diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_TestHelpers.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_TestHelpers.res
index 65d87565..e30d3274 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_TestHelpers.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_Peggy/Reducer_Peggy_TestHelpers.res
@@ -22,9 +22,7 @@ let expectExpressionToBe = (expr, answer, ~v="_", ()) => {
   } else {
     let a2 =
       rExpr
-      ->E.R2.errMap(e =>
-        e->Reducer_ErrorValue.fromParseError->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue
-      )
+      ->E.R2.errMap(e => e->SqError.Message.fromParseError->SqError.Error.fromMessage)
       ->Result.flatMap(expr => Expression.BackCompatible.evaluate(expr))
       ->Reducer_Value.toStringResultOkless
     (a1, a2)->expect->toEqual((answer, v))
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
index 43de902e..efff179e 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
@@ -1,4 +1,3 @@
-module ErrorValue = Reducer_ErrorValue
 module Expression = Reducer_Expression
 module ExpressionT = Reducer_Expression_T
 
@@ -9,7 +8,7 @@ let unwrapRecord = rValue =>
   rValue->Belt.Result.flatMap(value =>
     switch value {
     | Reducer_T.IEvRecord(aRecord) => Ok(aRecord)
-    | _ => ErrorValue.RETodo("TODO: Internal bindings must be returned")->Error
+    | _ => SqError.Message.RETodo("TODO: Internal bindings must be returned")->Error
     }
   )
 
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
index 49180135..0697d239 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
@@ -70,7 +70,7 @@ describe("test exceptions", () => {
   testDescriptionEvalToBe(
     "javascript exception",
     "javascriptraise('div by 0')",
-    "Error(Error: 'div by 0')",
+    "Error(JS Exception: Error: 'div by 0')",
   )
   // testDescriptionEvalToBe(
   //   "rescript exception",
diff --git a/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_includes_test.res b/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_includes_test.res
index a6b35ec4..6c6d46fe 100644
--- a/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_includes_test.res
+++ b/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_includes_test.res
@@ -25,7 +25,7 @@ x=1`,
     let mainIncludes = Project.getIncludes(project, "main")
     switch mainIncludes {
     | Ok(includes) => expect(includes) == ["common"]
-    | Error(error) => fail(error->Reducer_ErrorValue.errorValueToString)
+    | Error(error) => fail(error->SqError.Message.toString)
     }
   })
   test("past chain", () => {
@@ -60,7 +60,7 @@ x=1`,
     let mainIncludes = Project.getIncludes(project, "main")
     switch mainIncludes {
     | Ok(includes) => expect(includes) == ["common", "myModule"]
-    | Error(error) => fail(error->Reducer_ErrorValue.errorValueToString)
+    | Error(error) => fail(error->SqError.Message.toString)
     }
   })
 
@@ -99,7 +99,7 @@ x=1`,
     let mainIncludes = Project.getIncludes(project, "main")
     switch mainIncludes {
     | Ok(includes) => expect(includes) == ["common", "common2", "myModule"]
-    | Error(error) => fail(error->Reducer_ErrorValue.errorValueToString)
+    | Error(error) => fail(error->SqError.Message.toString)
     }
   })
   test("direct past chain", () => {
diff --git a/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_3_includes_test.res b/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_3_includes_test.res
index 995ce4d3..bd06c481 100644
--- a/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_3_includes_test.res
+++ b/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_3_includes_test.res
@@ -36,7 +36,7 @@ Here we will finally proceed to a real life scenario. */
       /* Parse includes has set the includes */
       switch project->Project.getIncludes("main") {
       | Ok(includes) => includes->expect == ["common"]
-      | Error(err) => err->Reducer_ErrorValue.errorValueToString->fail
+      | Error(err) => err->SqError.Message.toString->fail
       }
       /* If the includes cannot be parsed then you get a syntax error.
       Otherwise you get the includes.
@@ -85,7 +85,7 @@ Here we will finally proceed to a real life scenario. */
           let rIncludes = project->Project.getIncludes(sourceName)
           switch rIncludes {
           /* Maybe there is an include syntax error */
-          | Error(err) => err->Reducer_ErrorValue.errorValueToString->Js.Exn.raiseError
+          | Error(err) => err->SqError.Message.toString->Js.Exn.raiseError
 
           | Ok(includes) =>
             includes->Belt.Array.forEach(newIncludeName => {
@@ -169,7 +169,7 @@ Here we will finally proceed to a real life scenario. */
     test("getIncludes", () => {
       switch Project.getIncludes(project, "main") {
       | Ok(includes) => includes->expect == ["common"]
-      | Error(err) => err->Reducer_ErrorValue.errorValueToString->fail
+      | Error(err) => err->SqError.Message.toString->fail
       }
     })
   })
diff --git a/packages/squiggle-lang/src/js/SqError.ts b/packages/squiggle-lang/src/js/SqError.ts
index c0c509b4..ea21dc11 100644
--- a/packages/squiggle-lang/src/js/SqError.ts
+++ b/packages/squiggle-lang/src/js/SqError.ts
@@ -1,13 +1,13 @@
-import * as RSErrorValue from "../rescript/ForTS/ForTS_Reducer_ErrorValue.gen";
+import * as RSError from "../rescript/ForTS/ForTS_SqError.gen";
 
 export class SqError {
-  constructor(private _value: RSErrorValue.reducerError) {}
+  constructor(private _value: RSError.error) {}
 
   toString() {
-    return RSErrorValue.toString(this._value);
+    return RSError.toString(this._value);
   }
 
