_$ :answer (:$_typeModifier_opaque_$ (:$_typeOr_$ (:$_constructArray_$ (#number #string)))))}",
+      ~v="{_typeReferences_: {answer: {typeTag: 'typeOr',typeOr: [#number,#string],opaque: true}}}",
+      (),
+    )
+  })
+  describe("squiggle expressions in type modifiers", () => {
+    testToExpression(
+      "odds1 = [1,3,5]; odds2 = [7, 9]; type odds = number<-memberOf(odds1 + odds2)",
+      "{(:$_let_$ :odds1 {(:$_constructArray_$ (1 3 5))}); (:$_let_$ :odds2 {(:$_constructArray_$ (7 9))}); (:$_typeAlias_$ #odds (:$_typeModifier_memberOf_$ #number (:add :odds1 :odds2)))}",
+      ~v="{_typeAliases_: {odds: {typeTag: 'typeIdentifier',typeIdentifier: #number,memberOf: [1,3,5,7,9]}},odds1: [1,3,5],odds2: [7,9]}",
+      (),
+    )
+  })
+  // TODO: type bindings. Type bindings are not yet supported.
+  // TODO: type constructor
+})

packages/squiggle-lang/src/js/index.ts

@@ -185,5 +185,7 @@ function createTsExport(
       return tag("timeDuration", x.value);
     case "EvDeclaration":
       return tag("lambdaDeclaration", x.value);
+    case "EvTypeIdentifier":
+      return tag("typeIdentifier", x.value);
   }
 }

packages/squiggle-lang/src/js/rescript_interop.ts

@@ -69,6 +69,10 @@ export type rescriptExport =
   | {
       TAG: 12; // EvDeclaration
       _0: rescriptLambdaDeclaration;
+    }
+  | {
+      TAG: 13; // EvTypeIdentifier
+      _0: string;
     };
 
 type rescriptDist =
@@ -120,7 +124,8 @@ export type squiggleExpression =
   | tagged<"date", Date>
   | tagged<"timeDuration", number>
   | tagged<"lambdaDeclaration", lambdaDeclaration>
-  | tagged<"record", { [key: string]: squiggleExpression }>;
+  | tagged<"record", { [key: string]: squiggleExpression }>
+  | tagged<"typeIdentifier", string>;
 
 export { lambdaValue };
 
@@ -170,6 +175,8 @@ export function convertRawToTypescript(
         fn: result._0.fn,
         args: result._0.args.map(convertDeclaration),
       });
+    case 13: // EvSymbol
+      return tag("typeIdentifier", result._0);
   }
 }
 

packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn.res

@@ -52,6 +52,16 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
     | None => RERecordPropertyNotFound("Record property not found", sIndex)->Error
     }
 
+  let doAddArray = (originalA, b) => {
+    let a = originalA->Js.Array2.copy
+    let _ = Js.Array2.pushMany(a, b)
+    a->EvArray->Ok
+  }
+  let doAddString = (a, b) => {
+    let answer = Js.String2.concat(a, b)
+    answer->EvString->Ok
+  }
+
   let inspect = (value: expressionValue) => {
     Js.log(value->toString)
     value->Ok
@@ -74,6 +84,40 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
     ->Ok
   }
 
+  let doSetBindingsInNamespace = (
+    externalBindings: externalBindings,
+    symbol: string,
+    value: expressionValue,
+    namespace: string,
+  ) => {
+    let bindings = Bindings.fromExternalBindings(externalBindings)
+    let evAliases = bindings->Belt.Map.String.getWithDefault(namespace, EvRecord(Js.Dict.empty()))
+    let newEvAliases = switch evAliases {
+    | EvRecord(dict) => {
+        Js.Dict.set(dict, symbol, value)
+        dict->EvRecord
+      }
+    | _ => Js.Dict.empty()->EvRecord
+    }
+    bindings
+    ->Belt.Map.String.set(namespace, newEvAliases)
+    ->Bindings.toExternalBindings
+    ->EvRecord
+    ->Ok
+  }
+
+  let doSetTypeAliasBindings = (
+    externalBindings: externalBindings,
+    symbol: string,
+    value: expressionValue,
+  ) => doSetBindingsInNamespace(externalBindings, symbol, value, Bindings.typeAliasesKey)
+
+  let doSetTypeOfBindings = (
+    externalBindings: externalBindings,
+    symbol: string,
+    value: expressionValue,
+  ) => doSetBindingsInNamespace(externalBindings, symbol, value, Bindings.typeReferencesKey)
+
   let doExportBindings = (externalBindings: externalBindings) => EvRecord(externalBindings)->Ok
 
   let doKeepArray = (aValueArray, aLambdaValue) => {
@@ -147,6 +191,69 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
     )
   }
 
