Merge pull request #226 from umuro/reducer-dev

Reducer dev

packages/squiggle-lang/__tests__/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res

@@ -6,15 +6,18 @@ open Expect
 let expectEvalToBe = (expr: string, answer: string) =>
   Reducer.evaluate(expr)->ExpressionValue.toStringResult->expect->toBe(answer)
 
+let testEval = (expr, answer) =>
+  test(expr, () => expectEvalToBe(expr, answer))
+
 describe("builtin", () => {
   // All MathJs operators and functions are available for string, number and boolean
   // .e.g + - / * > >= < <= == /= not and or
   // See https://mathjs.org/docs/expressions/syntax.html
   // See https://mathjs.org/docs/reference/functions.html
-  test("-1", () => expectEvalToBe("-1", "Ok(-1)"))
-  test("1-1", () => expectEvalToBe("1-1", "Ok(0)"))
-  test("2>1", () => expectEvalToBe("2>1", "Ok(true)"))
-  test("concat('a','b')", () => expectEvalToBe("concat('a','b')", "Ok('ab')"))
+  testEval("-1", "Ok(-1)")
+  testEval("1-1", "Ok(0)")
+  testEval("2>1", "Ok(true)")
+  testEval("concat('a','b')", "Ok('ab')")
 })
 
 describe("builtin exception", () => {

packages/squiggle-lang/__tests__/Reducer/Reducer_MathJs/Reducer_MathJsParse_test.res

@@ -7,45 +7,60 @@ open Expect
 let expectParseToBe = (expr, answer) =>
   Parse.parse(expr)->Result.flatMap(Parse.castNodeType)->Parse.toStringResult->expect->toBe(answer)
 
+let testParse = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
+
+let testDescriptionParse = (desc, expr, answer) => test(desc, () => expectParseToBe(expr, answer))
+
+module MySkip = {
+  let testParse = (expr, answer) => Skip.test(expr, () => expectParseToBe(expr, answer))
+
+  let testDescriptionParse = (desc, expr, answer) => Skip.test(desc, () => expectParseToBe(expr, answer))
+}
+
 describe("MathJs parse", () => {
   describe("literals operators paranthesis", () => {
-    test("1", () => expectParseToBe("1", "1"))
-    test("'hello'", () => expectParseToBe("'hello'", "'hello'"))
-    test("true", () => expectParseToBe("true", "true"))
-    test("1+2", () => expectParseToBe("1+2", "add(1, 2)"))
-    test("add(1,2)", () => expectParseToBe("add(1,2)", "add(1, 2)"))
-    test("(1)", () => expectParseToBe("(1)", "(1)"))
-    test("(1+2)", () => expectParseToBe("(1+2)", "(add(1, 2))"))
+    testParse("1", "1")
+    testParse("'hello'", "'hello'")
+    testParse("true", "true")
+    testParse("1+2", "add(1, 2)")
+    testParse("add(1,2)", "add(1, 2)")
+    testParse("(1)", "(1)")
+    testParse("(1+2)", "(add(1, 2))")
+  })
+
+  describe("multi-line", () => {
+    testParse("1; 2", "{1; 2}")
   })
 
   describe("variables", () => {
-    Skip.test("define", () => expectParseToBe("x = 1", "???"))
-    Skip.test("use", () => expectParseToBe("x", "???"))
+    testParse("x = 1", "x = 1")
+    testParse("x", "x")
+    testParse("x = 1; x", "{x = 1; x}")
   })
 
   describe("functions", () => {
-    Skip.test("define", () => expectParseToBe("identity(x) = x", "???"))
-    Skip.test("use", () => expectParseToBe("identity(x)", "???"))
+    MySkip.testParse("identity(x) = x", "???")
+    MySkip.testParse("identity(x)", "???")
   })
 
   describe("arrays", () => {
-    test("empty", () => expectParseToBe("[]", "[]"))
-    test("define", () => expectParseToBe("[0, 1, 2]", "[0, 1, 2]"))
-    test("define with strings", () => expectParseToBe("['hello', 'world']", "['hello', 'world']"))
-    Skip.test("range", () => expectParseToBe("range(0, 4)", "range(0, 4)"))
-    test("index", () => expectParseToBe("([0,1,2])[1]", "([0, 1, 2])[1]"))
+    testDescriptionParse("empty", "[]", "[]")
+    testDescriptionParse("define", "[0, 1, 2]", "[0, 1, 2]")
+    testDescriptionParse("define with strings", "['hello', 'world']", "['hello', 'world']")
+    MySkip.testParse("range(0, 4)", "range(0, 4)")
+    testDescriptionParse("index", "([0,1,2])[1]", "([0, 1, 2])[1]")
   })
 
   describe("records", () => {
-    test("define", () => expectParseToBe("{a: 1, b: 2}", "{a: 1, b: 2}"))
-    test("use", () => expectParseToBe("record.property", "record['property']"))
+    testDescriptionParse("define", "{a: 1, b: 2}", "{a: 1, b: 2}")
+    testDescriptionParse("use", "record.property", "record['property']")
   })
 
   describe("comments", () => {
-    Skip.test("define", () => expectParseToBe("# This is a comment", "???"))
+    MySkip.testDescriptionParse("define", "# This is a comment", "???")
   })
 