   static createOtherError(v: string) {
-    return new SqError(RSErrorValue.createOtherError(v));
+    return new SqError(RSError.createOtherError(v));
   }
 }
diff --git a/packages/squiggle-lang/src/js/SqProject.ts b/packages/squiggle-lang/src/js/SqProject.ts
index 22f2f78a..30d8b245 100644
--- a/packages/squiggle-lang/src/js/SqProject.ts
+++ b/packages/squiggle-lang/src/js/SqProject.ts
@@ -1,15 +1,12 @@
 import * as RSProject from "../rescript/ForTS/ForTS_ReducerProject.gen";
-import {
-  reducerError,
-  reducerErrorValue,
-  attachEmptyStackTraceToErrorValue,
-} from "../rescript/ForTS/ForTS_Reducer_ErrorValue.gen";
+import * as RSError from "../rescript/ForTS/ForTS_SqError.gen";
 import { environment } from "../rescript/ForTS/ForTS_Distribution/ForTS_Distribution_Environment.gen";
 import { SqError } from "./SqError";
 import { SqRecord } from "./SqRecord";
 import { wrapValue } from "./SqValue";
 import { resultMap2 } from "./types";
 import { SqValueLocation } from "./SqValueLocation";
+import { errorFromMessage } from "../rescript/ForTS/ForTS_SqError.gen";
 
 export class SqProject {
   constructor(private _value: RSProject.reducerProject) {}
@@ -54,8 +51,7 @@ export class SqProject {
     return resultMap2(
       RSProject.getIncludes(this._value, sourceId),
       (a) => a,
-      (v: reducerErrorValue) =>
-        new SqError(attachEmptyStackTraceToErrorValue(v))
+      (v: RSError.errorMessage) => new SqError(errorFromMessage(v))
     );
   }
 
@@ -109,7 +105,7 @@ export class SqProject {
             items: [],
           })
         ),
-      (v: reducerError) => new SqError(v)
+      (v: RSError.error) => new SqError(v)
     );
   }
 
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Builtin.res b/packages/squiggle-lang/src/rescript/FR/FR_Builtin.res
index 84e6a50f..3e7a9e8b 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Builtin.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Builtin.res
@@ -5,7 +5,7 @@ let nameSpace = "" // no namespaced versions
 
 type simpleDefinition = {
   inputs: array<frType>,
-  fn: array<Reducer_T.value> => result<Reducer_T.value, errorValue>,
+  fn: array<Reducer_T.value> => result<Reducer_T.value, errorMessage>,
 }
 
 let makeFnMany = (name: string, definitions: array<simpleDefinition>) =>
@@ -22,7 +22,7 @@ let makeFnMany = (name: string, definitions: array<simpleDefinition>) =>
 let makeFn = (
   name: string,
   inputs: array<frType>,
-  fn: array<Reducer_T.value> => result<Reducer_T.value, errorValue>,
+  fn: array<Reducer_T.value> => result<Reducer_T.value, errorMessage>,
 ) => makeFnMany(name, [{inputs: inputs, fn: fn}])
 
 let library = [
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Danger.res b/packages/squiggle-lang/src/rescript/FR/FR_Danger.res
index 7767f8c1..0474c1f4 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Danger.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Danger.res
@@ -77,7 +77,7 @@ module Integration = {
         | Reducer_T.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"->Reducer_ErrorValue.REOther,
+            "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"->SqError.Message.REOther,
           )
         }
         result
@@ -143,8 +143,8 @@ module Integration = {
       | Error(b) =>
         ("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->Reducer_ErrorValue.errorValueToString)
-        ->Reducer_ErrorValue.REOther
+        b->SqError.Message.toString)
+        ->SqError.Message.REOther
         ->Error
       }
       result
@@ -169,7 +169,7 @@ module Integration = {
             let result = switch inputs {
             | [_, _, _, IEvNumber(0.0)] =>
               "Integration error 4 in Danger.integrate: Increment can't be 0."
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             | [
                 IEvLambda(aLambda),
@@ -187,7 +187,7 @@ module Integration = {
               )
             | _ =>
               Error(
-                Reducer_ErrorValue.REOther(
+                SqError.Message.REOther(
                   "Integration error 5 in Danger.integrate. Remember that inputs are (function, number (min), number (max), number(increment))",
                 ),
               )
@@ -213,7 +213,7 @@ module Integration = {
             let result = switch inputs {
             | [_, _, _, IEvNumber(0.0)] =>
               "Integration error in Danger.integrate: Increment can't be 0."
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             | [IEvLambda(aLambda), IEvNumber(min), IEvNumber(max), IEvNumber(epsilon)] =>
               Helpers.integrateFunctionBetweenWithNumIntegrationPoints(
@@ -225,11 +225,11 @@ module Integration = {
                 reducer,
               )->E.R2.errMap(b =>
                 ("Integration error 7 in Danger.integrate. Something went wrong along the way: " ++
-                b->Reducer_ErrorValue.errorValueToString)->Reducer_ErrorValue.REOther
+                b->SqError.Message.toString)->SqError.Message.REOther
               )
             | _ =>
               "Integration error 8 in Danger.integrate. Remember that inputs are (function, number (min), number (max), number(increment))"
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             }
             result
@@ -246,7 +246,7 @@ module DiminishingReturns = {
   module Helpers = {
     type diminishingReturnsAccumulatorInner = {
       optimalAllocations: array<float>,
-      currentMarginalReturns: result<array<float>, errorValue>,
+      currentMarginalReturns: result<array<float>, errorMessage>,
     }
     let findBiggestElementIndex = (xs: array<float>) =>
       E.A.reducei(xs, 0, (acc, newElement, index) => {
@@ -255,7 +255,7 @@ module DiminishingReturns = {
         | false => acc
         }
       })
-    type diminishingReturnsAccumulator = result<diminishingReturnsAccumulatorInner, errorValue>
+    type diminishingReturnsAccumulator = result<diminishingReturnsAccumulatorInner, errorMessage>
     // TODO: This is so complicated, it probably should be its own file. It might also make sense to have it work in Rescript directly, taking in a function rather than a reducer; then something else can wrap that function in the reducer/lambdas/environment.
     /*
     The key idea for this function is that 
@@ -290,19 +290,19 @@ module DiminishingReturns = {
       ) {
       | (false, _, _, _) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, number of functions should be greater than 1."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, number of functions should be greater than 1."->SqError.Message.REOther,
         )
       | (_, false, _, _) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, funds should be greater than 0."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, funds should be greater than 0."->SqError.Message.REOther,
         )
       | (_, _, false, _) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be greater than 0."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be greater than 0."->SqError.Message.REOther,
         )
       | (_, _, _, false) =>
         Error(
-          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be smaller than funds amount."->Reducer_ErrorValue.REOther,
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be smaller than funds amount."->SqError.Message.REOther,
         )
       | (true, true, true, true) => {
           let applyFunctionAtPoint = (lambda, point: float) => {
@@ -318,7 +318,7 @@ module DiminishingReturns = {
             | Reducer_T.IEvNumber(x) => Ok(x)
             | _ =>
               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"->Reducer_ErrorValue.REOther,
+                "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"->SqError.Message.REOther,
               )
             }
           }
@@ -411,7 +411,7 @@ module DiminishingReturns = {
                   | Reducer_T.IEvLambda(lambda) => Ok(lambda)
                   | _ =>
                     "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions. A member of the array wasn't a function"
-                    ->Reducer_ErrorValue.REOther
+                    ->SqError.Message.REOther
                     ->Error
                   }
                 }, innerlambdas)
@@ -433,7 +433,7 @@ module DiminishingReturns = {
               }
             | _ =>
               "Error in Danger.diminishingMarginalReturnsForTwoFunctions"
-              ->Reducer_ErrorValue.REOther
+              ->SqError.Message.REOther
               ->Error
             },
           (),
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Date.res b/packages/squiggle-lang/src/rescript/FR/FR_Date.res
index c9732980..0e4b828d 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Date.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Date.res
@@ -4,7 +4,7 @@ open FunctionRegistry_Helpers
 let makeFn = (
   name: string,
   inputs: array<frType>,
-  fn: array<Reducer_T.value> => result<Reducer_T.value, errorValue>,
+  fn: array<Reducer_T.value> => result<Reducer_T.value, errorMessage>,
 ) =>
   Function.make(
     ~name,
@@ -66,7 +66,7 @@ let library = [
     | [IEvNumber(year)] =>
       switch DateTime.Date.makeFromYear(year) {
       | Ok(t) => IEvDate(t)->Ok
-      | Error(e) => Reducer_ErrorValue.RETodo(e)->Error
+      | Error(e) => SqError.Message.RETodo(e)->Error
       }
     | _ => Error(impossibleError)
     }
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Dict.res b/packages/squiggle-lang/src/rescript/FR/FR_Dict.res
index 13bcfe33..f844ceac 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Dict.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Dict.res
@@ -17,7 +17,7 @@ module Internals = {
     ->E.A2.fmap(((key, value)) => Wrappers.evArray([IEvString(key), value]))
     ->Wrappers.evArray
 
