diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestMacroHelpers.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestMacroHelpers.res
index 752cc9c7..329f30bc 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestMacroHelpers.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestMacroHelpers.res
@@ -19,7 +19,7 @@ let testMacro_ = (
   let bindings = Bindings.fromArray(bindArray)
   tester(expr->T.toString, () =>
     expr
-    ->Macro.expandMacroCall(
+    ->Macro.expandMacroCallRs(
       bindings,
       ProjectAccessorsT.identityAccessors,
       Expression.reduceExpressionInProject,
@@ -44,6 +44,7 @@ let testMacroEval_ = (
       ProjectAccessorsT.identityAccessors,
       Expression.reduceExpressionInProject,
     )
+    ->Ok
     ->InternalExpressionValue.toStringResult
     ->expect
     ->toEqual(expectedValue)
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_arguments_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_arguments_test.res
index 29fa8249..957024cb 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_arguments_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_arguments_test.res
@@ -16,7 +16,7 @@ let checkArgumentsSourceCode = (aTypeSourceCode: string, sourceCode: string): re
 > => {
   let reducerFn = Expression.reduceExpressionInProject
   let rResult =
-    Expression.BackCompatible.parse(sourceCode)->Belt.Result.flatMap(expr =>
+    Expression.BackCompatible.parse(sourceCode)->Belt.Result.map(expr =>
       reducerFn(expr, Bindings.emptyBindings, ProjectAccessorsT.identityAccessors)
     )
   rResult->Belt.Result.flatMap(result =>
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_test.res
index fccff738..d5726d5d 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_Type/Reducer_Type_TypeChecker_test.res
@@ -19,7 +19,7 @@ let isTypeOfSourceCode = (aTypeSourceCode: string, sourceCode: string): result<
 > => {
   let reducerFn = Expression.reduceExpressionInProject
   let rResult =
-    Expression.BackCompatible.parse(sourceCode)->Belt.Result.flatMap(expr =>
+    Expression.BackCompatible.parse(sourceCode)->Belt.Result.map(expr =>
       reducerFn(expr, Bindings.emptyBindings, ProjectAccessorsT.identityAccessors)
     )
   rResult->Belt.Result.flatMap(result => TypeChecker.isTypeOf(aTypeSourceCode, result, reducerFn))
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
index f70aa934..f6b9ad77 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
@@ -56,7 +56,7 @@ describe("test exceptions", () => {
   testDescriptionEvalToBe(
     "javascript exception",
     "javascriptraise('div by 0')",
-    "Error(JS Exception: Error: 'div by 0')",
+    "Error(Error: 'div by 0')",
   )
   // testDescriptionEvalToBe(
   //   "rescript exception",
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Danger.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Danger.res
index 2a8b8773..2fcfcdaf 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Danger.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Danger.res
@@ -74,12 +74,11 @@ module Integration = {
           reducer,
         )
         let result = switch resultAsInternalExpression {
-        | Ok(IEvNumber(x)) => Ok(x)
-        | Error(_) =>
+        | IEvNumber(x) => Ok(x)
+        | _ =>
           Error(
             "Error 1 in Danger.integrate. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead",
           )
-        | _ => Error("Error 2 in Danger.integrate")
         }
         result
       }
@@ -143,7 +142,7 @@ module Integration = {
         }
       | Error(b) =>
         Error(
-          "Integration error 3 in Danger.integrate. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead." ++
+          "Integration error 2 in Danger.integrate. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead." ++
           "Original error: " ++
           b,
         )
@@ -309,14 +308,10 @@ module DiminishingReturns = {
               reducer,
             )
             switch resultAsInternalExpression {
-            | Ok(IEvNumber(x)) => Ok(x)
-            | Error(_) =>
-              Error(
-                "Error 1 in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead",
-              )
+            | IEvNumber(x) => Ok(x)
             | _ =>
               Error(
-                "Error 2 in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions",
+                "Error 1 in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions. It's possible that your function doesn't return a number, try definining auxiliaryFunction(x) = mean(yourFunction(x)) and integrate auxiliaryFunction instead",
               )
             }
           }
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res
index 63b7b3f4..1def1e36 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res
@@ -32,19 +32,17 @@ module Internals = {
     accessors: ProjectAccessorsT.t,
     eLambdaValue,
     reducer: ProjectReducerFnT.t,
-  ): result<ReducerInterface_InternalExpressionValue.t, Reducer_ErrorValue.errorValue> => {
-    let rMappedList = array->E.A.reduceReverse(Ok(list{}), (rAcc, elem) =>
-      rAcc->E.R.bind(_, acc => {
-        let rNewElem = Reducer_Expression_Lambda.doLambdaCall(
-          eLambdaValue,
-          list{elem},
-          (accessors: ProjectAccessorsT.t),
-          (reducer: ProjectReducerFnT.t),
-        )
-        rNewElem->E.R2.fmap(newElem => list{newElem, ...acc})
-      })
-    )
-    rMappedList->E.R2.fmap(mappedList => mappedList->Belt.List.toArray->Wrappers.evArray)
+  ): ReducerInterface_InternalExpressionValue.t => {
+    let mappedList = array->E.A.reduceReverse(list{}, (acc, elem) => {
+      let newElem = Reducer_Expression_Lambda.doLambdaCall(
+        eLambdaValue,
+        list{elem},
+        (accessors: ProjectAccessorsT.t),
+        (reducer: ProjectReducerFnT.t),
+      )
+      list{newElem, ...acc}
+    })
+    mappedList->Belt.List.toArray->Wrappers.evArray
   }
 
   let reduce = (
@@ -54,10 +52,8 @@ module Internals = {
     accessors: ProjectAccessorsT.t,
     reducer: ProjectReducerFnT.t,
   ) => {
-    aValueArray->E.A.reduce(Ok(initialValue), (rAcc, elem) =>
-      rAcc->E.R.bind(_, acc =>
-        Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list{acc, elem}, accessors, reducer)
-      )
+    aValueArray->E.A.reduce(initialValue, (acc, elem) =>
+      Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list{acc, elem}, accessors, reducer)
     )
   }
 