-  describe("if statement", () => {
-    Skip.test("define", () => expectParseToBe("if (true) { 1 } else { 0 }", "???"))
+  describe("if statement", () => { // TODO Tertiary operator instead
+    MySkip.testDescriptionParse("define", "if (true) { 1 } else { 0 }", "???")
   })
 })

packages/squiggle-lang/__tests__/Reducer/Reducer_test.res

@@ -1,6 +1,14 @@
 open Jest
 open Reducer_TestHelpers
 
+let testParseToBe = (expr, answer) => test(expr, () => expectParseToBe(expr, answer))
+
+let testDescriptionParseToBe = (desc, expr, answer) => test(desc, () => expectParseToBe(expr, answer))
+
+let testEvalToBe = (expr, answer) => test(expr, () => expectEvalToBe(expr, answer))
+
+let testDescriptionEvalToBe = (desc, expr, answer) => test(desc, () => expectEvalToBe(expr, answer))
+
 describe("reducer using mathjs parse", () => {
   // Test the MathJs parser compatibility
   // Those tests toString that there is a semantic mapping from MathJs to Expression
@@ -10,33 +18,39 @@ describe("reducer using mathjs parse", () => {
   // Those tests toString that we are converting mathjs parse tree to what we need
 
   describe("expressions", () => {
-    test("1", () => expectParseToBe("1", "Ok(1)"))
-    test("(1)", () => expectParseToBe("(1)", "Ok(1)"))
-    test("1+2", () => expectParseToBe("1+2", "Ok((:add 1 2))"))
-    test("(1+2)", () => expectParseToBe("1+2", "Ok((:add 1 2))"))
-    test("add(1,2)", () => expectParseToBe("1+2", "Ok((:add 1 2))"))
-    test("1+2*3", () => expectParseToBe("1+2*3", "Ok((:add 1 (:multiply 2 3)))"))
+    testParseToBe("1", "Ok(1)")
+    testParseToBe("(1)", "Ok(1)")
+    testParseToBe("1+2", "Ok((:add 1 2))")
+    testParseToBe("1+2", "Ok((:add 1 2))")
+    testParseToBe("1+2", "Ok((:add 1 2))")
+    testParseToBe("1+2*3", "Ok((:add 1 (:multiply 2 3)))")
   })
   describe("arrays", () => {
     //Note. () is a empty list in Lisp
     //  The only builtin structure in Lisp is list. There are no arrays
     //  [1,2,3] becomes (1 2 3)
-    test("empty", () => expectParseToBe("[]", "Ok(())"))
-    test("[1, 2, 3]", () => expectParseToBe("[1, 2, 3]", "Ok((1 2 3))"))
-    test("['hello', 'world']", () => expectParseToBe("['hello', 'world']", "Ok(('hello' 'world'))"))
-    test("index", () => expectParseToBe("([0,1,2])[1]", "Ok((:$atIndex (0 1 2) (1)))"))
+    testDescriptionParseToBe("empty", "[]", "Ok(())")
+    testParseToBe("[1, 2, 3]", "Ok((1 2 3))")
+    testParseToBe("['hello', 'world']", "Ok(('hello' 'world'))")
+    testDescriptionParseToBe("index", "([0,1,2])[1]", "Ok((:$atIndex (0 1 2) (1)))")
   })
   describe("records", () => {
-    test("define", () =>
-      expectParseToBe("{a: 1, b: 2}", "Ok((:$constructRecord (('a' 1) ('b' 2))))")
-    )
-    test("use", () =>
-      expectParseToBe(
+    testDescriptionParseToBe("define", "{a: 1, b: 2}", "Ok((:$constructRecord (('a' 1) ('b' 2))))")
+    testDescriptionParseToBe(
+      "use",
       "{a: 1, b: 2}.a",
       "Ok((:$atIndex (:$constructRecord (('a' 1) ('b' 2))) ('a')))",
     )
-    )
   })
+  describe("multi-line", () => {
+    testParseToBe("1; 2", "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) 1) 2))")
+    testParseToBe("1+1; 2+1", "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:add 1 1)) (:add 2 1)))")
+  })
+  describe("assignment", () => {
+    testParseToBe("x=1; x", "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :x 1)) :x))")
+    testParseToBe("x=1+1; x+1", "Ok((:$$bindExpression (:$$bindStatement (:$$bindings) (:$let :x (:add 1 1))) (:add :x 1)))")
+  })
+
 })
 