-  let fromList = (items: array<Reducer_T.value>): result<Reducer_T.value, errorValue> =>
+  let fromList = (items: array<Reducer_T.value>): result<Reducer_T.value, errorMessage> =>
     items
     ->E.A2.fmap(item => {
       switch (item: Reducer_T.value) {
@@ -59,7 +59,6 @@ let library = [
     ],
     (),
   ),
-
   Function.make(
     ~name="mergeMany",
     ~nameSpace,
@@ -72,13 +71,17 @@ let library = [
         ~inputs=[FRTypeArray(FRTypeDict(FRTypeAny))],
         ~run=(inputs, _, _) => {
           switch inputs {
-            | [IEvArray(dicts)] => {
-              dicts->Belt.Array.map(dictValue => switch dictValue {
-                | IEvRecord(dict) => dict
-                | _ => impossibleError->Reducer_ErrorValue.toException
-              })->Internals.mergeMany->Ok
-            }
-            | _ => impossibleError->Error
+          | [IEvArray(dicts)] =>
+            dicts
+            ->Belt.Array.map(dictValue =>
+              switch dictValue {
+              | IEvRecord(dict) => dict
+              | _ => impossibleError->SqError.Message.toException
+              }
+            )
+            ->Internals.mergeMany
+            ->Ok
+          | _ => impossibleError->Error
           }
         },
         (),
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Dist.res b/packages/squiggle-lang/src/rescript/FR/FR_Dist.res
index 3a7504f2..270e2b4a 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Dist.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Dist.res
@@ -16,14 +16,13 @@ module DistributionCreation = {
       r
       ->E.R.bind(Process.DistOrNumberToDist.twoValuesUsingSymbolicDist(~fn, ~values=_, ~env))
       ->E.R2.fmap(Wrappers.evDistribution)
-      ->E.R2.errMap(e => Reducer_ErrorValue.REOther(e))
+      ->E.R2.errMap(e => SqError.Message.REOther(e))
 
     let make = (name, fn) => {
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeDistOrNumber, FRTypeDistOrNumber],
-        ~run=(inputs, env, _) =>
-          inputs->Prepare.ToValueTuple.twoDistOrNumber->process(~fn, ~env),
+        ~run=(inputs, env, _) => inputs->Prepare.ToValueTuple.twoDistOrNumber->process(~fn, ~env),
         (),
       )
     }
@@ -43,7 +42,9 @@ module DistributionCreation = {
         ~name,
         ~inputs=[FRTypeRecord([("mean", FRTypeDistOrNumber), ("stdev", FRTypeDistOrNumber)])],
         ~run=(inputs, env, _) =>
-          inputs->Prepare.ToValueTuple.Record.twoDistOrNumber(("mean", "stdev"))->process(~fn, ~env),
+          inputs
+          ->Prepare.ToValueTuple.Record.twoDistOrNumber(("mean", "stdev"))
+          ->process(~fn, ~env),
         (),
       )
     }
@@ -54,14 +55,13 @@ module DistributionCreation = {
       r
       ->E.R.bind(Process.DistOrNumberToDist.oneValueUsingSymbolicDist(~fn, ~value=_, ~env))
       ->E.R2.fmap(Wrappers.evDistribution)
-      ->E.R2.errMap(e => Reducer_ErrorValue.REOther(e))
+      ->E.R2.errMap(e => SqError.Message.REOther(e))
 