+  let typeModifier_memberOf = (aType, anArray) => {
+    let newRecord = Js.Dict.fromArray([
+      ("typeTag", EvString("typeIdentifier")),
+      ("typeIdentifier", aType),
+    ])
+    newRecord->Js.Dict.set("memberOf", anArray)
+    newRecord->EvRecord->Ok
+  }
+  let typeModifier_memberOf_update = (aRecord, anArray) => {
+    let newRecord = aRecord->Js.Dict.entries->Js.Dict.fromArray
+    newRecord->Js.Dict.set("memberOf", anArray)
+    newRecord->EvRecord->Ok
+  }
+
+  let typeModifier_min = (aType, value) => {
+    let newRecord = Js.Dict.fromArray([
+      ("typeTag", EvString("typeIdentifier")),
+      ("typeIdentifier", aType),
+    ])
+    newRecord->Js.Dict.set("min", value)
+    newRecord->EvRecord->Ok
+  }
+  let typeModifier_min_update = (aRecord, value) => {
+    let newRecord = aRecord->Js.Dict.entries->Js.Dict.fromArray
+    newRecord->Js.Dict.set("min", value)
+    newRecord->EvRecord->Ok
+  }
+
+  let typeModifier_max = (aType, value) => {
+    let newRecord = Js.Dict.fromArray([
+      ("typeTag", EvString("typeIdentifier")),
+      ("typeIdentifier", aType),
+    ])
+    newRecord->Js.Dict.set("max", value)
+    newRecord->EvRecord->Ok
+  }
+  let typeModifier_max_update = (aRecord, value) => {
+    let newRecord = aRecord->Js.Dict.entries->Js.Dict.fromArray
+    newRecord->Js.Dict.set("max", value)
+    newRecord->EvRecord->Ok
+  }
+
+  let typeModifier_opaque_update = aRecord => {
+    let newRecord = aRecord->Js.Dict.entries->Js.Dict.fromArray
+    newRecord->Js.Dict.set("opaque", EvBool(true))
+    newRecord->EvRecord->Ok
+  }
+
+  let typeOr = evArray => {
+    let newRecord = Js.Dict.fromArray([("typeTag", EvString("typeOr")), ("typeOr", evArray)])
+    newRecord->EvRecord->Ok
+  }
+  let typeFunction = anArray => {
+    let output = Belt.Array.getUnsafe(anArray, Js.Array2.length(anArray) - 1)
+    let inputs = Js.Array2.slice(anArray, ~start=0, ~end_=-1)
+    let newRecord = Js.Dict.fromArray([
+      ("typeTag", EvString("typeFunction")),
+      ("inputs", EvArray(inputs)),
+      ("output", output),
+    ])
+    newRecord->EvRecord->Ok
+  }
+
   switch call {
   | ("$_atIndex_$", [EvArray(aValueArray), EvNumber(fIndex)]) => arrayAtIndex(aValueArray, fIndex)
   | ("$_atIndex_$", [EvRecord(dict), EvString(sIndex)]) => recordAtIndex(dict, sIndex)
@@ -155,6 +262,28 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
   | ("$_exportBindings_$", [EvRecord(externalBindings)]) => doExportBindings(externalBindings)
   | ("$_setBindings_$", [EvRecord(externalBindings), EvSymbol(symbol), value]) =>
     doSetBindings(externalBindings, symbol, value)
+  | ("$_setTypeAliasBindings_$", [EvRecord(externalBindings), EvTypeIdentifier(symbol), value]) =>
+    doSetTypeAliasBindings(externalBindings, symbol, value)
+  | ("$_setTypeOfBindings_$", [EvRecord(externalBindings), EvSymbol(symbol), value]) =>
+    doSetTypeOfBindings(externalBindings, symbol, value)
+  | ("$_typeModifier_memberOf_$", [EvTypeIdentifier(typeIdentifier), EvArray(arr)]) =>
+    typeModifier_memberOf(EvTypeIdentifier(typeIdentifier), EvArray(arr))
+  | ("$_typeModifier_memberOf_$", [EvRecord(typeRecord), EvArray(arr)]) =>
+    typeModifier_memberOf_update(typeRecord, EvArray(arr))
+  | ("$_typeModifier_min_$", [EvTypeIdentifier(typeIdentifier), value]) =>
+    typeModifier_min(EvTypeIdentifier(typeIdentifier), value)
+  | ("$_typeModifier_min_$", [EvRecord(typeRecord), value]) =>
+    typeModifier_min_update(typeRecord, value)
+  | ("$_typeModifier_max_$", [EvTypeIdentifier(typeIdentifier), value]) =>
+    typeModifier_max(EvTypeIdentifier(typeIdentifier), value)
+  | ("$_typeModifier_max_$", [EvRecord(typeRecord), value]) =>
+    typeModifier_max_update(typeRecord, value)
+  | ("$_typeModifier_opaque_$", [EvRecord(typeRecord)]) => typeModifier_opaque_update(typeRecord)
+  | ("$_typeOr_$", [EvArray(arr)]) => typeOr(EvArray(arr))
+  | ("$_typeFunction_$", [EvArray(arr)]) => typeFunction(arr)
+  | ("add", [EvArray(aValueArray), EvArray(bValueArray)]) => doAddArray(aValueArray, bValueArray)
+  | ("add", [EvString(aValueString), EvString(bValueString)]) =>
+    doAddString(aValueString, bValueString)
   | ("inspect", [value, EvString(label)]) => inspectLabel(value, label)
   | ("inspect", [value]) => inspect(value)
   | ("keep", [EvArray(aValueArray), EvLambda(aLambdaValue)]) =>

packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res

@@ -4,6 +4,7 @@
   Macros are used to define language building blocks. They are like Lisp macros.
 */
 module Bindings = Reducer_Expression_Bindings
+module ErrorValue = Reducer_ErrorValue
 module ExpressionBuilder = Reducer_Expression_ExpressionBuilder
 module ExpressionT = Reducer_Expression_T
 module ExpressionValue = ReducerInterface.ExpressionValue
@@ -12,7 +13,7 @@ module Result = Belt.Result
 open Reducer_Expression_ExpressionBuilder
 
 type environment = ExpressionValue.environment
-type errorValue = Reducer_ErrorValue.errorValue
+type errorValue = ErrorValue.errorValue
 type expression = ExpressionT.expression
 type expressionValue = ExpressionValue.expressionValue
 type expressionWithContext = ExpressionWithContext.expressionWithContext
@@ -23,84 +24,78 @@ let dispatchMacroCall = (
   environment,
   reduceExpression: ExpressionT.reducerFn,
 ): result<expressionWithContext, errorValue> => {
-  let doBindStatement = (bindingExpr: expression, statement: expression, environment) =>
+  let useExpressionToSetBindings = (bindingExpr: expression, environment, statement, newCode) => {
-    switch statement {
+    let rExternalBindingsValue = reduceExpression(bindingExpr, bindings, environment)
-    | ExpressionT.EList(list{ExpressionT.EValue(EvCall("$_let_$")), symbolExpr, statement}) => {
-        let rExternalBindingsValue = reduceExpression(bindingExpr, bindings, environment)
 
-        rExternalBindingsValue->Result.flatMap(externalBindingsValue => {
+    rExternalBindingsValue->Result.flatMap(externalBindingsValue => {
-          let newBindings = Bindings.fromValue(externalBindingsValue)
+      let newBindings = Bindings.fromValue(externalBindingsValue)
 