 describe("eval", () => {
@@ -45,37 +59,47 @@ describe("eval", () => {
   // See https://mathjs.org/docs/expressions/syntax.html
   // See https://mathjs.org/docs/reference/functions.html
   describe("expressions", () => {
-    test("1", () => expectEvalToBe("1", "Ok(1)"))
-    test("1+2", () => expectEvalToBe("1+2", "Ok(3)"))
-    test("(1+2)*3", () => expectEvalToBe("(1+2)*3", "Ok(9)"))
-    test("2>1", () => expectEvalToBe("2>1", "Ok(true)"))
-    test("concat('a ', 'b')", () => expectEvalToBe("concat('a ', 'b')", "Ok('a b')"))
-    test("log(10)", () => expectEvalToBe("log(10)", "Ok(2.302585092994046)"))
-    test("cos(10)", () => expectEvalToBe("cos(10)", "Ok(-0.8390715290764524)"))
+    testEvalToBe("1", "Ok(1)")
+    testEvalToBe("1+2", "Ok(3)")
+    testEvalToBe("(1+2)*3", "Ok(9)")
+    testEvalToBe("2>1", "Ok(true)")
+    testEvalToBe("concat('a ', 'b')", "Ok('a b')")
+    testEvalToBe("log(10)", "Ok(2.302585092994046)")
+    testEvalToBe("cos(10)", "Ok(-0.8390715290764524)")
     // TODO more built ins
   })
   describe("arrays", () => {
     test("empty array", () => expectEvalToBe("[]", "Ok([])"))
-    test("[1, 2, 3]", () => expectEvalToBe("[1, 2, 3]", "Ok([1, 2, 3])"))
-    test("['hello', 'world']", () => expectEvalToBe("['hello', 'world']", "Ok(['hello', 'world'])"))
-    test("index", () => expectEvalToBe("([0,1,2])[1]", "Ok(1)"))
-    test("index not found", () =>
-      expectEvalToBe("([0,1,2])[10]", "Error(Array index not found: 10)")
-    )
+    testEvalToBe("[1, 2, 3]", "Ok([1, 2, 3])")
+    testEvalToBe("['hello', 'world']", "Ok(['hello', 'world'])")
+    testEvalToBe("([0,1,2])[1]", "Ok(1)")
+    testDescriptionEvalToBe("index not found", "([0,1,2])[10]", "Error(Array index not found: 10)")
   })
   describe("records", () => {
     test("define", () => expectEvalToBe("{a: 1, b: 2}", "Ok({a: 1, b: 2})"))
     test("index", () => expectEvalToBe("{a: 1}.a", "Ok(1)"))
     test("index not found", () => expectEvalToBe("{a: 1}.b", "Error(Record property not found: b)"))
   })
+
+  describe("multi-line", () => {
+    testEvalToBe("1; 2", "Error(Assignment expected)")
+    testEvalToBe("1+1; 2+1", "Error(Assignment expected)")
+  })
+  describe("assignment", () => {
+    testEvalToBe("x=1; x", "Ok(1)")
+    testEvalToBe("x=1+1; x+1", "Ok(3)")
+    testEvalToBe("x=1; y=x+1; y+1", "Ok(3)")
+    testEvalToBe("1; x=1", "Error(Assignment expected)")
+    testEvalToBe("1; 1", "Error(Assignment expected)")
+    testEvalToBe("x=1; x=1", "Error(Expression expected)")
+  })
 })
 
 describe("test exceptions", () => {
-  test("javascript exception", () =>
-    expectEvalToBe("jsraise('div by 0')", "Error(JS Exception: Error: 'div by 0')")
-  )
-
-  test("rescript exception", () =>
-    expectEvalToBe("resraise()", "Error(TODO: unhandled rescript exception)")
+  testDescriptionEvalToBe(
+    "javascript exception",
+    "javascriptraise('div by 0')",
+    "Error(JS Exception: Error: 'div by 0')",
   )
+  testDescriptionEvalToBe("rescript exception", "rescriptraise()", "Error(TODO: unhandled rescript exception)")
 })

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

@@ -88,6 +88,7 @@ function tag<a, b>(x: a, y: b): tagged<a, b> {
 export type squiggleExpression =
   | tagged<"symbol", string>
   | tagged<"string", string>
+  | tagged<"call", string>
   | tagged<"array", squiggleExpression[]>
   | tagged<"boolean", boolean>
   | tagged<"distribution", Distribution>
@@ -117,6 +118,8 @@ function createTsExport(
       );
     case "EvBool":
       return tag("boolean", x.value);
+    case "EvCall":
+      return tag("call", x.value);
     case "EvDistribution":
       return tag("distribution", new Distribution(x.value, sampEnv));
     case "EvNumber":

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

@@ -14,8 +14,8 @@ exception TestRescriptException
 let callInternal = (call: functionCall): result<'b, errorValue> => {
   let callMathJs = (call: functionCall): result<'b, errorValue> =>
     switch call {
-    | ("jsraise", [msg]) => Js.Exn.raiseError(toString(msg)) // For Tests
-    | ("resraise", _) => raise(TestRescriptException) // For Tests
+    | ("javascriptraise", [msg]) => Js.Exn.raiseError(toString(msg)) // For Tests
+    | ("rescriptraise", _) => raise(TestRescriptException) // For Tests
     | call => call->toStringFunctionCall->MathJs.Eval.eval
     }
 
@@ -58,7 +58,7 @@ let callInternal = (call: functionCall): result<'b, errorValue> => {
 }
 
 /*
-  Lisp engine uses Result monad while reducing expressions
+  Reducer uses Result monad while reducing expressions
 */
 let dispatch = (call: functionCall): result<expressionValue, errorValue> =>
   try {

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

@@ -1,9 +1,14 @@
 @genType
 type errorValue =
   | REArrayIndexNotFound(string, int)
+  | REAssignmentExpected
+  | REExpressionExpected
   | REFunctionExpected(string)
   | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
+  | REMacroNotFound(string)
   | RERecordPropertyNotFound(string, string)
+  | RESymbolNotFound(string)
+  | RESyntaxError(string)
   | RETodo(string) // To do
 
 type t = errorValue
@@ -12,6 +17,8 @@ type t = errorValue
 let errorToString = err =>
   switch err {
   | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
+  | REAssignmentExpected => "Assignment expected"
+  | REExpressionExpected => "Expression expected"
   | REFunctionExpected(msg) => `Function expected: ${msg}`
   | REJavaScriptExn(omsg, oname) => {
       let answer = "JS Exception:"
@@ -25,6 +32,9 @@ let errorToString = err =>
       }
       answer
     }
+  | REMacroNotFound(macro) => `Macro not found: ${macro}`
   | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
+  | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
+  | RESyntaxError(desc) => `Syntax Error: ${desc}`
   | RETodo(msg) => `TODO: ${msg}`
   }