     let make = (name, fn) =>
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeDistOrNumber],
-        ~run=(inputs, env, _) =>
-          inputs->Prepare.ToValueTuple.oneDistOrNumber->process(~fn, ~env),
+        ~run=(inputs, env, _) => inputs->Prepare.ToValueTuple.oneDistOrNumber->process(~fn, ~env),
         (),
       )
   }
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_GenericDist.res b/packages/squiggle-lang/src/rescript/FR/FR_GenericDist.res
index 6f98d132..72249d19 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_GenericDist.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_GenericDist.res
@@ -296,7 +296,7 @@ module Old = {
 
   let genericOutputToReducerValue = (o: DistributionOperation.outputType): result<
     Reducer_T.value,
-    Reducer_ErrorValue.errorValue,
+    SqError.Message.t,
   > =>
     switch o {
     | Dist(d) => Ok(Reducer_T.IEvDistribution(d))
@@ -311,9 +311,9 @@ module Old = {
     switch dispatchToGenericOutput(call, environment) {
     | Some(o) => genericOutputToReducerValue(o)
     | None =>
-      Reducer_ErrorValue.REOther("Internal error in FR_GenericDist implementation")
-      ->Reducer_ErrorValue.ErrorException
-      ->raise
+      SqError.Message.REOther(
+        "Internal error in FR_GenericDist implementation",
+      )->SqError.Message.toException
     }
 }
 
@@ -405,6 +405,6 @@ let library = E.A.concatMany([
 let mxLambda = Reducer_Expression_Lambda.makeFFILambda((inputs, env, _) => {
   switch Old.dispatch(("mx", inputs), env) {
   | Ok(value) => value
-  | Error(e) => e->Reducer_ErrorValue.ErrorException->raise
+  | Error(e) => e->SqError.Message.toException
   }
 })
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Pointset.res b/packages/squiggle-lang/src/rescript/FR/FR_Pointset.res
index 4babe231..28684f34 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Pointset.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Pointset.res
@@ -7,31 +7,32 @@ let requiresNamespace = true
 let inputsToDist = (inputs: array<Reducer_T.value>, xyShapeToPointSetDist) => {
   // TODO - rewrite in more functional/functor-based style
   switch inputs {
-    | [IEvArray(items)] => {
-      items->Belt.Array.map(
-        item =>
-        switch item {
-          | IEvRecord(map) => {
-            let xValue = map->Belt.Map.String.get("x")
-            let yValue = map->Belt.Map.String.get("y")
-            switch (xValue, yValue) {
-            | (Some(IEvNumber(x)), Some(IEvNumber(y))) => (x, y)
-            | _ => impossibleError->Reducer_ErrorValue.toException
-            }
+  | [IEvArray(items)] =>
+    items
+    ->Belt.Array.map(item =>
+      switch item {
+      | IEvRecord(map) => {
+          let xValue = map->Belt.Map.String.get("x")
+          let yValue = map->Belt.Map.String.get("y")
+          switch (xValue, yValue) {
+          | (Some(IEvNumber(x)), Some(IEvNumber(y))) => (x, y)
+          | _ => impossibleError->SqError.Message.toException
           }
-          | _ => impossibleError->Reducer_ErrorValue.toException
         }
-      )->Ok->E.R.bind(r => r->XYShape.T.makeFromZipped->E.R2.errMap(XYShape.Error.toString))
-       ->E.R2.fmap(r => Reducer_T.IEvDistribution(PointSet(r->xyShapeToPointSetDist)))
-    }
-    | _ => impossibleError->Reducer_ErrorValue.toException
+      | _ => impossibleError->SqError.Message.toException
+      }
+    )
+    ->Ok
+    ->E.R.bind(r => r->XYShape.T.makeFromZipped->E.R2.errMap(XYShape.Error.toString))
+    ->E.R2.fmap(r => Reducer_T.IEvDistribution(PointSet(r->xyShapeToPointSetDist)))
+  | _ => impossibleError->SqError.Message.toException
   }
 }
 
 module Internal = {
   type t = PointSetDist.t
 
-  let toType = (r): result<Reducer_T.value, Reducer_ErrorValue.errorValue> =>
+  let toType = (r): result<Reducer_T.value, SqError.Message.t> =>
     switch r {
     | Ok(r) => Ok(Wrappers.evDistribution(PointSet(r)))
     | Error(err) => Error(REOperationError(err))
@@ -71,7 +72,7 @@ let library = [
             )
             ->E.R2.fmap(Wrappers.pointSet)
             ->E.R2.fmap(Wrappers.evDistribution)
-            ->E.R2.errMap(e => Reducer_ErrorValue.REDistributionError(e))
+            ->E.R2.errMap(e => SqError.Message.REDistributionError(e))
           | _ => Error(impossibleError)
           },
         (),
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Sampleset.res b/packages/squiggle-lang/src/rescript/FR/FR_Sampleset.res
index 5bbfb506..7f11ba7a 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Sampleset.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Sampleset.res
@@ -18,7 +18,7 @@ module Internal = {
     | _ => Error(Operation.SampleMapNeedsNtoNFunction)
     }
 