@@ -68,10 +64,8 @@ module Internals = {
     accessors: ProjectAccessorsT.t,
     reducer: ProjectReducerFnT.t,
   ) => {
-    aValueArray->Belt.Array.reduceReverse(Ok(initialValue), (rAcc, elem) =>
-      rAcc->Belt.Result.flatMap(acc =>
-        Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list{acc, elem}, accessors, reducer)
-      )
+    aValueArray->Belt.Array.reduceReverse(initialValue, (acc, elem) =>
+      Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list{acc, elem}, accessors, reducer)
     )
   }
 
@@ -81,25 +75,19 @@ module Internals = {
     accessors: ProjectAccessorsT.t,
     reducer: ProjectReducerFnT.t,
   ) => {
-    let rMappedList = aValueArray->Belt.Array.reduceReverse(Ok(list{}), (rAcc, elem) =>
-      rAcc->E.R.bind(_, acc => {
-        let rNewElem = Reducer_Expression_Lambda.doLambdaCall(
-          aLambdaValue,
-          list{elem},
-          accessors,
-          reducer,
-        )
-        rNewElem->E.R2.fmap(newElem => {
-          switch newElem {
-          | IEvBool(true) => list{elem, ...acc}
-          | _ => acc
-          }
-        })
-      })
-    )
-    let result =
-      rMappedList->E.R2.fmap(mappedList => mappedList->Belt.List.toArray->Wrappers.evArray)
-    result
+    let mappedList = aValueArray->Belt.Array.reduceReverse(list{}, (acc, elem) => {
+      let newElem = Reducer_Expression_Lambda.doLambdaCall(
+        aLambdaValue,
+        list{elem},
+        accessors,
+        reducer,
+      )
+      switch newElem {
+      | IEvBool(true) => list{elem, ...acc}
+      | _ => acc
+      }
+    })
+    mappedList->Belt.List.toArray->Wrappers.evArray
   }
 }
 
@@ -216,7 +204,7 @@ let library = [
         ~run=(inputs, _, accessors: ProjectAccessorsT.t, reducer) =>
           switch inputs {
           | [IEvArray(array), IEvLambda(lambda)] =>
-            Internals.map(array, accessors, lambda, reducer)->E.R2.errMap(_ => "Error!")
+            Ok(Internals.map(array, accessors, lambda, reducer))
           | _ => Error(impossibleError)
           },
         (),
@@ -236,9 +224,7 @@ let library = [
         ~run=(inputs, _, accessors: ProjectAccessorsT.t, reducer) =>
           switch inputs {
           | [IEvArray(array), initialValue, IEvLambda(lambda)] =>
-            Internals.reduce(array, initialValue, lambda, accessors, reducer)->E.R2.errMap(_ =>
-              "Error!"
-            )
+            Ok(Internals.reduce(array, initialValue, lambda, accessors, reducer))
           | _ => Error(impossibleError)
           },
         (),
@@ -258,13 +244,7 @@ let library = [
         ~run=(inputs, _, accessors: ProjectAccessorsT.t, reducer: ProjectReducerFnT.t) =>
           switch inputs {
           | [IEvArray(array), initialValue, IEvLambda(lambda)] =>
-            Internals.reduceReverse(
-              array,
-              initialValue,
-              lambda,
-              accessors,
-              reducer,
-            )->E.R2.errMap(_ => "Error!")
+            Ok(Internals.reduceReverse(array, initialValue, lambda, accessors, reducer))
           | _ => Error(impossibleError)
           },
         (),
@@ -284,7 +264,7 @@ let library = [
         ~run=(inputs, _, accessors: ProjectAccessorsT.t, reducer: ProjectReducerFnT.t) =>
           switch inputs {
           | [IEvArray(array), IEvLambda(lambda)] =>
-            Internals.filter(array, lambda, accessors, reducer)->E.R2.errMap(_ => "Error!")
+            Ok(Internals.filter(array, lambda, accessors, reducer))
           | _ => Error(impossibleError)
           },
         (),
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
index 0d950ce5..ccc9a4a4 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
@@ -37,7 +37,7 @@ module Internal = {
 
   let doLambdaCall = (aLambdaValue, list, environment, reducer) =>
     switch Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list, environment, reducer) {
-    | Ok(IEvNumber(f)) => Ok(f)
+    | IEvNumber(f) => Ok(f)
     | _ => Error(Operation.SampleMapNeedsNtoNFunction)
     }
 