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

@@ -11,10 +11,11 @@ type expressionValue = ExpressionValue.expressionValue
 type t = expression
 
 /*
-  Shows the Lisp Code as text lisp code
+  Shows the expression as text of expression
 */
 let rec toString = expression =>
   switch expression {
+  | T.EBindings(bindings) => "$$bound"
   | T.EList(aList) =>
     `(${Belt.List.map(aList, aValue => toString(aValue))
       ->Extra.List.interperse(" ")
@@ -30,7 +31,7 @@ let toStringResult = codeResult =>
   }
 
 /*
-  Converts a MathJs code to Lisp Code
+  Converts a MathJs code to expression
 */
 let parse_ = (expr: string, parser, converter): result<t, errorValue> =>
   expr->parser->Result.flatMap(node => converter(node))
@@ -38,24 +39,105 @@ let parse_ = (expr: string, parser, converter): result<t, errorValue> =>
 let parse = (mathJsCode: string): result<t, errorValue> =>
   mathJsCode->parse_(MathJs.Parse.parse, MathJs.ToExpression.fromNode)
 
-module MapString = Belt.Map.String
-type bindings = MapString.t<unit>
-let defaultBindings: bindings = MapString.fromArray([])
-// TODO Define bindings for function execution context
+let defaultBindings: T.bindings = Belt.Map.String.empty
 
 /*
-  After reducing each level of code tree, we have a value list to evaluate
+  Recursively evaluate/reduce the expression (Lisp AST)
 */
-let reduceValueList = (valueList: list<expressionValue>): result<expressionValue, 'e> =>
+let rec reduceExpression = (expression: t, bindings: T.bindings): result<expressionValue, 'e> => {
+  /*
+    After reducing each level of expression(Lisp AST), we have a value list to evaluate
+ */
+  let reduceValueList = (valueList: list<expressionValue>): result<expressionValue, 'e> =>
     switch valueList {
-  | list{EvSymbol(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch
+    | list{EvCall(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch
     | _ => valueList->Belt.List.toArray->ExpressionValue.EvArray->Ok
     }
 
-/*
-  Recursively evaluate/reduce the code tree
-*/
-let rec reduceExpression = (expression: 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> => {
+    let dispatchMacroCall = (list: list<t>, bindings: T.bindings): result<t, 'e> => {
+      let rec replaceSymbols = (expression: t, bindings: T.bindings): result<t, errorValue> =>
+        switch expression {
+        | T.EValue(EvSymbol(aSymbol)) =>
+          switch bindings->Belt.Map.String.get(aSymbol) {
+          | Some(boundExpression) => boundExpression->Ok
+          | None => RESymbolNotFound(aSymbol)->Error
+          }
+        | T.EValue(_) => expression->Ok
+        | T.EBindings(_) => expression->Ok
+        | T.EList(list) => {
+            let racc = list->Belt.List.reduceReverse(Ok(list{}), (racc, each: expression) =>
+              racc->Result.flatMap(acc => {
+                each
+                ->replaceSymbols(bindings)
+                ->Result.flatMap(newNode => {
+                  acc->Belt.List.add(newNode)->Ok
+                })
+              })
+            )
+            racc->Result.map(acc => acc->T.EList)
+          }
+        }
+
+      let doBindStatement = (statement: t, bindings: T.bindings) => {
+        switch statement {
+        | T.EList(list{T.EValue(EvCall("$let")), T.EValue(EvSymbol(aSymbol)), expression}) => {
+            let rNewExpression = replaceSymbols(expression, bindings)
+            rNewExpression->Result.map(newExpression =>
+              Belt.Map.String.set(bindings, aSymbol, newExpression)->T.EBindings
+            )
+          }
+        | _ => REAssignmentExpected->Error
+        }
+      }
+
+      let doBindExpression = (expression: t, bindings: T.bindings) => {
+        switch expression {
+        | T.EList(list{T.EValue(EvCall("$let")), ..._}) => REExpressionExpected->Error
+        | _ => replaceSymbols(expression, bindings)
+        }
+      }
+
+      switch list {
+      | list{T.EValue(EvCall("$$bindings"))} => bindings->EBindings->Ok
+
+      | list{T.EValue(EvCall("$$bindStatement")), T.EBindings(bindings), statement} =>
+        doBindStatement(statement, bindings)
+      | list{T.EValue(EvCall("$$bindExpression")), T.EBindings(bindings), expression} =>
+        doBindExpression(expression, bindings)
+      | _ => list->T.EList->Ok
+      }
+    }
+
+    list->dispatchMacroCall(bindings)
+  }
+
+  let rec seekMacros = (expression: t, bindings: T.bindings): result<t, 'e> =>
+    switch expression {
+    | T.EValue(value) => expression->Ok
+    | T.EList(list) => {
+        let racc: result<list<t>, 'e> = list->Belt.List.reduceReverse(Ok(list{}), (
+          racc,
+          each: expression,
+        ) =>
+          racc->Result.flatMap(acc => {
+            each
+            ->seekMacros(bindings)
+            ->Result.flatMap(newNode => {
+              acc->Belt.List.add(newNode)->Ok
+            })
+          })
+        )
+        racc->Result.flatMap(acc => acc->doMacroCall(bindings))
+      }
+    }
+
+  let rec reduceExpandedExpression = (expression: t): result<expressionValue, 'e> =>
     switch expression {
     | T.EValue(value) => value->Ok
     | T.EList(list) => {
@@ -65,7 +147,7 @@ let rec reduceExpression = (expression: t, bindings): result<expressionValue, 'e
         ) =>
           racc->Result.flatMap(acc => {
             each
-          ->reduceExpression(bindings)
+            ->reduceExpandedExpression
             ->Result.flatMap(newNode => {
               acc->Belt.List.add(newNode)->Ok
             })
@@ -75,17 +157,23 @@ let rec reduceExpression = (expression: t, bindings): result<expressionValue, 'e
       }
     }
 