-  let toType = (r): result<Reducer_T.value, Reducer_ErrorValue.errorValue> =>
+  let toType = (r): result<Reducer_T.value, SqError.Message.t> =>
     switch r {
     | Ok(r) => Ok(Wrappers.evDistribution(SampleSet(r)))
     | Error(r) => Error(REDistributionError(SampleSetError(r)))
@@ -95,7 +95,7 @@ let libaryBase = [
             GenericDist.toSampleSetDist(dist, environment.sampleCount)
             ->E.R2.fmap(Wrappers.sampleSet)
             ->E.R2.fmap(Wrappers.evDistribution)
-            ->E.R2.errMap(e => Reducer_ErrorValue.REDistributionError(e))
+            ->E.R2.errMap(e => SqError.Message.REDistributionError(e))
           | _ => Error(impossibleError)
           },
         (),
@@ -115,9 +115,8 @@ let libaryBase = [
         ~inputs=[FRTypeArray(FRTypeNumber)],
         ~run=(inputs, _, _) => {
           let sampleSet =
-            inputs->Prepare.ToTypedArray.numbers |> E.R2.bind(r =>
-              SampleSetDist.make(r)->E.R2.errMap(_ => "AM I HERE? WHYERE AMI??")
-            )
+            inputs->Prepare.ToTypedArray.numbers
+              |> E.R2.bind(r => SampleSetDist.make(r)->E.R2.errMap(_ => "AM I HERE? WHYERE AMI??"))
           sampleSet
           ->E.R2.fmap(Wrappers.sampleSet)
           ->E.R2.fmap(Wrappers.evDistribution)
@@ -164,7 +163,7 @@ let libaryBase = [
           | [IEvLambda(lambda)] =>
             switch Internal.fromFn(lambda, environment, reducer) {
             | Ok(r) => Ok(r->Wrappers.sampleSet->Wrappers.evDistribution)
-            | Error(e) => e->Reducer_ErrorValue.REOperationError->Error
+            | Error(e) => e->SqError.Message.REOperationError->Error
             }
           | _ => Error(impossibleError)
           },
@@ -291,7 +290,7 @@ module Comparison = {
     r
     ->E.R2.fmap(r => r->Wrappers.sampleSet->Wrappers.evDistribution)
     ->E.R2.errMap(e =>
-      e->DistributionTypes.Error.sampleErrorToDistErr->Reducer_ErrorValue.REDistributionError
+      e->DistributionTypes.Error.sampleErrorToDistErr->SqError.Message.REDistributionError
     )
 
   let mkBig = (name, withDist, withFloat) =>
diff --git a/packages/squiggle-lang/src/rescript/FR/FR_Scoring.res b/packages/squiggle-lang/src/rescript/FR/FR_Scoring.res
index 63589e83..60cb82e5 100644
--- a/packages/squiggle-lang/src/rescript/FR/FR_Scoring.res
+++ b/packages/squiggle-lang/src/rescript/FR/FR_Scoring.res
@@ -6,7 +6,7 @@ let requiresNamespace = true
 let runScoring = (estimate, answer, prior, env) => {
   GenericDist.Score.logScore(~estimate, ~answer, ~prior, ~env)
   ->E.R2.fmap(FunctionRegistry_Helpers.Wrappers.evNumber)
-  ->E.R2.errMap(e => Reducer_ErrorValue.REDistributionError(e))
+  ->E.R2.errMap(e => SqError.Message.REDistributionError(e))
 }
 
 let library = [
@@ -31,14 +31,13 @@ let library = [
           ]),
         ],
         ~run=(inputs, environment, _) => {
-          switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.threeArgs(inputs, ("estimate", "answer", "prior")) {
+          switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.threeArgs(
+            inputs,
+            ("estimate", "answer", "prior"),
+          ) {
           | Ok([IEvDistribution(estimate), IEvDistribution(d), IEvDistribution(prior)]) =>
             runScoring(estimate, Score_Dist(d), Some(prior), environment)
-          | Ok([
-              IEvDistribution(estimate),
-              IEvNumber(d),
-              IEvDistribution(prior),
-            ]) =>
+          | Ok([IEvDistribution(estimate), IEvNumber(d), IEvDistribution(prior)]) =>
             runScoring(estimate, Score_Scalar(d), Some(prior), environment)
           | Error(e) => Error(e->FunctionRegistry_Helpers.wrapError)
           | _ => Error(FunctionRegistry_Helpers.impossibleError)
@@ -50,7 +49,10 @@ let library = [
         ~name="logScore",
         ~inputs=[FRTypeRecord([("estimate", FRTypeDist), ("answer", FRTypeDistOrNumber)])],
         ~run=(inputs, environment, _) => {
-          switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.twoArgs(inputs, ("estimate", "answer")) {
+          switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.twoArgs(
+            inputs,
+            ("estimate", "answer"),
+          ) {
           | Ok([IEvDistribution(estimate), IEvDistribution(d)]) =>
             runScoring(estimate, Score_Dist(d), None, environment)
           | Ok([IEvDistribution(estimate), IEvNumber(d)]) =>
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res
index 857044d7..93581b15 100644
--- a/packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res
+++ b/packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res
@@ -1,7 +1,7 @@
 @genType type reducerProject = ReducerProject_T.project //re-export
 
-type reducerError = ForTS_Reducer_ErrorValue.reducerError //use
-type reducerErrorValue = ForTS_Reducer_ErrorValue.reducerErrorValue //use
+type error = ForTS_SqError.error //use
+type errorMessage = ForTS_SqError.errorMessage //use
 
 type squiggleValue = ForTS_SquiggleValue.squiggleValue //use
 type squiggleValue_Record = ForTS_SquiggleValue.squiggleValue_Record //use
@@ -99,7 +99,7 @@ To set the includes one first has to call "parseIncludes". The parsed includes o
 @genType
 let getIncludes = (project: reducerProject, sourceId: string): result<
   array<string>,
-  reducerErrorValue,
+  errorMessage,
 > => project->Private.getIncludes(sourceId)
 
 /* Other sources contributing to the global namespace of this source. */
@@ -192,7 +192,7 @@ let getBindings = (project: reducerProject, sourceId: string): squiggleValue_Rec
 Get the result after running this source file or the project
 */
 @genType
-let getResult = (project: reducerProject, sourceId: string): result<squiggleValue, reducerError> =>
+let getResult = (project: reducerProject, sourceId: string): result<squiggleValue, error> =>
   project->Private.getResult(sourceId)
 
 /*
@@ -201,7 +201,7 @@ However, without a project, you cannot handle include directives.
 The source has to be include free
 */
 @genType
-let evaluate = (sourceCode: string): (result<squiggleValue, reducerError>, squiggleValue_Record) =>
+let evaluate = (sourceCode: string): (result<squiggleValue, error>, squiggleValue_Record) =>
   Private.evaluate(sourceCode)
 