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Sampleset.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Sampleset.res
index c3f56458..7d724a0f 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Sampleset.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Sampleset.res
@@ -16,7 +16,7 @@ module Internal = {
     reducer: ProjectReducerFnT.t,
   ) =>
     switch Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list, accessors, reducer) {
-    | Ok(IEvNumber(f)) => Ok(f)
+    | IEvNumber(f) => Ok(f)
     | _ => Error(Operation.SampleMapNeedsNtoNFunction)
     }
 
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 bec4a0da..985558e7 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
@@ -3,6 +3,7 @@ module BindingsReplacer = Reducer_Expression_BindingsReplacer
 module Continuation = ReducerInterface_Value_Continuation
 module ExpressionT = Reducer_Expression_T
 module ExternalLibrary = ReducerInterface.ExternalLibrary
+module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module Lambda = Reducer_Expression_Lambda
 module MathJs = Reducer_MathJs
 module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
@@ -111,7 +112,7 @@ let callInternal = (
   module SampleMap = {
     let doLambdaCall = (aLambdaValue, list) =>
       switch Lambda.doLambdaCall(aLambdaValue, list, accessors, reducer) {
-      | Ok(IEvNumber(f)) => Ok(f)
+      | IEvNumber(f) => Ok(f)
       | _ => Error(Operation.SampleMapNeedsNtoNFunction)
       }
 
@@ -201,13 +202,17 @@ let dispatch = (
   call: functionCall,
   accessors: ProjectAccessorsT.t,
   reducer: ProjectReducerFnT.t,
-): result<internalExpressionValue, errorValue> =>
+): internalExpressionValue =>
   try {
     let (fn, args) = call
     // There is a bug that prevents string match in patterns
     // So we have to recreate a copy of the string
-    ExternalLibrary.dispatch((Js.String.make(fn), args), accessors, reducer, callInternal)
+    ExternalLibrary.dispatch(
+      (Js.String.make(fn), args),
+      accessors,
+      reducer,
+      callInternal,
+    )->InternalExpressionValue.resultToValue
   } catch {
-  | Js.Exn.Error(obj) => REJavaScriptExn(Js.Exn.message(obj), Js.Exn.name(obj))->Error
-  | _ => RETodo("unhandled rescript exception")->Error
+  | exn => Reducer_ErrorValue.fromException(exn)->Reducer_ErrorValue.toException
   }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
index cee664bf..db77a0a2 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltInMacros.res
@@ -12,11 +12,9 @@ module ExpressionWithContext = Reducer_ExpressionWithContext
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
 module ProjectReducerFnT = ReducerProject_ReducerFn_T
-module Result = Belt.Result
 
 open Reducer_Expression_ExpressionBuilder
 
-type errorValue = ErrorValue.errorValue
 type expression = ExpressionT.expression
 type expressionWithContext = ExpressionWithContext.expressionWithContext
 
@@ -25,21 +23,15 @@ let dispatchMacroCall = (
   bindings: ExpressionT.bindings,
   accessors: ProjectAccessorsT.t,
   reduceExpression: ProjectReducerFnT.t,
-): result<expressionWithContext, errorValue> => {
+): expressionWithContext => {
   let useExpressionToSetBindings = (bindingExpr: expression, accessors, statement, newCode) => {
-    let rExternalBindingsValue = reduceExpression(bindingExpr, bindings, accessors)
+    let nameSpaceValue = reduceExpression(bindingExpr, bindings, accessors)
 
-    rExternalBindingsValue->Result.flatMap(nameSpaceValue => {
-      let newBindings = Bindings.fromExpressionValue(nameSpaceValue)
+    let newBindings = Bindings.fromExpressionValue(nameSpaceValue)
 
-      let rNewStatement = BindingsReplacer.replaceSymbols(newBindings, statement)
-      rNewStatement->Result.map(boundStatement =>
-        ExpressionWithContext.withContext(
-          newCode(newBindings->eModule, boundStatement),
-          newBindings,
-        )
-      )
-    })
+    let boundStatement = BindingsReplacer.replaceSymbols(newBindings, statement)
+
+    ExpressionWithContext.withContext(newCode(newBindings->eModule, boundStatement), newBindings)
   }
 
   let correspondingSetBindingsFn = (fnName: string): string =>
@@ -52,7 +44,7 @@ let dispatchMacroCall = (
     }
 
   let doBindStatement = (bindingExpr: expression, statement: expression, accessors) => {
-    let defaultStatement = ErrorValue.REAssignmentExpected->Error
+    let defaultStatement = ErrorValue.REAssignmentExpected
     switch statement {
     | ExpressionT.EList(list{ExpressionT.EValue(IEvCall(callName)), symbolExpr, statement}) => {
         let setBindingsFn = correspondingSetBindingsFn(callName)
@@ -62,17 +54,18 @@ let dispatchMacroCall = (
             boundStatement,
           ) => eFunction(setBindingsFn, list{newBindingsExpr, symbolExpr, boundStatement}))
         } else {
-          defaultStatement
+          defaultStatement->Reducer_ErrorValue.toException
         }
       }
-    | _ => defaultStatement
+    | _ => defaultStatement->Reducer_ErrorValue.toException
     }
   }
 
-  let doBindExpression = (bindingExpr: expression, statement: expression, accessors): result<
-    expressionWithContext,
-    errorValue,
-  > => {
+  let doBindExpression = (
+    bindingExpr: expression,
+    statement: expression,
+    accessors,
+  ): expressionWithContext => {
     let defaultStatement = () =>
       useExpressionToSetBindings(bindingExpr, accessors, statement, (
         _newBindingsExpr,
@@ -100,10 +93,11 @@ let dispatchMacroCall = (
     }
   }
 