-          // Js.log(
+      let rNewStatement = Bindings.replaceSymbols(newBindings, statement)
-          //   `bindStatement ${Bindings.toString(newBindings)}<==${ExpressionT.toString(
+      rNewStatement->Result.map(boundStatement =>
-          //       bindingExpr,
+        ExpressionWithContext.withContext(
-          //     )} statement: $_let_$ ${ExpressionT.toString(symbolExpr)}=${ExpressionT.toString(
+          newCode(newBindings->Bindings.toExternalBindings->eRecord, boundStatement),
-          //       statement,
+          newBindings,
-          //     )}`,
+        )
-          // )
+      )
+    })
+  }
 
-          let rNewStatement = Bindings.replaceSymbols(newBindings, statement)
+  let correspondingSetBindingsFn = (fnName: string): string =>
-          rNewStatement->Result.map(newStatement =>
+    switch fnName {
-            ExpressionWithContext.withContext(
+    | "$_let_$" => "$_setBindings_$"
-              eFunction(
+    | "$_typeOf_$" => "$_setTypeOfBindings_$"
-                "$_setBindings_$",
+    | "$_typeAlias_$" => "$_setTypeAliasBindings_$"
-                list{newBindings->Bindings.toExternalBindings->eRecord, symbolExpr, newStatement},
+    | _ => ""
-              ),
-              newBindings,
-            )
-          )
-        })
-      }
-    | _ => REAssignmentExpected->Error
     }
 
+  let doBindStatement = (bindingExpr: expression, statement: expression, environment) => {
+    let defaultStatement = ErrorValue.REAssignmentExpected->Error
+    switch statement {
+    | ExpressionT.EList(list{ExpressionT.EValue(EvCall(callName)), symbolExpr, statement}) => {
+        let setBindingsFn = correspondingSetBindingsFn(callName)
+        if setBindingsFn !== "" {
+          useExpressionToSetBindings(bindingExpr, environment, statement, (
+            newBindingsExpr,
+            boundStatement,
+          ) => eFunction(setBindingsFn, list{newBindingsExpr, symbolExpr, boundStatement}))
+        } else {
+          defaultStatement
+        }
+      }
+    | _ => defaultStatement
+    }
+  }
+
   let doBindExpression = (bindingExpr: expression, statement: expression, environment): result<
     expressionWithContext,
     errorValue,
-  > =>
+  > => {
-    switch statement {
+    let defaultStatement = () =>
-    | ExpressionT.EList(list{ExpressionT.EValue(EvCall("$_let_$")), symbolExpr, statement}) => {
+      useExpressionToSetBindings(bindingExpr, environment, statement, (
-        let rExternalBindingsValue = reduceExpression(bindingExpr, bindings, environment)
+        _newBindingsExpr,
+        boundStatement,
+      ) => boundStatement)
 
-        rExternalBindingsValue->Result.flatMap(externalBindingsValue => {
+    switch statement {
-          let newBindings = Bindings.fromValue(externalBindingsValue)
+    | ExpressionT.EList(list{ExpressionT.EValue(EvCall(callName)), symbolExpr, statement}) => {
-          let rNewStatement = Bindings.replaceSymbols(newBindings, statement)
+        let setBindingsFn = correspondingSetBindingsFn(callName)
-          rNewStatement->Result.map(newStatement =>
+        if setBindingsFn !== "" {
-            ExpressionWithContext.withContext(
+          useExpressionToSetBindings(bindingExpr, environment, statement, (
-              eFunction(
+            newBindingsExpr,
-                "$_exportBindings_$",
+            boundStatement,
-                list{
+          ) =>
-                  eFunction(
+            eFunction(
-                    "$_setBindings_$",
+              "$_exportBindings_$",
-                    list{
+              list{eFunction(setBindingsFn, list{newBindingsExpr, symbolExpr, boundStatement})},
-                      newBindings->Bindings.toExternalBindings->eRecord,
-                      symbolExpr,
-                      newStatement,
-                    },
-                  ),
-                },
-              ),
-              newBindings,
             )
           )
-        })
+        } else {
-      }
+          defaultStatement()
-    | _ => {
+        }
-        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)
-          )
-        })
       }
+    | _ => defaultStatement()
     }
+  }
 
   let doBlock = (exprs: list<expression>, _bindings: ExpressionT.bindings, _environment): result<
     expressionWithContext,