 @genType
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS_Reducer_ErrorValue.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS_Reducer_ErrorValue.res
deleted file mode 100644
index 1392639b..00000000
--- a/packages/squiggle-lang/src/rescript/ForTS/ForTS_Reducer_ErrorValue.res
+++ /dev/null
@@ -1,21 +0,0 @@
-@genType type reducerError = Reducer_ErrorValue.error //alias
-@genType type reducerErrorValue = Reducer_ErrorValue.errorValue //alias
-@genType type location = Reducer_Peggy_Parse.location //alias
-
-@genType
-let toString = (e: reducerError): string => Reducer_ErrorValue.errorToString(e)
-
-@genType
-let getLocation = (e: reducerError): option<location> =>
-  switch e.stackTrace {
-  | Some(stack) => Some(stack.location)
-  | None => None
-  }
-
-@genType
-let createOtherError = (v: string): reducerError =>
-  Reducer_ErrorValue.REOther(v)->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue
-
-@genType
-let attachEmptyStackTraceToErrorValue = (v: reducerErrorValue): reducerError =>
-  Reducer_ErrorValue.attachEmptyStackTraceToErrorValue(v)
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS_SqError.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS_SqError.res
new file mode 100644
index 00000000..c6a4b131
--- /dev/null
+++ b/packages/squiggle-lang/src/rescript/ForTS/ForTS_SqError.res
@@ -0,0 +1,19 @@
+@genType type error = SqError.Error.t //alias
+@genType type errorMessage = SqError.Message.t //alias
+@genType type location = Reducer_Peggy_Parse.location //alias
+
+@genType
+let toString = (e: error): string => SqError.Error.toString(e)
+
+@genType
+let getLocation = (e: error): option<location> =>
+  switch e.stackTrace {
+  | Some(stack) => Some(stack.location)
+  | None => None
+  }
+
+@genType
+let createOtherError = (v: string): error => SqError.Message.REOther(v)->SqError.Error.fromMessage
+
+@genType
+let errorFromMessage = (v: errorMessage): error => v->SqError.Error.fromMessage
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS_SquiggleValue/ForTS_SquiggleValue.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS_SquiggleValue/ForTS_SquiggleValue.res
index ff029c95..2a8e8e1c 100644
--- a/packages/squiggle-lang/src/rescript/ForTS/ForTS_SquiggleValue/ForTS_SquiggleValue.res
+++ b/packages/squiggle-lang/src/rescript/ForTS/ForTS_SquiggleValue/ForTS_SquiggleValue.res
@@ -1,5 +1,5 @@
 @genType type squiggleValue = Reducer_T.value //re-export
-type reducerError = ForTS_Reducer_ErrorValue.reducerError //use
+type error = ForTS_SqError.error //use
 
 @genType type squiggleValue_Array = Reducer_T.arrayValue //re-export recursive type
 @genType type squiggleValue_Record = Reducer_T.map //re-export recursive type
@@ -69,7 +69,7 @@ let toString = (variant: squiggleValue) => Reducer_Value.toString(variant)
 // This is a useful method for unit tests.
 // Convert the result along with the error message to a string.
 @genType
-let toStringResult = (variantResult: result<squiggleValue, reducerError>) =>
+let toStringResult = (variantResult: result<squiggleValue, error>) =>
   Reducer_Value.toStringResult(variantResult)
 
 @genType
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res
index 949801c7..cd6562b9 100644
--- a/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res
+++ b/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res
@@ -1,5 +1,4 @@
-@genType type reducerErrorValue = ForTS_Reducer_ErrorValue.reducerErrorValue //re-export
-@genType type location = ForTS_Reducer_ErrorValue.location //re-export
+@genType type location = ForTS_SqError.location //re-export
 
 @genType type reducerProject = ForTS_ReducerProject.reducerProject //re-export
 @genType type squiggleValue = ForTS_SquiggleValue.squiggleValue //re-export
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
index e6929761..f39eecc4 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
@@ -1,5 +1,5 @@
 type internalExpressionValueType = Reducer_Value.internalExpressionValueType
-type errorValue = Reducer_ErrorValue.errorValue
+type errorMessage = SqError.Message.t
 
 /*
   Function Registry "Type". A type, without any other information.
@@ -32,7 +32,7 @@ type fnDefinition = {
     array<Reducer_T.value>,
     Reducer_T.environment,
     Reducer_T.reducerFn,
-  ) => result<Reducer_T.value, errorValue>,
+  ) => result<Reducer_T.value, errorMessage>,
 }
 
 type function = {
@@ -83,19 +83,17 @@ module FRType = {
     | (FRTypeNumeric, IEvNumber(_)) => true
     | (FRTypeNumeric, IEvDistribution(Symbolic(#Float(_)))) => true
     | (FRTypeLambda, IEvLambda(_)) => true
-    | (FRTypeArray(intendedType), IEvArray(elements)) => {
-        elements->Belt.Array.every(v => matchWithValue(intendedType, v))
-      }
+    | (FRTypeArray(intendedType), IEvArray(elements)) =>
+      elements->Belt.Array.every(v => matchWithValue(intendedType, v))
     | (FRTypeDict(r), IEvRecord(map)) =>
       map->Belt.Map.String.valuesToArray->Belt.Array.every(v => matchWithValue(r, v))
-    | (FRTypeRecord(recordParams), IEvRecord(map)) => {
+    | (FRTypeRecord(recordParams), IEvRecord(map)) =>
       recordParams->Belt.Array.every(((name, input)) => {
         switch map->Belt.Map.String.get(name) {
-          | Some(v) => matchWithValue(input, v)
-          | None => false
+        | Some(v) => matchWithValue(input, v)
+        | None => false
         }
       })
-    }
     | _ => false
     }
 