+  let rExpandedExpression: result<t, 'e> = expression->seekMacros(bindings)
+  rExpandedExpression->Result.flatMap(expandedExpression =>
+    expandedExpression->reduceExpandedExpression
+  )
+}
+
 let evalWBindingsExpression = (aExpression, bindings): result<expressionValue, 'e> =>
   reduceExpression(aExpression, bindings)
 
 /*
-  Evaluates MathJs code via Lisp using bindings and answers the result
+  Evaluates MathJs code via Reducer using bindings and answers the result
 */
-let evalWBindings = (codeText: string, bindings: bindings) => {
+let evalWBindings = (codeText: string, bindings: T.bindings) => {
   parse(codeText)->Result.flatMap(code => code->evalWBindingsExpression(bindings))
 }
 
 /*
-  Evaluates MathJs code via Lisp and answers the result
+  Evaluates MathJs code via Reducer and answers the result
 */
 let eval = (code: string) => evalWBindings(code, defaultBindings)

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

@@ -1,29 +0,0 @@
-module Result = Belt.Result
-module T = Reducer_Expression_T
-type expression = T.expression
-@genType
-type expressionValue = ReducerInterface_ExpressionValue.expressionValue
-type t = expression
-let toString: T.expression => Js.String.t
-let toStringResult: result<T.expression, 'a> => string
-let parse: string => result<expression, Reducer_ErrorValue.t>
-module MapString = Belt.Map.String
-type bindings = MapString.t<unit>
-let defaultBindings: bindings
-let reduceValueList: list<expressionValue> => result<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let reduceExpression: (expression, 'a) => result<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let evalWBindingsExpression: (expression, 'a) => result<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let evalWBindings: (string, bindings) => Result.t<
-  expressionValue,
-  Reducer_ErrorValue.t,
->
-let eval: string => Result.t<expressionValue, Reducer_ErrorValue.t>

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

@@ -1,5 +1,15 @@
 open ReducerInterface.ExpressionValue
 
+/*
+  An expression is a Lisp AST. An expression is either a primitive value or a list of expressions.
+  In the case of a list of expressions (e1, e2, e3, ...eN), the semantic is
+     apply e1, e2 -> apply e3 -> ... -> apply eN
+  This is Lisp semantics. It holds true in both eager and lazy evaluations.
+  A Lisp AST contains only expressions/primitive values to apply to their left.
+  The act of defining the semantics of a functional language is to write it in terms of Lisp AST.
+*/
 type rec expression =
   | EList(list<expression>) // A list to map-reduce
   | EValue(expressionValue) // Irreducible built-in value. Reducer should not know the internals. External libraries are responsible
+  | EBindings(bindings) // let/def kind of statements return bindings
+and bindings = Belt.Map.String.t<expression>

packages/squiggle-lang/src/rescript/Reducer/Reducer_MathJs/Reducer_MathJs_Parse.res

@@ -7,25 +7,31 @@ open Reducer_ErrorValue
 
 type node = {"type": string, "isNode": bool, "comment": string}
 type arrayNode = {...node, "items": array<node>}
-//assignmentNode
-//blockNode
+type block = {"node": node}
+type blockNode = {...node, "blocks": array<block>}
 //conditionalNode
 type constantNode = {...node, "value": unit}
 //functionAssignmentNode
-type functionNode = {...node, "fn": string, "args": array<node>}
 type indexNode = {...node, "dimensions": array<node>}
 type objectNode = {...node, "properties": Js.Dict.t<node>}
-type accessorNode = {...node, "object": node, "index": indexNode}
-type operatorNode = {...functionNode, "op": string}
+type accessorNode = {...node, "object": node, "index": indexNode, "name": string}
 
-//parenthesisNode
 type parenthesisNode = {...node, "content": node}
 //rangeNode
 //relationalNode
 type symbolNode = {...node, "name": string}
+type functionNode = {...node, "fn": unit, "args": array<node>}
+type operatorNode = {...functionNode, "op": string}
+type assignmentNode = {...node, "object": symbolNode, "value": node}
+type assignmentNodeWAccessor = {...node, "object": accessorNode, "value": node}
+type assignmentNodeWIndex = {...assignmentNodeWAccessor, "index": Js.null<indexNode>}
 
 external castAccessorNode: node => accessorNode = "%identity"
 external castArrayNode: node => arrayNode = "%identity"
+external castAssignmentNode: node => assignmentNode = "%identity"
+external castAssignmentNodeWAccessor: node => assignmentNodeWAccessor = "%identity"
+external castAssignmentNodeWIndex: node => assignmentNodeWIndex = "%identity"
+external castBlockNode: node => blockNode = "%identity"
 external castConstantNode: node => constantNode = "%identity"
 external castFunctionNode: node => functionNode = "%identity"
 external castIndexNode: node => indexNode = "%identity"
@@ -50,6 +56,8 @@ let parse = (expr: string): result<node, errorValue> =>
 type mathJsNode =
   | MjAccessorNode(accessorNode)
   | MjArrayNode(arrayNode)
+  | MjAssignmentNode(assignmentNode)
+  | MjBlockNode(blockNode)
   | MjConstantNode(constantNode)
   | MjFunctionNode(functionNode)
   | MjIndexNode(indexNode)
@@ -58,10 +66,21 @@ type mathJsNode =
   | MjParenthesisNode(parenthesisNode)
   | MjSymbolNode(symbolNode)
 