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res

@@ -75,9 +75,9 @@ and reduceValueList = (valueList: list<expressionValue>, environment): result<
 > =>
   switch valueList {
   | list{EvCall(fName), ...args} => {
-      let rCheckedArgs = switch fName == "$_setBindings_$" {
+      let rCheckedArgs = switch fName {
-      | false => args->Lambda.checkIfReduced
+      | "$_setBindings_$" | "$_setTypeOfBindings_$" | "$_setTypeAliasBindings_$" => args->Ok
-      | true => args->Ok
+      | _ => args->Lambda.checkIfReduced
       }
 
       rCheckedArgs->Result.flatMap(checkedArgs =>

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Bindings.res

@@ -10,13 +10,8 @@ type externalBindings = ReducerInterface_ExpressionValue.externalBindings
 
 let defaultBindings: ExpressionT.bindings = Belt.Map.String.empty
 
-let fromExternalBindings = (externalBindings: externalBindings): ExpressionT.bindings => {
+let typeAliasesKey = "_typeAliases_"
-  let keys = Js.Dict.keys(externalBindings)
+let typeReferencesKey = "_typeReferences_"
-  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)
@@ -27,6 +22,50 @@ let toExternalBindings = (bindings: ExpressionT.bindings): externalBindings => {
   })
 }
 
+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 fromExternalBindings = (externalBindings: externalBindings): ExpressionT.bindings => {
+  // TODO: This code will be removed in the future when maps are used instead of records. Please don't mind this function for now.
+
+  let internalBindings0 = fromExternalBindings_(externalBindings)
+
+  let oExistingTypeAliases = Belt.Map.String.get(internalBindings0, typeAliasesKey)
+  let internalBindings1 = Belt.Option.mapWithDefault(
+    oExistingTypeAliases,
+    internalBindings0,
+    existingTypeAliases => {
+      let newTypeAliases = switch existingTypeAliases {
+      | EvRecord(actualTypeAliases) =>
+        actualTypeAliases->fromExternalBindings_->toExternalBindings->ExpressionValue.EvRecord
+      | _ => existingTypeAliases
+      }
+      Belt.Map.String.set(internalBindings0, typeAliasesKey, newTypeAliases)
+    },
+  )
+
+  let oExistingTypeReferences = Belt.Map.String.get(internalBindings1, typeReferencesKey)
+  let internalBindings2 = Belt.Option.mapWithDefault(
+    oExistingTypeReferences,
+    internalBindings1,
+    existingTypeReferences => {
+      let newTypeReferences = switch existingTypeReferences {
+      | EvRecord(actualTypeReferences) =>
+        actualTypeReferences->fromExternalBindings_->toExternalBindings->ExpressionValue.EvRecord
+      | _ => existingTypeReferences
+      }
+      Belt.Map.String.set(internalBindings0, typeReferencesKey, newTypeReferences)
+    },
+  )
+
+  internalBindings2
+}
+
 let fromValue = (aValue: expressionValue) =>
   switch aValue {
   | EvRecord(externalBindings) => fromExternalBindings(externalBindings)

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res

@@ -64,3 +64,6 @@ let eBindExpression = (bindingExpr: expression, expression: expression): express
 
 let eBindExpressionDefault = (expression: expression): expression =>
   eFunction("$$_bindExpression_$$", list{expression})
+
+let eTypeIdentifier = (name: string): expression =>
+  name->BExpressionValue.EvTypeIdentifier->BExpressionT.EValue

