diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
index 6243b380..0fdb890d 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res
@@ -91,7 +91,7 @@ let rec reduceExpression = (expression: t, bindings: T.bindings): result<express
     switch valueList {
     | list{EvCall(fName), ...args} => (fName, args->Belt.List.toArray)->BuiltIn.dispatch
     // "(lambda(x=>internal) param)"
-    | list{EvLambda(parameters, internal), ...args} =>
+    | list{EvLambda((parameters, internal)), ...args} =>
       applyParametersToLambda(internal, parameters, args)
     | _ => valueList->Belt.List.toArray->ExpressionValue.EvArray->Ok
     }
@@ -121,7 +121,7 @@ let rec reduceExpression = (expression: t, bindings: T.bindings): result<express
   let rec reduceExpandedExpression = (expression: t): result<expressionValue, 'e> =>
     switch expression {
     | T.EList(list{T.EValue(EvCall("$lambda")), T.EParameters(parameters), functionDefinition}) =>
-      EvLambda(parameters, functionDefinition->castExpressionToInternalCode)->Ok
+      EvLambda((parameters, functionDefinition->castExpressionToInternalCode))->Ok
     | T.EValue(value) => value->Ok
     | T.EList(list) => {
         let racc: result<list<expressionValue>, 'e> = list->Belt.List.reduceReverse(Ok(list{}), (
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
index 1536be74..2b11a62f 100644
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
@@ -14,7 +14,7 @@ type rec expressionValue =
   | EvBool(bool)
   | EvCall(string) // External function call
   | EvDistribution(GenericDist_Types.genericDist)
-  | EvLambda(array<string>, internalCode)
+  | EvLambda((array<string>, internalCode))
   | EvNumber(float)
   | EvRecord(Js.Dict.t<expressionValue>)
   | EvString(string)
@@ -29,7 +29,7 @@ let rec toString = aValue =>
   switch aValue {
   | EvBool(aBool) => Js.String.make(aBool)
   | EvCall(fName) => `:${fName}`
-  | EvLambda(parameters, _internalCode) => `lambda(${Js.Array2.toString(parameters)}=>internal)`
+  | EvLambda((parameters, _internalCode)) => `lambda(${Js.Array2.toString(parameters)}=>internal)`
   | EvNumber(aNumber) => Js.String.make(aNumber)
   | EvString(aString) => `'${aString}'`
   | EvSymbol(aString) => `:${aString}`
@@ -60,7 +60,7 @@ let toStringWithType = aValue =>
   | EvBool(_) => `Bool::${toString(aValue)}`
   | EvCall(_) => `Call::${toString(aValue)}`
   | EvDistribution(_) => `Distribution::${toString(aValue)}`
-  | EvLambda(_parameters, _internalCode) => `Lambda::${toString(aValue)}`
+  | EvLambda((_parameters, _internalCode)) => `Lambda::${toString(aValue)}`
   | EvNumber(_) => `Number::${toString(aValue)}`
   | EvRecord(_) => `Record::${toString(aValue)}`
   | EvString(_) => `String::${toString(aValue)}`