-let castNodeType = (node: node) =>
+let castNodeType = (node: node) => {
+  let decideAssignmentNode = node => {
+    let iNode = node->castAssignmentNodeWIndex
+    if Js.null == iNode["index"] && iNode["object"]["type"] == "SymbolNode" {
+      node->castAssignmentNode->MjAssignmentNode->Ok
+    } else {
+      RESyntaxError("Assignment to index or property not supported")->Error
+    }
+  }
+
   switch node["type"] {
   | "AccessorNode" => node->castAccessorNode->MjAccessorNode->Ok
   | "ArrayNode" => node->castArrayNode->MjArrayNode->Ok
+  | "AssignmentNode" => node->decideAssignmentNode
+  | "BlockNode" => node->castBlockNode->MjBlockNode->Ok
   | "ConstantNode" => node->castConstantNode->MjConstantNode->Ok
   | "FunctionNode" => node->castFunctionNode->MjFunctionNode->Ok
   | "IndexNode" => node->castIndexNode->MjIndexNode->Ok
@@ -71,6 +90,19 @@ let castNodeType = (node: node) =>
   | "SymbolNode" => node->castSymbolNode->MjSymbolNode->Ok
   | _ => RETodo(`Argg, unhandled MathJsNode: ${node["type"]}`)->Error
   }
+}
+
+external unitAsSymbolNode: unit => symbolNode = "%identity"
+external unitAsString: unit => string = "%identity"
+
+let nameOfFunctionNode = (fNode: functionNode): string => {
+  let name = fNode["fn"]
+  if Js.typeof(name) == "string" {
+    name->unitAsString
+  } else {
+    (name->unitAsSymbolNode)["name"]
+  }
+}
 
 let rec toString = (mathJsNode: mathJsNode): string => {
   let toStringValue = (a: 'a): string =>
@@ -87,9 +119,10 @@ let rec toString = (mathJsNode: mathJsNode): string => {
     ->Js.String.concatMany("")
 
   let toStringFunctionNode = (fnode: functionNode): string =>
-    `${fnode["fn"]}(${fnode["args"]->toStringNodeArray})`
+    `${fnode->nameOfFunctionNode}(${fnode["args"]->toStringNodeArray})`
 
-  let toStringObjectEntry = ((key: string, value: node)): string => `${key}: ${value->toStringMathJsNode}`
+  let toStringObjectEntry = ((key: string, value: node)): string =>
+    `${key}: ${value->toStringMathJsNode}`
 
   let toStringObjectNode = (oNode: objectNode): string =>
     `{${oNode["properties"]
@@ -103,16 +136,28 @@ let rec toString = (mathJsNode: mathJsNode): string => {
     ->Belt.Array.map(each => toStringResult(each->castNodeType))
     ->Js.String.concatMany("")
 
+  let toStringSymbolNode = (sNode: symbolNode): string => sNode["name"]
+
+  let toStringBlocks = (blocks: array<block>): string =>
+    blocks
+    ->Belt.Array.map(each => each["node"]->castNodeType->toStringResult)
+    ->Extra.Array.interperse("; ")
+    ->Js.String.concatMany("")
+
   switch mathJsNode {
-  | MjAccessorNode(aNode) => `${aNode["object"]->toStringMathJsNode}[${aNode["index"]->toStringIndexNode}]`
+  | MjAccessorNode(aNode) =>
+    `${aNode["object"]->toStringMathJsNode}[${aNode["index"]->toStringIndexNode}]`
   | MjArrayNode(aNode) => `[${aNode["items"]->toStringNodeArray}]`
+  | MjAssignmentNode(aNode) =>
+    `${aNode["object"]->toStringSymbolNode} = ${aNode["value"]->toStringMathJsNode}`
+  | MjBlockNode(bNode) => `{${bNode["blocks"]->toStringBlocks}}`
   | MjConstantNode(cNode) => cNode["value"]->toStringValue
   | MjFunctionNode(fNode) => fNode->toStringFunctionNode
   | MjIndexNode(iNode) => iNode->toStringIndexNode
   | MjObjectNode(oNode) => oNode->toStringObjectNode
   | MjOperatorNode(opNode) => opNode->castOperatorNodeToFunctionNode->toStringFunctionNode
   | MjParenthesisNode(pNode) => `(${toStringMathJsNode(pNode["content"])})`
-  | MjSymbolNode(sNode) => sNode["name"]
+  | MjSymbolNode(sNode) => sNode->toStringSymbolNode
   }
 }
 and toStringResult = (rMathJsNode: result<mathJsNode, errorValue>): string =>

packages/squiggle-lang/src/rescript/Reducer/Reducer_MathJs/Reducer_MathJs_ToExpression.res