@@ -104,8 +102,7 @@ module FRType = {
     if !isSameLength {
       false
     } else {
-      E.A.zip(inputs, args)
-      ->Belt.Array.every(((input, arg)) => matchWithValue(input, arg))
+      E.A.zip(inputs, args)->Belt.Array.every(((input, arg)) => matchWithValue(input, arg))
     }
   }
 }
@@ -230,7 +227,7 @@ module Registry = {
     args: array<Reducer_T.value>,
     env: Reducer_T.environment,
     reducer: Reducer_T.reducerFn,
-  ): result<Reducer_T.value, errorValue> => {
+  ): result<Reducer_T.value, errorMessage> => {
     switch Belt.Map.String.get(registry.fnNameDict, fnName) {
     | Some(definitions) => {
         let showNameMatchDefinitions = () => {
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Helpers.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Helpers.res
index a5a0f523..9ace7e20 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Helpers.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Helpers.res
@@ -2,8 +2,8 @@ open FunctionRegistry_Core
 open Reducer_T
 
 let impossibleErrorString = "Wrong inputs / Logically impossible"
-let impossibleError: errorValue = impossibleErrorString->Reducer_ErrorValue.REOther
-let wrapError = e => Reducer_ErrorValue.REOther(e)
+let impossibleError: errorMessage = impossibleErrorString->SqError.Message.REOther
+let wrapError = e => SqError.Message.REOther(e)
 
 module Wrappers = {
   let symbolic = r => DistributionTypes.Symbolic(r)
@@ -30,21 +30,21 @@ module Prepare = {
       let twoArgs = (inputs: ts, (arg1: string, arg2: string)): result<ts, err> =>
         switch inputs {
         | [IEvRecord(map)] => {
-          let n1 = map->Belt.Map.String.getExn(arg1)
-          let n2 = map->Belt.Map.String.getExn(arg2)
-          Ok([n1, n2])
-        }
+            let n1 = map->Belt.Map.String.getExn(arg1)
+            let n2 = map->Belt.Map.String.getExn(arg2)
+            Ok([n1, n2])
+          }
         | _ => Error(impossibleErrorString)
         }
 
       let threeArgs = (inputs: ts, (arg1: string, arg2: string, arg3: string)): result<ts, err> =>
         switch inputs {
         | [IEvRecord(map)] => {
-          let n1 = map->Belt.Map.String.getExn(arg1)
-          let n2 = map->Belt.Map.String.getExn(arg2)
-          let n3 = map->Belt.Map.String.getExn(arg3)
-          Ok([n1, n2, n3])
-        }
+            let n1 = map->Belt.Map.String.getExn(arg1)
+            let n2 = map->Belt.Map.String.getExn(arg2)
+            let n3 = map->Belt.Map.String.getExn(arg3)
+            Ok([n1, n2, n3])
+          }
         | _ => Error(impossibleErrorString)
         }
     }
@@ -108,8 +108,10 @@ module Prepare = {
     }
 
     module Record = {
-      let twoDistOrNumber = (values: ts, labels: (string, string)): result<(frValueDistOrNumber, frValueDistOrNumber), err> =>
-        values->ToValueArray.Record.twoArgs(labels)->E.R.bind(twoDistOrNumber)
+      let twoDistOrNumber = (values: ts, labels: (string, string)): result<
+        (frValueDistOrNumber, frValueDistOrNumber),
+        err,
+      > => values->ToValueArray.Record.twoArgs(labels)->E.R.bind(twoDistOrNumber)
 