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_GeneratedParser.peggy

@@ -36,11 +36,6 @@
     '[]': '$_atIndex_$',
   }
 
-  function nodeBlock(statements) {return{type: 'Block', statements: statements}}
-  function nodeBoolean(value) {return {type: 'Boolean', value: value}}
-  function nodeCallIndentifier(value) {return {type: 'CallIdentifier', value: value}}
-  function nodeExpression(args) {return {type: 'Expression', nodes: args}}
-  function nodeFloat(value) {return {type: 'Float', value: value}}
   function makeFunctionCall(fn, args) {
     if (fn === '$$_applyAll_$$') {
       // Any list of values is applied from left to right anyway. 
@@ -52,6 +47,16 @@
       return nodeExpression([nodeCallIndentifier(fn), ...args]) 
     }
   }
+
+  function apply(fn, arg) { return makeFunctionCall(fn, [arg]); }
+  function constructArray(elems)  { return apply('$_constructArray_$', nodeExpression(elems)); }
+  function constructRecord(elems) { return apply('$_constructRecord_$', nodeExpression(elems)); }
+
+  function nodeBlock(statements) {return{type: 'Block', statements: statements}}
+  function nodeBoolean(value) {return {type: 'Boolean', value: value}}
+  function nodeCallIndentifier(value) {return {type: 'CallIdentifier', value: value}}
+  function nodeExpression(args) {return {type: 'Expression', nodes: args}}
+  function nodeFloat(value) {return {type: 'Float', value: value}}
   function nodeIdentifier(value) {return {type: 'Identifier', value: value}}
   function nodeInteger(value) {return {type: 'Integer', value: value}}
   function nodeKeyValue(key, value) { 
@@ -61,9 +66,12 @@
   function nodeLetStatment(variable, value) {return {type: 'LetStatement', variable: variable, value: value}}
   function nodeString(value) {return {type: 'String', value: value}}
   function nodeTernary(condition, trueExpression, falseExpression) {return {type: 'Ternary', condition: condition, trueExpression: trueExpression, falseExpression: falseExpression}}
+  
+  function nodeTypeIdentifier(typeValue) {return {type: 'TypeIdentifier', value: typeValue}}
 }}
 
 start
+  // = _nl start:typeExpression _nl finalComment?  {return start}
   = _nl start:outerBlock _nl finalComment?  {return start}
 
 zeroOMoreArgumentsBlockOrExpression = innerBlockOrExpression / lambda
@@ -96,6 +104,7 @@ array_statements
 statement 
   = letStatement
   / defunStatement
+  / typeStatement
 
 letStatement 
   = variable:identifier _ assignmentOp _nl value:zeroOMoreArgumentsBlockOrExpression
@@ -205,7 +214,7 @@ chainFunctionCall
 
 unary
   = unaryOperator:unaryOperator _nl right:(unary/postOperator)
-  { return makeFunctionCall(unaryToFunction[unaryOperator], [right])}
+  { return apply(unaryToFunction[unaryOperator], right)}
   / postOperator
   
   unaryOperator "unary operator"
@@ -267,7 +276,7 @@ number = number:(float / integer) unit:identifier?
     if (unit === null)
       { return number }
     else
-      { return makeFunctionCall('fromUnit_'+unit.value, [number]) 
+      { return apply('fromUnit_'+unit.value, number) 
       }
   }
 
@@ -301,9 +310,9 @@ lambda
 
 arrayConstructor 'array'
   = '[' _nl ']'
-    { return makeFunctionCall('$_constructArray_$', [nodeExpression([])])}
+    { return constructArray([]); }
   / '[' _nl args:array_elements _nl ']' 
-    { return makeFunctionCall('$_constructArray_$', [nodeExpression(args)])}
+    { return constructArray(args); }
 
   array_elements 
     = head:expression tail:(_ ',' _nl @expression)* 
@@ -311,7 +320,7 @@ arrayConstructor 'array'
 
 recordConstructor  'record'
   = '{' _nl args:array_recordArguments _nl '}' 
-  { return makeFunctionCall('$_constructRecord_$', [nodeExpression(args)])}
+  { return constructRecord(args); }
 
   array_recordArguments 
     = head:keyValuePair tail:(_ ',' _nl @keyValuePair)* 
@@ -321,6 +330,8 @@ recordConstructor  'record'
     = key:expression _ ':' _nl value:expression 
     { return nodeKeyValue(key, value)}
 
+// Separators
+
 _ 'whitespace'
   = whiteSpaceCharactersOrComment*
 
@@ -351,4 +362,79 @@ statementSeparator 'statement separator'
     newLine "newline"
       = [\n\r]
 