-  let doBlock = (exprs: list<expression>, _bindings: ExpressionT.bindings, _accessors): result<
-    expressionWithContext,
-    errorValue,
-  > => {
+  let doBlock = (
+    exprs: list<expression>,
+    _bindings: ExpressionT.bindings,
+    _accessors,
+  ): expressionWithContext => {
     let exprsArray = Belt.List.toArray(exprs)
     let maxIndex = Js.Array2.length(exprsArray) - 1
     let newStatement = exprsArray->Js.Array2.reducei((acc, statement, index) =>
@@ -119,14 +113,14 @@ let dispatchMacroCall = (
         eBindStatement(acc, statement)
       }
     , eSymbol("undefined block"))
-    ExpressionWithContext.noContext(newStatement)->Ok
+    ExpressionWithContext.noContext(newStatement)
   }
 
   let doLambdaDefinition = (
     bindings: ExpressionT.bindings,
     parameters: array<string>,
     lambdaDefinition: ExpressionT.expression,
-  ) => ExpressionWithContext.noContext(eLambda(parameters, bindings, lambdaDefinition))->Ok
+  ) => ExpressionWithContext.noContext(eLambda(parameters, bindings, lambdaDefinition))
 
   let doTernary = (
     condition: expression,
@@ -134,25 +128,23 @@ let dispatchMacroCall = (
     ifFalse: expression,
     bindings: ExpressionT.bindings,
     accessors,
-  ): result<expressionWithContext, errorValue> => {
+  ): expressionWithContext => {
     let blockCondition = ExpressionBuilder.eBlock(list{condition})
-    let rCondition = reduceExpression(blockCondition, bindings, accessors)
-    rCondition->Result.flatMap(conditionValue =>
-      switch conditionValue {
-      | InternalExpressionValue.IEvBool(false) => {
-          let ifFalseBlock = eBlock(list{ifFalse})
-          ExpressionWithContext.withContext(ifFalseBlock, bindings)->Ok
-        }
-      | InternalExpressionValue.IEvBool(true) => {
-          let ifTrueBlock = eBlock(list{ifTrue})
-          ExpressionWithContext.withContext(ifTrueBlock, bindings)->Ok
-        }
-      | _ => REExpectedType("Boolean", "")->Error
+    let conditionValue = reduceExpression(blockCondition, bindings, accessors)
+    switch conditionValue {
+    | InternalExpressionValue.IEvBool(false) => {
+        let ifFalseBlock = eBlock(list{ifFalse})
+        ExpressionWithContext.withContext(ifFalseBlock, bindings)
       }
-    )
+    | InternalExpressionValue.IEvBool(true) => {
+        let ifTrueBlock = eBlock(list{ifTrue})
+        ExpressionWithContext.withContext(ifTrueBlock, bindings)
+      }
+    | _ => REExpectedType("Boolean", "")->Reducer_ErrorValue.toException
+    }
   }
 
-  let doEnvironment = (accessors: ProjectAccessorsT.t) => {
+  let doEnvironment = (accessors: ProjectAccessorsT.t): expressionWithContext => {
     let environment = accessors.environment
     let environmentPairs = [
       ("sampleCount", environment.sampleCount->Js.Int.toFloat->InternalExpressionValue.IEvNumber),
@@ -162,7 +154,7 @@ let dispatchMacroCall = (
       ),
     ]
     let environmentMap = Belt.Map.String.fromArray(environmentPairs)
-    ExpressionWithContext.noContext(ExpressionBuilder.eRecord(environmentMap))->Ok
+    ExpressionWithContext.noContext(ExpressionBuilder.eRecord(environmentMap))
   }
 
   let doWithEnvironmentSampleCount = (
@@ -170,27 +162,25 @@ let dispatchMacroCall = (
     expr: expression,
     bindings: ExpressionT.bindings,
     accessors: ProjectAccessorsT.t,
-  ) => {
+  ): expressionWithContext => {
     let blockSampleCount = ExpressionBuilder.eBlock(list{sampleCountExpr})
-    let rSampleCount = reduceExpression(blockSampleCount, bindings, accessors)
-    rSampleCount->Result.flatMap(sampleCountValue =>
-      switch sampleCountValue {
-      | InternalExpressionValue.IEvNumber(sampleCount) => {
-          let newEnvironment = {...accessors.environment, sampleCount: Js.Math.floor(sampleCount)}
-          let newAccessors = {...accessors, environment: newEnvironment}
-          reduceExpression(expr, bindings, newAccessors)->Belt.Result.map(value =>
-            value->ExpressionT.EValue->ExpressionWithContext.noContext
-          )
-        }
-      | _ => REExpectedType("Number", "")->Error
+    let sampleCount = reduceExpression(blockSampleCount, bindings, accessors)
+    switch sampleCount {
+    | InternalExpressionValue.IEvNumber(sampleCount) => {
+        let newEnvironment = {...accessors.environment, sampleCount: Js.Math.floor(sampleCount)}
+        let newAccessors = {...accessors, environment: newEnvironment}
+        reduceExpression(expr, bindings, newAccessors)
+        ->ExpressionT.EValue
+        ->ExpressionWithContext.noContext
       }
-    )
+    | _ => REExpectedType("Number", "")->Reducer_ErrorValue.toException
+    }
   }
-
-  let expandExpressionList = (aList, bindings: ExpressionT.bindings, accessors): result<
-    expressionWithContext,
-    errorValue,
-  > =>
+  let expandExpressionList = (
+    aList,
+    bindings: ExpressionT.bindings,
+    accessors,
+  ): expressionWithContext =>
     switch aList {
     | list{
         ExpressionT.EValue(IEvCall("$$_bindStatement_$$")),
@@ -227,11 +217,11 @@ let dispatchMacroCall = (
         sampleCountExpr,
       } =>
       doWithEnvironmentSampleCount(sampleCountExpr, expr, bindings, accessors)
-    | _ => ExpressionWithContext.noContext(ExpressionT.EList(aList))->Ok
+    | _ => ExpressionWithContext.noContext(ExpressionT.EList(aList))
     }
 