@@ -1,11 +1,11 @@
 module ErrorValue = Reducer_ErrorValue
 module ExpressionValue = ReducerInterface.ExpressionValue
-module ExtressionT = Reducer_Expression_T
+module ExpressionT = Reducer_Expression_T
 module JavaScript = Reducer_Js
 module Parse = Reducer_MathJs_Parse
 module Result = Belt.Result
 
-type expression = ExtressionT.expression
+type expression = ExpressionT.expression
 type expressionValue = ExpressionValue.expressionValue
 type errorValue = ErrorValue.errorValue
 
@@ -18,10 +18,19 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
         )
       )
 
-    let castFunctionNode = fNode => {
-      let fn = fNode["fn"]->ExpressionValue.EvSymbol->ExtressionT.EValue
+    let toEvCallValue = (name: string): expression =>
+      name->ExpressionValue.EvCall->ExpressionT.EValue
+    let toEvSymbolValue = (name: string): expression =>
+      name->ExpressionValue.EvSymbol->ExpressionT.EValue
+
+    let passToFunction = (fName: string, rLispArgs): result<expression, errorValue> => {
+      let fn = fName->toEvCallValue
+      rLispArgs->Result.flatMap(lispArgs => list{fn, ...lispArgs}->ExpressionT.EList->Ok)
+    }
+
+    let caseFunctionNode = fNode => {
       let lispArgs = fNode["args"]->Belt.List.fromArray->fromNodeList
-      lispArgs->Result.map(argsCode => list{fn, ...argsCode}->ExtressionT.EList)
+      passToFunction(fNode->Parse.nameOfFunctionNode, lispArgs)
     }
 
     let caseObjectNode = oNode => {
@@ -34,15 +43,16 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
             fromNode(value)->Result.map(valueExpression => {
               let entryCode =
                 list{
-                  key->ExpressionValue.EvString->ExtressionT.EValue,
+                  key->ExpressionValue.EvString->ExpressionT.EValue,
                   valueExpression,
-                }->ExtressionT.EList
+                }->ExpressionT.EList
               list{entryCode, ...acc}
             })
           )
         )
-        let lispName = "$constructRecord"->ExpressionValue.EvSymbol->ExtressionT.EValue
-        rargs->Result.map(args => list{lispName, ExtressionT.EList(args)}->ExtressionT.EList)
+        rargs->Result.flatMap(args =>
+          passToFunction("$constructRecord", list{ExpressionT.EList(args)}->Ok)
+        ) // $consturctRecord gets a single argument: List of key-value paiers
       }
 
       oNode["properties"]->Js.Dict.entries->Belt.List.fromArray->fromObjectEntries
@@ -54,33 +64,75 @@ let rec fromNode = (mathJsNode: Parse.node): result<expression, errorValue> =>
         Ok(list{}),
         (racc, currentPropertyMathJsNode) =>
           racc->Result.flatMap(acc =>
-            fromNode(currentPropertyMathJsNode)->Result.map(propertyCode => list{propertyCode, ...acc})
+            fromNode(currentPropertyMathJsNode)->Result.map(propertyCode => list{
+              propertyCode,
+              ...acc,
+            })
           ),
       )
-      rpropertyCodeList->Result.map(propertyCodeList => ExtressionT.EList(propertyCodeList))
+      rpropertyCodeList->Result.map(propertyCodeList => ExpressionT.EList(propertyCodeList))
     }
 
     let caseAccessorNode = (objectNode, indexNode) => {
-      let fn = "$atIndex"->ExpressionValue.EvSymbol->ExtressionT.EValue
-
       caseIndexNode(indexNode)->Result.flatMap(indexCode => {
-        fromNode(objectNode)->Result.map(objectCode =>
-          list{fn, objectCode, indexCode}->ExtressionT.EList
+        fromNode(objectNode)->Result.flatMap(objectCode =>
+          passToFunction("$atIndex", list{objectCode, indexCode}->Ok)
         )
       })
     }
 