+// Types
 
+noArguments = ('(' _nl ')' )?
+
+typeIdentifier 'type identifier'
+  = ([a-z]+[_a-z0-9]i*) {return nodeTypeIdentifier(text())} 
+
+typeConstructorIdentifier 'type constructor identifier'
+  = ([A-Z]+[_a-z0-9]i*) {return nodeTypeIdentifier(text())} 
+
+typeExpression = typePostModifierExpression
+
+typePostModifierExpression = head:typeOr tail:(_ '$' _nl @typeModifier)*
+  { 
+    return tail.reduce((result, element) => {
+      return makeFunctionCall('$_typeModifier_'+element.modifier.value+'_$', [result, ...element.args])
+    }, head)
+  }
+
+typeOr = head:typeFunction tail:(_ '|' _nl @typeFunction)*
+  { return tail.length === 0 ? head : apply('$_typeOr_$', constructArray([head, ...tail])); }
+
+typeFunction = head:typeModifierExpression tail:(_ '=>' _nl @typeModifierExpression)*    
+  { return tail.length === 0 ? head : apply( '$_typeFunction_$', constructArray([head, ...tail])); }
+
+typeModifierExpression = head:basicType tail:(_ '<-' _nl @typeModifier)* 
+  { 
+    return tail.reduce((result, element) => {
+      return makeFunctionCall('$_typeModifier_'+element.modifier.value+'_$', [result, ...element.args])
+    }, head)
+  }
+
+  typeModifier 
+    = modifier:identifier _ '(' _nl args:array_elements _nl ')' 
+      { return {modifier: modifier, args: args}; }
+    / modifier:identifier _ noArguments
+      { return {modifier: modifier, args: []}; }
+  
+basicType = typeConstructor / typeArray / typeRecord / typeInParanthesis / typeIdentifier
+
+typeArray = '[' _nl elem:typeExpression _nl ']' 
+  {return apply('$_typeArray_$', elem)}
+
+typeRecord = '{' _nl elems:array_typeRecordArguments _nl '}' 
+  { return apply('$_typeRecord_$', constructRecord(elems)); }  
+
+  array_typeRecordArguments 
+    = head:typeKeyValuePair tail:(_ ',' _nl @typeKeyValuePair)* 
+    { return [head, ...tail]; }
+
+  typeKeyValuePair 
+    = key:identifier _ ':' _nl value:typeExpression 
+    { return nodeKeyValue(key, value)}
+
+typeConstructor 
+  = constructor:typeConstructorIdentifier _ '(' _nl args:array_types _nl ')' 
+    { return makeFunctionCall('$_typeConstructor_$', [constructor, constructArray(args)]); }
+  / constructor:typeConstructorIdentifier _ noArguments
+    { return makeFunctionCall('$_typeConstructor_$', [constructor, constructArray([])]); }
+
+  array_types = head:typeExpression tail:(_ ',' _nl @typeExpression)* 
+    { return [head, ...tail]; }
+
+typeStatement = typeAliasStatement / typeOfStatement
+typeAliasStatement = 'type' __nl typeIdentifier:typeIdentifier _nl '=' _nl typeExpression:typeExpression 
+  { return makeFunctionCall('$_typeAlias_$', [typeIdentifier, typeExpression])}
+typeOfStatement = identifier:identifier _ ':' _nl typeExpression:typeExpression
+  { return makeFunctionCall('$_typeOf_$', [identifier, typeExpression])}
+
+typeInParanthesis = '(' _nl typeExpression:typeExpression _nl ')' {return typeExpression}
+
+// TODO: min max example
+// TODO: Example of foo = {a: 2, b: 5}; type fooKeys = string $ memberOf(foo->keys)
+// TODO: Example of memberOf( [1,2,3] )
+// TODO: Example of $ 
+// TODO: Cons(a, list) | EmptyList

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res

@@ -24,6 +24,7 @@ type nodeLambda = {...node, "args": array<nodeIdentifier>, "body": nodeBlock}
 type nodeLetStatement = {...node, "variable": nodeIdentifier, "value": node}
 type nodeString = {...node, "value": string}
 type nodeTernary = {...node, "condition": node, "trueExpression": node, "falseExpression": node}
+type nodeTypeIdentifier = {...node, "value": string}
 
 type peggyNode =
   | PgNodeBlock(nodeBlock)
@@ -38,6 +39,7 @@ type peggyNode =
   | PgNodeLetStatement(nodeLetStatement)
   | PgNodeString(nodeString)
   | PgNodeTernary(nodeTernary)
+  | PgNodeTypeIdentifier(nodeTypeIdentifier)
 