   switch macroExpression {
   | EList(aList) => expandExpressionList(aList, bindings, accessors)
-  | _ => ExpressionWithContext.noContext(macroExpression)->Ok
+  | _ => ExpressionWithContext.noContext(macroExpression)
   }
 }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
index 46da2216..b6baeaf5 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
@@ -26,6 +26,8 @@ type errorValue =
 
 type t = errorValue
 
+exception ErrorException(errorValue)
+
 let errorToString = err =>
   switch err {
   | REArityError(_oFnName, arity, usedArity) =>
@@ -62,3 +64,20 @@ let errorToString = err =>
   | RENeedToRun => "Need to run"
   | REOther(msg) => `Error: ${msg}`
   }
+
+let fromException = exn =>
+  switch exn {
+  | ErrorException(e) => e
+  | Js.Exn.Error(e) =>
+    switch Js.Exn.message(e) {
+    | Some(message) => REOther(message)
+    | None =>
+      switch Js.Exn.name(e) {
+      | Some(name) => REOther(name)
+      | None => REOther("Unknown error")
+      }
+    }
+  | _e => REOther("Unknown error")
+  }
+
+let toException = (errorValue: t) => raise(ErrorException(errorValue))
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 614ba3a8..e3fdf168 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
@@ -21,10 +21,10 @@ let rec reduceExpressionInProject = (
   expression: t,
   continuation: T.bindings,
   accessors: ProjectAccessorsT.t,
-): result<InternalExpressionValue.t, 'e> => {
-  // `reduce: ${T.toString(expression)}`->Js.log
+): InternalExpressionValue.t => {
+  // Js.log(`reduce: ${T.toString(expression)} bindings: ${bindings->Bindings.toString}`)
   switch expression {
-  | T.EValue(value) => value->Ok
+  | T.EValue(value) => value
   | T.EList(list) =>
     switch list {
     | list{EValue(IEvCall(fName)), ..._args} =>
@@ -41,20 +41,12 @@ and reduceExpressionList = (
   expressions: list<t>,
   continuation: T.bindings,
   accessors: ProjectAccessorsT.t,
-): result<InternalExpressionValue.t, 'e> => {
-  let racc: result<
-    list<InternalExpressionValue.t>,
-    'e,
-  > = expressions->Belt.List.reduceReverse(Ok(list{}), (racc, each: t) =>
-    racc->Result.flatMap(acc => {
-      each
-      ->reduceExpressionInProject(continuation, accessors)
-      ->Result.map(newNode => {
-        acc->Belt.List.add(newNode)
-      })
-    })
-  )
-  racc->Result.flatMap(acc => acc->reduceValueList(accessors))
+): InternalExpressionValue.t => {
+  let acc: list<InternalExpressionValue.t> =
+    expressions->Belt.List.reduceReverse(list{}, (acc, each: t) =>
+      acc->Belt.List.add(each->reduceExpressionInProject(continuation, accessors))
+    )
+  acc->reduceValueList(accessors)
 }
 
 /*
@@ -63,48 +55,34 @@ and reduceExpressionList = (
 and reduceValueList = (
   valueList: list<InternalExpressionValue.t>,
   accessors: ProjectAccessorsT.t,
-): result<InternalExpressionValue.t, 'e> =>
+): InternalExpressionValue.t =>
   switch valueList {
   | list{IEvCall(fName), ...args} => {
-      let rCheckedArgs = switch fName {
-      | "$_setBindings_$" | "$_setTypeOfBindings_$" | "$_setTypeAliasBindings_$" => args->Ok
+      let checkedArgs = switch fName {
+      | "$_setBindings_$" | "$_setTypeOfBindings_$" | "$_setTypeAliasBindings_$" => args
       | _ => args->Lambda.checkIfReduced
       }
 