-    switch typedMathJsNode {
-    | MjArrayNode(aNode) =>
-      aNode["items"]->Belt.List.fromArray->fromNodeList->Result.map(list => ExtressionT.EList(list))
-    | MjConstantNode(cNode) =>
-      cNode["value"]->JavaScript.Gate.jsToEv->Result.map(v => v->ExtressionT.EValue)
-    | MjFunctionNode(fNode) => fNode->castFunctionNode
-    | MjOperatorNode(opNode) => opNode->Parse.castOperatorNodeToFunctionNode->castFunctionNode
-    | MjParenthesisNode(pNode) => pNode["content"]->fromNode
-    | MjAccessorNode(aNode) => caseAccessorNode(aNode["object"], aNode["index"])
-    | MjObjectNode(oNode) => caseObjectNode(oNode)
-    | MjSymbolNode(sNode) => sNode["name"]->ExpressionValue.EvSymbol->ExtressionT.EValue->Ok
-    | MjIndexNode(iNode) => caseIndexNode(iNode)
-    }
+    let caseAssignmentNode = aNode => {
+      let symbol = aNode["object"]["name"]->toEvSymbolValue
+      let rValueExpression = fromNode(aNode["value"])
+      rValueExpression->Result.flatMap(valueExpression => {
+        let lispArgs = list{symbol, valueExpression}->Ok
+        passToFunction("$let", lispArgs)
+      })
+    }
+
+    let caseArrayNode = aNode => {
+      aNode["items"]->Belt.List.fromArray->fromNodeList->Result.map(list => ExpressionT.EList(list))
+    }
+
+    let caseBlockNode = (bNode): result<expression, errorValue> => {
+      let blocks = bNode["blocks"]
+      let initialBindings = passToFunction("$$bindings", list{}->Ok)
+      let lastIndex = Belt.Array.length(blocks) - 1
+      blocks->Belt.Array.reduceWithIndex(initialBindings, (rPreviousBindings, block, i) => {
+        rPreviousBindings->Result.flatMap(previousBindings => {
+          let node = block["node"]
+          let rStatement: result<expression, errorValue> = node->fromNode
+          let bindName = if i == lastIndex {
+            "$$bindExpression"
+          } else {
+            "$$bindStatement"
+          }
+          rStatement->Result.flatMap((statement: expression) => {
+            let lispArgs = list{previousBindings, statement}->Ok
+            passToFunction(bindName, lispArgs)
+          })
+        })
+      })
+    }
+
+    let rFinalExpression: result<expression, errorValue> = switch typedMathJsNode {
+    | MjAccessorNode(aNode) => caseAccessorNode(aNode["object"], aNode["index"])
+    | MjArrayNode(aNode) => caseArrayNode(aNode)
+    | MjAssignmentNode(aNode) => caseAssignmentNode(aNode)
+    | MjSymbolNode(sNode) => {
+        let expr: expression = toEvSymbolValue(sNode["name"])
+        let rExpr: result<expression, errorValue> = expr->Ok
+        rExpr
+      }
+    | MjBlockNode(bNode) => caseBlockNode(bNode)
+    // | MjBlockNode(bNode) => "statement"->toEvSymbolValue->Ok
+    | MjConstantNode(cNode) =>
+      cNode["value"]->JavaScript.Gate.jsToEv->Result.flatMap(v => v->ExpressionT.EValue->Ok)
+    | MjFunctionNode(fNode) => fNode->caseFunctionNode
+    | MjIndexNode(iNode) => caseIndexNode(iNode)
+    | MjObjectNode(oNode) => caseObjectNode(oNode)
+    | MjOperatorNode(opNode) => opNode->Parse.castOperatorNodeToFunctionNode->caseFunctionNode
+    | MjParenthesisNode(pNode) => pNode["content"]->fromNode
+    }
+    rFinalExpression
   })

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

@@ -7,25 +7,30 @@ module ErrorValue = Reducer_ErrorValue
 
 @genType
 type rec expressionValue =
+  | EvArray(array<expressionValue>)
   | EvBool(bool)
+  | EvCall(string) // External function call
+  | EvDistribution(GenericDist_Types.genericDist)
   | EvNumber(float)
+  | EvRecord(Js.Dict.t<expressionValue>)
   | EvString(string)
   | EvSymbol(string)
-  | EvArray(array<expressionValue>)
-  | EvRecord(Js.Dict.t<expressionValue>)
-  | EvDistribution(GenericDist_Types.genericDist)
 
 type functionCall = (string, array<expressionValue>)
 
 let rec toString = aValue =>
   switch aValue {
   | EvBool(aBool) => Js.String.make(aBool)
+  | EvCall(fName) => `:${fName}`
   | EvNumber(aNumber) => Js.String.make(aNumber)
   | EvString(aString) => `'${aString}'`
   | EvSymbol(aString) => `:${aString}`
   | EvArray(anArray) => {
       let args =
-        anArray->Belt.Array.map(each => toString(each))->Extra_Array.interperse(", ")->Js.String.concatMany("")
+        anArray
+        ->Belt.Array.map(each => toString(each))
+        ->Extra_Array.interperse(", ")
+        ->Js.String.concatMany("")
       `[${args}]`
     }
   | EvRecord(aRecord) => {
@@ -37,12 +42,13 @@ let rec toString = aValue =>
         ->Js.String.concatMany("")
       `{${pairs}}`
     }
-  | EvDistribution(dist) => `${GenericDist.toString(dist)}`
+  | EvDistribution(dist) => GenericDist.toString(dist)
   }
 
 let toStringWithType = aValue =>
   switch aValue {
   | EvBool(_) => `Bool::${toString(aValue)}`
+  | EvCall(_) => `Call::${toString(aValue)}`
   | EvNumber(_) => `Number::${toString(aValue)}`
   | EvString(_) => `String::${toString(aValue)}`
   | EvSymbol(_) => `Symbol::${toString(aValue)}`

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

@@ -128,7 +128,8 @@ let dispatchToGenericOutput = (call: ExpressionValue.functionCall): option<
   | ("mean", [EvDistribution(dist)]) => Helpers.toFloatFn(#Mean, dist)
   | ("toString", [EvDistribution(dist)]) => Helpers.toStringFn(ToString, dist)
   | ("toSparkline", [EvDistribution(dist)]) => Helpers.toStringFn(ToSparkline(20), dist)
-  | ("toSparkline", [EvDistribution(dist), EvNumber(n)]) => Helpers.toStringFn(ToSparkline(Belt.Float.toInt(n)), dist)
+  | ("toSparkline", [EvDistribution(dist), EvNumber(n)]) =>
+    Helpers.toStringFn(ToSparkline(Belt.Float.toInt(n)), dist)
   | ("exp", [EvDistribution(a)]) =>
     // https://mathjs.org/docs/reference/functions/exp.html
     Helpers.twoDiststoDistFn(Algebraic, "pow", GenericDist.fromFloat(Math.e), a)->Some