 external castNodeBlock: node => nodeBlock = "%identity"
 external castNodeBoolean: node => nodeBoolean = "%identity"
@@ -51,6 +53,7 @@ external castNodeLambda: node => nodeLambda = "%identity"
 external castNodeLetStatement: node => nodeLetStatement = "%identity"
 external castNodeString: node => nodeString = "%identity"
 external castNodeTernary: node => nodeTernary = "%identity"
+external castNodeTypeIdentifier: node => nodeTypeIdentifier = "%identity"
 
 exception UnsupportedPeggyNodeType(string) // This should never happen; programming error
 let castNodeType = (node: node) =>
@@ -67,6 +70,7 @@ let castNodeType = (node: node) =>
   | "LetStatement" => node->castNodeLetStatement->PgNodeLetStatement
   | "String" => node->castNodeString->PgNodeString
   | "Ternary" => node->castNodeTernary->PgNodeTernary
+  | "TypeIdentifier" => node->castNodeTypeIdentifier->PgNodeTypeIdentifier
   | _ => raise(UnsupportedPeggyNodeType(node["type"]))
   }
 
@@ -98,6 +102,7 @@ let rec pgToString = (peggyNode: peggyNode): string => {
     toString(node["trueExpression"]) ++
     " " ++
     toString(node["falseExpression"]) ++ ")"
+  | PgNodeTypeIdentifier(node) => `#${node["value"]}`
   }
 }
 and toString = (node: node): string => node->castNodeType->pgToString

packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_ToExpression.res

@@ -44,5 +44,7 @@ let rec fromNode = (node: Parse.node): expression => {
         fromNode(nodeTernary["falseExpression"]),
       },
     )
+  | PgNodeTypeIdentifier(nodeTypeIdentifier) =>
+    ExpressionBuilder.eTypeIdentifier(nodeTypeIdentifier["value"])
   }
 }

packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res

@@ -23,6 +23,7 @@ type rec expressionValue =
   | EvDate(Js.Date.t)
   | EvTimeDuration(float)
   | EvDeclaration(lambdaDeclaration)
+  | EvTypeIdentifier(string)
 and record = Js.Dict.t<expressionValue>
 and externalBindings = record
 and lambdaValue = {
@@ -58,6 +59,7 @@ let rec toString = aValue =>
   | EvDate(date) => DateTime.Date.toString(date)
   | EvTimeDuration(t) => DateTime.Duration.toString(t)
   | EvDeclaration(d) => Declaration.toString(d, r => toString(EvLambda(r)))
+  | EvTypeIdentifier(id) => `#${id}`
   }
 and toStringRecord = aRecord => {
   let pairs =
@@ -83,6 +85,7 @@ let toStringWithType = aValue =>
   | EvDate(_) => `Date::${toString(aValue)}`
   | EvTimeDuration(_) => `Date::${toString(aValue)}`
   | EvDeclaration(_) => `Declaration::${toString(aValue)}`
+  | EvTypeIdentifier(_) => `TypeIdentifier::${toString(aValue)}`
   }
 
 let argsToString = (args: array<expressionValue>): string => {
@@ -129,6 +132,7 @@ type expressionValueType =
   | EvtDate
   | EvtTimeDuration
   | EvtDeclaration
+  | EvtTypeIdentifier
 
 type functionCallSignature = CallSignature(string, array<expressionValueType>)
 type functionDefinitionSignature =
@@ -149,6 +153,7 @@ let valueToValueType = value =>
   | EvDate(_) => EvtDate
   | EvTimeDuration(_) => EvtTimeDuration
   | EvDeclaration(_) => EvtDeclaration
+  | EvTypeIdentifier(_) => EvtTypeIdentifier
   }
 
 let functionCallToCallSignature = (functionCall: functionCall): functionCallSignature => {
@@ -171,6 +176,7 @@ let valueTypeToString = (valueType: expressionValueType): string =>
   | EvtDate => `Date`
   | EvtTimeDuration => `Duration`
   | EvtDeclaration => `Declaration`
+  | EvtTypeIdentifier => `TypeIdentifier`
   }
 
 let functionCallSignatureToString = (functionCallSignature: functionCallSignature): string => {