-      rCheckedArgs->Result.flatMap(checkedArgs =>
-        (fName, checkedArgs->Belt.List.toArray)->BuiltIn.dispatch(
-          accessors,
-          reduceExpressionInProject,
-        )
+      (fName, checkedArgs->Belt.List.toArray)->BuiltIn.dispatch(
+        accessors,
+        reduceExpressionInProject,
       )
     }
   | list{IEvLambda(_)} =>
     // TODO: remove on solving issue#558
-    valueList
-    ->Lambda.checkIfReduced
-    ->Result.flatMap(reducedValueList =>
-      reducedValueList->Belt.List.toArray->InternalExpressionValue.IEvArray->Ok
-    )
+    valueList->Lambda.checkIfReduced->Belt.List.toArray->InternalExpressionValue.IEvArray
   | list{IEvLambda(lambdaCall), ...args} =>
     args
     ->Lambda.checkIfReduced
-    ->Result.flatMap(checkedArgs =>
-      Lambda.doLambdaCall(lambdaCall, checkedArgs, accessors, reduceExpressionInProject)
-    )
-
-  | _ =>
-    valueList
-    ->Lambda.checkIfReduced
-    ->Result.flatMap(reducedValueList =>
-      reducedValueList->Belt.List.toArray->InternalExpressionValue.IEvArray->Ok
-    )
+    ->Lambda.doLambdaCall(lambdaCall, _, accessors, reduceExpressionInProject)
+  | _ => valueList->Lambda.checkIfReduced->Belt.List.toArray->InternalExpressionValue.IEvArray
   }
 
 let reduceReturningBindings = (
   expression: t,
   continuation: T.bindings,
   accessors: ProjectAccessorsT.t,
-): (result<InternalExpressionValue.t, 'e>, T.bindings) => {
+): (InternalExpressionValue.t, T.bindings) => {
   let states = accessors.states
   let result = reduceExpressionInProject(expression, continuation, accessors)
   (result, states.continuation)
@@ -118,7 +96,11 @@ module BackCompatible = {
 
   let evaluate = (expression: t): result<InternalExpressionValue.t, errorValue> => {
     let accessors = ProjectAccessorsT.identityAccessors
-    expression->reduceExpressionInProject(accessors.stdLib, accessors)
+    try {
+      expression->reduceExpressionInProject(accessors.stdLib, accessors)->Ok
+    } catch {
+    | exn => Reducer_ErrorValue.fromException(exn)->Error
+    }
   }
 
   let evaluateString = (peggyCode: string): result<InternalExpressionValue.t, errorValue> =>
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
index 808a2dcd..539585b4 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_ExpressionWithContext.res
@@ -18,12 +18,14 @@ type expressionWithContext =
   | ExpressionWithContext(expression, context)
   | ExpressionNoContext(expression)
 
+type t = expressionWithContext
+
 let callReducer = (
   expressionWithContext: expressionWithContext,
   bindings: bindings,
   accessors: ProjectAccessorsT.t,
   reducer: ProjectReducerFnT.t,
-): result<internalExpressionValue, errorValue> => {
+): internalExpressionValue => {
   switch expressionWithContext {
   | ExpressionNoContext(expr) =>
     // Js.log(`callReducer: bindings ${Bindings.toString(bindings)} expr ${ExpressionT.toString(expr)}`)
@@ -51,3 +53,10 @@ let toStringResult = rExpressionWithContext =>
   | Ok(expressionWithContext) => `Ok(${toString(expressionWithContext)})`
   | Error(errorValue) => ErrorValue.errorToString(errorValue)
   }
+
+let resultToValue = (rExpressionWithContext: result<t, errorValue>): t => {
+  switch rExpressionWithContext {
+  | Ok(expressionWithContext) => expressionWithContext
+  | Error(errorValue) => ErrorValue.toException(errorValue)
+  }
+}
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_BindingsReplacer.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_BindingsReplacer.res
index 6e38f833..f1bf0135 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_BindingsReplacer.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_BindingsReplacer.res
@@ -1,7 +1,6 @@
 module ErrorValue = Reducer_ErrorValue
 module ExpressionT = Reducer_Expression_T
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
-module Result = Belt.Result
 module Bindings = Reducer_Bindings
 
 type errorValue = Reducer_ErrorValue.errorValue
@@ -10,19 +9,15 @@ type internalExpressionValue = InternalExpressionValue.t
 
 let isMacroName = (fName: string): bool => fName->Js.String2.startsWith("$$")
 
-let rec replaceSymbols = (bindings: ExpressionT.bindings, expression: expression): result<
-  expression,
-  errorValue,
-> =>
+let rec replaceSymbols = (bindings: ExpressionT.bindings, expression: expression): expression =>
   switch expression {
-  | ExpressionT.EValue(value) =>
-    replaceSymbolOnValue(bindings, value)->Result.map(evValue => evValue->ExpressionT.EValue)
+  | ExpressionT.EValue(value) => replaceSymbolOnValue(bindings, value)->ExpressionT.EValue
   | ExpressionT.EList(list) =>
     switch list {
     | list{EValue(IEvCall(fName)), ..._args} =>
       switch isMacroName(fName) {
       // A macro reduces itself so we dont dive in it
-      | true => expression->Ok
+      | true => expression
       | false => replaceSymbolsOnExpressionList(bindings, list)
       }
     | _ => replaceSymbolsOnExpressionList(bindings, list)
@@ -30,23 +25,21 @@ let rec replaceSymbols = (bindings: ExpressionT.bindings, expression: expression
   }
 
