define lambdaValue record as payload

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

@@ -26,10 +26,10 @@ let eFunction = (fName: string, lispArgs: list<expression>): expression => {
 }
 
 let eLambda = (parameters: array<string>, context, expr) =>
-  BExpressionValue.EvLambda(
-    parameters,
-    context,
-    expr->castExpressionToInternalCode,
+  BExpressionValue.EvLambda({
+    parameters: parameters,
+    context: context,
+    body: expr->castExpressionToInternalCode}
   )->BExpressionT.EValue
 
 let eNumber = aNumber => aNumber->BExpressionValue.EvNumber->BExpressionT.EValue

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

@@ -30,6 +30,6 @@ let applyParametersToLambda = (
   reducer(newExpression, bindings, environment)
 }
 
-let doLambdaCall = ((parameters, context, internal), args, environment, reducer) => {
-  applyParametersToLambda(internal, parameters, args, context, environment, reducer)
+let doLambdaCall = (lambdaValue: ExpressionValue.lambdaValue, args, environment, reducer) => {
+  applyParametersToLambda(lambdaValue.body, lambdaValue.parameters, args, lambdaValue.context, environment, reducer)
 }

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

@@ -15,15 +15,19 @@ type rec expressionValue =
   | EvBool(bool)
   | EvCall(string) // External function call
   | EvDistribution(DistributionTypes.genericDist)
-  | EvLambda((array<string>, record, internalCode))
+  | EvLambda(lambdaValue)
   | EvNumber(float)
   | 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 = record
 @genType
 let defaultExternalBindings: externalBindings = Js.Dict.empty()
 
@@ -41,8 +45,8 @@ let rec toString = aValue =>
     }
   | EvBool(aBool) => Js.String.make(aBool)
   | EvCall(fName) => `:${fName}`
-  | EvLambda((parameters, _context, _internalCode)) =>
-    `lambda(${Js.Array2.toString(parameters)}=>internal)`
+  | EvLambda(lambdaValue) =>
+    `lambda(${Js.Array2.toString(lambdaValue.parameters)}=>internal code)`
   | EvNumber(aNumber) => Js.String.make(aNumber)
   | EvString(aString) => `'${aString}'`
   | EvSymbol(aString) => `:${aString}`
@@ -65,7 +69,7 @@ let toStringWithType = aValue =>
   | EvBool(_) => `Bool::${toString(aValue)}`
   | EvCall(_) => `Call::${toString(aValue)}`
   | EvDistribution(_) => `Distribution::${toString(aValue)}`
-  | EvLambda((_parameters, _context, _internalCode)) => `Lambda::${toString(aValue)}`
+  | EvLambda(_) => `Lambda::${toString(aValue)}`
   | EvNumber(_) => `Number::${toString(aValue)}`
   | EvRecord(_) => `Record::${toString(aValue)}`
   | EvString(_) => `String::${toString(aValue)}`