diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res
index 535f9e56..682e1737 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn_test.res
@@ -30,8 +30,12 @@ describe("builtin exception", () => {
   )
 })
 
-Skip.describe("error reporting from collection functions", () => {
-  testEval("arr = [normal(3,2)]; map(arr, zarathsuzaWasHere)", "") 
+describe("error reporting from collection functions", () => {
+  testEval("arr=[1,2,3]; map(arr, {|x| x*2})", "Ok([2,4,6])")
+  testEval(
+    "arr = [normal(3,2)]; map(arr, zarathsuzaWasHere)",
+    "Error(zarathsuzaWasHere is not defined)",
+  )
   // FIXME: returns "Error(Function not found: map(Array,Symbol))"
   // Actually this error is correct but not informative
 })
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_functionTricks_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_functionTricks_test.res
index ba29e920..fd7485eb 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_functionTricks_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_functionTricks_test.res
@@ -25,7 +25,7 @@ describe("Arity check", () => {
   )
   testEvalToBe("f(x)=x; f(f)", "Ok(lambda(x=>internal code))")
   testEvalToBe(
-    "f(x,y)=x(y); f(z)",
+    "f(x,y)=x(y); f(1)",
     "Error(2 arguments expected. Instead 1 argument(s) were passed.)",
   )
 })
diff --git 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
index 72d599ca..141b4a37 100644
--- 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
@@ -149,8 +149,15 @@ let callInternal = (call: functionCall, environment, reducer: ExpressionT.reduce
   | ("reduceReverse", [EvArray(aValueArray), initialValue, EvLambda(aLambdaValue)]) =>
     doReduceReverseArray(aValueArray, initialValue, aLambdaValue)
   | ("reverse", [EvArray(aValueArray)]) => aValueArray->Belt.Array.reverse->EvArray->Ok
-  | (_, [EvBool(_)])  | (_, [EvNumber(_)]) | (_, [EvString(_)]) | (_, [EvBool(_), EvBool(_)])  | (_, [EvNumber(_), EvNumber(_)]) | (_, [EvString(_), EvString(_)]) => callMathJs(call)
-  | call => Error(REFunctionNotFound(call->functionCallToCallSignature->functionCallSignatureToString)) // Report full type signature as error
+  | (_, [EvBool(_)])
+  | (_, [EvNumber(_)])
+  | (_, [EvString(_)])
+  | (_, [EvBool(_), EvBool(_)])
+  | (_, [EvNumber(_), EvNumber(_)])
+  | (_, [EvString(_), EvString(_)]) =>
+    callMathJs(call)
+  | call =>
+    Error(REFunctionNotFound(call->functionCallToCallSignature->functionCallSignatureToString)) // Report full type signature as error
   }
 }
 
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 1125c193..6e3c7cab 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
@@ -76,17 +76,30 @@ and reduceValueList = (valueList: list<expressionValue>, environment): result<
   'e,
 > =>
   switch valueList {
-  | list{EvCall(fName), ...args} =>
-    (fName, args->Belt.List.toArray)->BuiltIn.dispatch(environment, reduceExpression)
+  | list{EvCall(fName), ...args} => {
+      let rCheckedArgs = switch fName == "$_setBindings_$" {
+      | false => args->Lambda.checkIfReduced
+      | true => args->Ok
+      }
 
+      rCheckedArgs->Result.flatMap(checkedArgs =>
+        (fName, checkedArgs->Belt.List.toArray)->BuiltIn.dispatch(environment, reduceExpression)
+      )
+    }
   | list{EvLambda(_)} =>
+    // TODO: remove on solving issue#558
     valueList
     ->Lambda.checkIfReduced
     ->Result.flatMap(reducedValueList =>
       reducedValueList->Belt.List.toArray->ExpressionValue.EvArray->Ok
     )
   | list{EvLambda(lamdaCall), ...args} =>
-    Lambda.doLambdaCall(lamdaCall, args, environment, reduceExpression)
+    args
+    ->Lambda.checkIfReduced
+    ->Result.flatMap(checkedArgs =>
+      Lambda.doLambdaCall(lamdaCall, checkedArgs, environment, reduceExpression)
+    )
+
   | _ =>
     valueList
     ->Lambda.checkIfReduced
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
index 958b99df..7249b135 100644
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
@@ -118,9 +118,11 @@ type expresionValueType =
   | EvtSymbol
 
 type functionCallSignature = CallSignature(string, array<expresionValueType>)
-type functionDefinitionSignature = FunctionDefinitionSignature(functionCallSignature, expresionValueType)
+type functionDefinitionSignature =
+  FunctionDefinitionSignature(functionCallSignature, expresionValueType)
 
-let valueToValueType = (value) => switch value {
+let valueToValueType = value =>
+  switch value {
   | EvArray(_) => EvtArray
   | EvArrayString(_) => EvtArray
   | EvBool(_) => EvtBool
@@ -130,11 +132,13 @@ let valueToValueType = (value) => switch value {
   | EvNumber(_) => EvtNumber
   | EvRecord(_) => EvtRecord
   | EvString(_) => EvtArray
-  | EvSymbol(_) => EvtSymbol}
+  | EvSymbol(_) => EvtSymbol
+  }
 
 let functionCallToCallSignature = (functionCall: functionCall): functionCallSignature => {
   let (fn, args) = functionCall
-  CallSignature(fn, args->Js.Array2.map(valueToValueType))}
+  CallSignature(fn, args->Js.Array2.map(valueToValueType))
+}
 
 let valueTypeToString = (valueType: expresionValueType): string =>
   switch valueType {
@@ -152,4 +156,5 @@ let valueTypeToString = (valueType: expresionValueType): string =>
 
 let functionCallSignatureToString = (functionCallSignature: functionCallSignature): string => {
   let CallSignature(fn, args) = functionCallSignature
-  `${fn}(${args->Js.Array2.map(valueTypeToString)->Js.Array2.toString})`}
\ No newline at end of file
+  `${fn}(${args->Js.Array2.map(valueTypeToString)->Js.Array2.toString})`
+}