 and replaceSymbolsOnExpressionList = (bindings, list) => {
-  let racc = list->Belt.List.reduceReverse(Ok(list{}), (racc, each: expression) =>
-    racc->Result.flatMap(acc => {
-      replaceSymbols(bindings, each)->Result.flatMap(newNode => {
-        acc->Belt.List.add(newNode)->Ok
-      })
-    })
-  )
-  racc->Result.map(acc => acc->ExpressionT.EList)
+  let racc =
+    list->Belt.List.reduceReverse(list{}, (acc, each: expression) =>
+      replaceSymbols(bindings, each)->Belt.List.add(acc, _)
+    )
+  ExpressionT.EList(racc)
 }
 and replaceSymbolOnValue = (bindings, evValue: internalExpressionValue) =>
   switch evValue {
-  | IEvSymbol(symbol) => Bindings.getWithDefault(bindings, symbol, evValue)->Ok
+  | IEvSymbol(symbol) => Bindings.getWithDefault(bindings, symbol, evValue)
   | IEvCall(symbol) => Bindings.getWithDefault(bindings, symbol, evValue)->checkIfCallable
-  | _ => evValue->Ok
+  | _ => evValue
   }
 and checkIfCallable = (evValue: internalExpressionValue) =>
   switch evValue {
-  | IEvCall(_) | IEvLambda(_) => evValue->Ok
-  | _ => ErrorValue.RENotAFunction(InternalExpressionValue.toString(evValue))->Error
+  | IEvCall(_) | IEvLambda(_) => evValue
+  | _ =>
+    ErrorValue.RENotAFunction(InternalExpressionValue.toString(evValue))->ErrorValue.toException
   }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
index 5ab7761d..aa0745ae 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Lambda.res
@@ -23,26 +23,24 @@ let checkArity = (
     let argsLength = Belt.List.length(args)
     let parametersLength = Js.Array2.length(lambdaValue.parameters)
     if argsLength !== parametersLength {
-      ErrorValue.REArityError(None, parametersLength, argsLength)->Error
+      ErrorValue.REArityError(None, parametersLength, argsLength)->ErrorValue.toException
     } else {
-      args->Ok
+      args
     }
   }
   let exprOrFFI = castInternalCodeToExpression(lambdaValue.body)
   switch exprOrFFI {
   | NotFFI(_) => reallyCheck
-  | FFI(_) => args->Ok
+  | FFI(_) => args
   }
 }
 
 let checkIfReduced = (args: list<internalExpressionValue>) =>
-  args->Belt.List.reduceReverse(Ok(list{}), (rAcc, arg) =>
-    rAcc->Result.flatMap(acc =>
-      switch arg {
-      | IEvSymbol(symbol) => ErrorValue.RESymbolNotFound(symbol)->Error
-      | _ => list{arg, ...acc}->Ok
-      }
-    )
+  args->Belt.List.reduceReverse(list{}, (acc, arg) =>
+    switch arg {
+    | IEvSymbol(symbol) => ErrorValue.RESymbolNotFound(symbol)->ErrorValue.toException
+    | _ => list{arg, ...acc}
+    }
   )
 
 let caseNotFFI = (
@@ -63,7 +61,10 @@ let caseNotFFI = (
 }
 
 let caseFFI = (ffiFn: ExpressionT.ffiFn, args, accessors: ProjectAccessorsT.t) => {
-  ffiFn(args->Belt.List.toArray, accessors.environment)
+  switch ffiFn(args->Belt.List.toArray, accessors.environment) {
+  | Ok(value) => value
+  | Error(value) => value->ErrorValue.toException
+  }
 }
 
 let applyParametersToLambda = (
@@ -71,16 +72,13 @@ let applyParametersToLambda = (
   args,
   accessors: ProjectAccessorsT.t,
   reducer: ProjectReducerFnT.t,
-): result<internalExpressionValue, 'e> => {
-  checkArity(lambdaValue, args)->Result.flatMap(args =>
-    checkIfReduced(args)->Result.flatMap(args => {
-      let exprOrFFI = castInternalCodeToExpression(lambdaValue.body)
-      switch exprOrFFI {
-      | NotFFI(expr) => caseNotFFI(lambdaValue, expr, args, accessors, reducer)
-      | FFI(ffiFn) => caseFFI(ffiFn, args, accessors)
-      }
-    })
-  )
+): internalExpressionValue => {
+  let args = checkArity(lambdaValue, args)->checkIfReduced
+  let exprOrFFI = castInternalCodeToExpression(lambdaValue.body)
+  switch exprOrFFI {
+  | NotFFI(expr) => caseNotFFI(lambdaValue, expr, args, accessors, reducer)
+  | FFI(ffiFn) => caseFFI(ffiFn, args, accessors)
+  }
 }
 
 let doLambdaCall = (
@@ -95,7 +93,7 @@ let foreignFunctionInterface = (
   argArray: array<internalExpressionValue>,
   accessors: ProjectAccessorsT.t,
   reducer: ProjectReducerFnT.t,
-): result<internalExpressionValue, Reducer_ErrorValue.errorValue> => {
+): internalExpressionValue => {
   let args = argArray->Belt.List.fromArray
   applyParametersToLambda(lambdaValue, args, accessors, reducer)
 }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Macro.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Macro.res
index 003d3170..11a7cb0b 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Macro.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_Macro.res
@@ -10,32 +10,34 @@ type expression = ExpressionT.expression
 type internalExpressionValue = InternalExpressionValue.t
 type expressionWithContext = ExpressionWithContext.expressionWithContext
 
-let expandMacroCall = (
+let expandMacroCallRs = (
   macroExpression: expression,
   bindings: ExpressionT.bindings,
   accessors: ProjectAccessorsT.t,
   reduceExpression: ProjectReducerFnT.t,
 ): result<expressionWithContext, 'e> =>
-  Reducer_Dispatch_BuiltInMacros.dispatchMacroCall(
-    macroExpression,
-    bindings,
-    accessors,
-    reduceExpression,
-  )
+  try {
+    Reducer_Dispatch_BuiltInMacros.dispatchMacroCall(
+      macroExpression,
+      bindings,
+      accessors,
+      reduceExpression,
+    )->Ok
+  } catch {
+  | exn => Reducer_ErrorValue.fromException(exn)->Error
+  }
 
 let doMacroCall = (
   macroExpression: expression,
   bindings: ExpressionT.bindings,
   accessors: ProjectAccessorsT.t,
   reduceExpression: ProjectReducerFnT.t,
-): result<internalExpressionValue, 'e> =>
-  expandMacroCall(
+): internalExpressionValue =>
+  Reducer_Dispatch_BuiltInMacros.dispatchMacroCall(
     macroExpression,
     bindings,
     (accessors: ProjectAccessorsT.t),
     (reduceExpression: ProjectReducerFnT.t),
-  )->Result.flatMap(expressionWithContext =>
-    ExpressionWithContext.callReducer(expressionWithContext, bindings, accessors, reduceExpression)
-  )
+  )->ExpressionWithContext.callReducer(bindings, accessors, reduceExpression)
 
 let isMacroName = (fName: string): bool => fName->Js.String2.startsWith("$$")
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res
index 61f723df..be2755fe 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_T.res
@@ -82,3 +82,9 @@ type optionFfiFnReturningResult = (
 type expressionOrFFI =
   | NotFFI(expression)
   | FFI(ffiFn)
+
+let resultToValue = (rExpression: result<t, Reducer_ErrorValue.t>): t =>
+  switch rExpression {
+  | Ok(expression) => expression
+  | Error(errorValue) => Reducer_ErrorValue.toException(errorValue)
+  }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_Compile.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_Compile.res
index 79153801..b2e0be9b 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_Compile.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_Compile.res
@@ -15,16 +15,12 @@ let ievFromTypeExpression = (
   let sourceCode = `type ${sIndex}=${typeExpressionSourceCode}`
   Reducer_Expression.BackCompatible.parse(sourceCode)->Belt.Result.flatMap(expr => {
     let accessors = ProjectAccessorsT.identityAccessors
-    let result = reducerFn(expr, Bindings.emptyBindings, accessors)
+    let _result = reducerFn(expr, Bindings.emptyBindings, accessors)
     let nameSpace = accessors.states.continuation
 
-    switch result {
-    | Ok(_) =>
-      switch Bindings.getType(nameSpace, sIndex) {
-      | Some(value) => value->Ok
-      | None => raise(Reducer_Exception.ImpossibleException("Reducer_Type_Compile-none"))
-      }
-    | err => err
+    switch Bindings.getType(nameSpace, sIndex) {
+    | Some(value) => value->Ok
+    | None => raise(Reducer_Exception.ImpossibleException("Reducer_Type_Compile-none"))
     }
   })
 }
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_InternalExpressionValue.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_InternalExpressionValue.res
index 34eb6f40..5531cbdf 100644
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_InternalExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_InternalExpressionValue.res
@@ -244,3 +244,9 @@ let nameSpaceGet = (nameSpace: nameSpace, key: string): option<t> => {
   let NameSpace(container) = nameSpace
   container->Belt.Map.String.get(key)
 }
+
+let resultToValue = (rExpression: result<t, Reducer_ErrorValue.t>): t =>
+  switch rExpression {
+  | Ok(expression) => expression
+  | Error(errorValue) => Reducer_ErrorValue.toException(errorValue)
+  }
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
index 8eb915de..7676ddef 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
@@ -183,17 +183,6 @@ let buildExpression = (this: t): t => {
   }
 }
 
-let wrappedReducer = (
-  rExpression: T.expressionArgumentType,
-  aContinuation: T.continuation,
-  accessors: ProjectAccessorsT.t,
-): T.resultArgumentType => {
-  Belt.Result.flatMap(
-    rExpression,
-    Reducer_Expression.reduceExpressionInProject(_, aContinuation, accessors),
-  )
-}
-
 let doBuildResult = (
   this: t,
   aContinuation: T.continuation,
@@ -202,9 +191,12 @@ let doBuildResult = (
   this
   ->getExpression
   ->Belt.Option.map(
-    Belt.Result.flatMap(
-      _,
-      Reducer_Expression.reduceExpressionInProject(_, aContinuation, accessors),
+    Belt.Result.flatMap(_, expression =>
+      try {
+        Reducer_Expression.reduceExpressionInProject(expression, aContinuation, accessors)->Ok
+      } catch {
+      | exn => Reducer_ErrorValue.fromException(exn)->Error
+      }
     ),
   )
 
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ReducerFn_T.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ReducerFn_T.res
index 0b401fcb..2dc926be 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ReducerFn_T.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ReducerFn_T.res
@@ -2,8 +2,4 @@ module ExpressionT = Reducer_Expression_T
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
 
-type t = (
-  ExpressionT.t,
-  ExpressionT.bindings,
-  ProjectAccessorsT.t,
-) => result<InternalExpressionValue.t, Reducer_ErrorValue.errorValue>
+type t = (ExpressionT.t, ExpressionT.bindings, ProjectAccessorsT.t) => InternalExpressionValue.t