       let twoDist = (values: ts, labels: (string, string)): result<
         (DistributionTypes.genericDist, DistributionTypes.genericDist),
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_ChainPiece.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_ChainPiece.res
deleted file mode 100644
index e545bb2d..00000000
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_ChainPiece.res
+++ /dev/null
@@ -1,27 +0,0 @@
-// types are disabled until review and rewrite for 0.5 interpreter compatibility
-/*
-module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
-module T = Reducer_Dispatch_T
-module TypeChecker = Reducer_Type_TypeChecker
-open Reducer_Value
-
-type errorValue = Reducer_ErrorValue.errorValue
-
-let makeFromTypes = jumpTable => {
-  let dispatchChainPiece: T.dispatchChainPiece = (
-    (fnName, fnArgs): functionCall,
-    accessors: ProjectAccessorsT.t,
-  ) => {
-    let jumpTableEntry = jumpTable->Js.Array2.find(elem => {
-      let (candidName, candidType, _) = elem
-      candidName == fnName && TypeChecker.checkITypeArgumentsBool(candidType, fnArgs)
-    })
-    switch jumpTableEntry {
-    | Some((_, _, bridgeFn)) => bridgeFn(fnArgs, accessors)->Some
-    | _ => None
-    }
-  }
-  dispatchChainPiece
-}
-
-*/
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_T.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_T.res
deleted file mode 100644
index 0d852783..00000000
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_T.res
+++ /dev/null
@@ -1,21 +0,0 @@
-// module ExpressionT = Reducer_Expression_T
-// module ProjectAccessorsT = ReducerProject_ProjectAccessors_T
-
-// // Each piece of the dispatch chain computes the result or returns None so that the chain can continue
-// type dispatchChainPiece = (
-//   Reducer_Value.functionCall,
-//   ProjectAccessorsT.t,
-// ) => option<result<Reducer_T.value, Reducer_ErrorValue.errorValue>>
-
-// type dispatchChainPieceWithReducer = (
-//   Reducer_Value.functionCall,
-//   ProjectAccessorsT.t,
-//   Reducer_T.reducerFn,
-// ) => option<result<Reducer_T.value, Reducer_ErrorValue.errorValue>>
-
-// // This is a switch statement case implementation: get the arguments and compute the result
-// type genericIEvFunction = (
-//   array<Reducer_T.value>,
-//   ProjectAccessorsT.t,
-// ) => result<Reducer_T.value, Reducer_ErrorValue.errorValue>
-
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
deleted file mode 100644
index e2c1d495..00000000
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
+++ /dev/null
@@ -1,131 +0,0 @@
-type location = Reducer_Peggy_Parse.location
-
-@genType.opaque
-type errorValue =
-  | REArityError(option<string>, int, int)
-  | REArrayIndexNotFound(string, int)
-  | REAssignmentExpected
-  | REDistributionError(DistributionTypes.error)
-  | REExpectedType(string, string)
-  | REExpressionExpected
-  | REFunctionExpected(string)
-  | REFunctionNotFound(string)
-  | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
-  | REMacroNotFound(string)
-  | RENotAFunction(string)
-  | REOperationError(Operation.operationError)
-  | RERecordPropertyNotFound(string, string)
-  | RESymbolNotFound(string)
-  | RESyntaxError(string, option<location>)
-  | RETodo(string) // To do
-  | REUnitNotFound(string)
-  | RENeedToRun
-  | REOther(string)
-
-type t = errorValue
-
-exception ErrorException(errorValue)
-
-type rec stackTrace = {
-  location: location,
-  parent: option<stackTrace>,
-}
-
-@genType.opaque
-type error = {
-  error: t,
-  stackTrace: option<stackTrace>,
-}
-
-exception ExceptionWithStackTrace(error)
-
-let fromParseError = (
-  SyntaxError(message, location): Reducer_Peggy_Parse.parseError,
-) => RESyntaxError(message, location->Some)
-
-let errorValueToString = (err: errorValue) =>
-  switch err {
-  | REArityError(_oFnName, arity, usedArity) =>
-    `${Js.String.make(arity)} arguments expected. Instead ${Js.String.make(
-        usedArity,
-      )} argument(s) were passed.`
-  | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
-  | REAssignmentExpected => "Assignment expected"
-  | REExpressionExpected => "Expression expected"
-  | REFunctionExpected(msg) => `Function expected: ${msg}`
-  | REFunctionNotFound(msg) => `Function not found: ${msg}`
-  | REDistributionError(err) => `Distribution Math Error: ${DistributionTypes.Error.toString(err)}`
-  | REOperationError(err) => `Math Error: ${Operation.Error.toString(err)}`
-  | REJavaScriptExn(omsg, oname) => {
-      let answer = "JS Exception:"
-      let answer = switch oname {
-      | Some(name) => `${answer} ${name}`
-      | _ => answer
-      }
-      let answer = switch omsg {
-      | Some(msg) => `${answer}: ${msg}`
-      | _ => answer
-      }
-      answer
-    }
-  | REMacroNotFound(macro) => `Macro not found: ${macro}`
-  | RENotAFunction(valueString) => `${valueString} is not a function`
-  | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
-  | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
-  | RESyntaxError(desc, _) => `Syntax Error: ${desc}`
-  | RETodo(msg) => `TODO: ${msg}`
-  | REExpectedType(typeName, valueString) => `Expected type: ${typeName} but got: ${valueString}`
-  | REUnitNotFound(unitName) => `Unit not found: ${unitName}`
-  | 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 rec stackTraceToString = ({location, parent}: stackTrace) => {
-  `  Line ${location.start.line->Js.Int.toString}, column ${location.start.column->Js.Int.toString}, source ${location.source}\n` ++
-  switch parent {
-  | Some(parent) => stackTraceToString(parent)
-  | None => ""
-  }
-}
-
-let errorToString = (err: error) =>
-  switch err.stackTrace {
-  | Some(stack) => "Traceback:\n" ++ stack->stackTraceToString
-  | None => ""
-  } ++
-  err.error->errorValueToString
-
-let toException = (errorValue: t) => errorValue->ErrorException->raise
-
-let attachEmptyStackTraceToErrorValue = (errorValue: t) => {
-  error: errorValue,
-  stackTrace: None,
-}
-
-let attachLocationToErrorValue = (errorValue: t, location: location): error => {
-  error: errorValue,
-  stackTrace: Some({location: location, parent: None}),
-}
-
-let raiseNewExceptionWithStackTrace = (errorValue: t, location: location) =>
-  errorValue->attachLocationToErrorValue(location)->ExceptionWithStackTrace->raise
-
-let raiseExtendedExceptionWithStackTrace = ({error, stackTrace}: error, location: location) =>
-  {error: error, stackTrace: Some({location: location, parent: stackTrace})}
-  ->ExceptionWithStackTrace
-  ->raise
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 714daffe..d0060982 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
@@ -3,14 +3,12 @@ module Lambda = Reducer_Expression_Lambda
 module Result = Belt.Result
 module T = Reducer_T
 
-type errorValue = Reducer_ErrorValue.errorValue
-
-let toLocation = (expression: T.expression): Reducer_ErrorValue.location => {
+let toLocation = (expression: T.expression): SqError.location => {
   expression.ast.location
 }
 
-let throwFrom = (error: errorValue, expression: T.expression) =>
-  error->Reducer_ErrorValue.raiseNewExceptionWithStackTrace(expression->toLocation)
+let throwFrom = (error: SqError.Message.t, expression: T.expression) =>
+  error->SqError.Error.fromMessageWithLocation(expression->toLocation)->SqError.Error.throw
 
 /*
   Recursively evaluate the expression
@@ -110,11 +108,11 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
           let result = Lambda.doLambdaCall(lambda, argValues, context.environment, evaluate)
           (result, context)
         } catch {
-        | Reducer_ErrorValue.ErrorException(e) => e->throwFrom(expression) // function implementation returned an error without location
-        | Reducer_ErrorValue.ExceptionWithStackTrace(e) =>
-          Reducer_ErrorValue.raiseExtendedExceptionWithStackTrace(e, expression->toLocation) // function implementation probably called a lambda that threw an exception
-        | Js.Exn.Error(obj) =>
-          REJavaScriptExn(obj->Js.Exn.message, obj->Js.Exn.name)->throwFrom(expression)
+        | exn =>
+          exn
+          ->SqError.Error.fromException
+          ->SqError.Error.extend(expression->toLocation)
+          ->SqError.Error.throw
         }
       | _ => RENotAFunction(lambda->Reducer_Value.toString)->throwFrom(expression)
       }
@@ -128,24 +126,18 @@ module BackCompatible = {
   let parse = (peggyCode: string): result<T.expression, Reducer_Peggy_Parse.parseError> =>
     peggyCode->Reducer_Peggy_Parse.parse("main")->Result.map(Reducer_Peggy_ToExpression.fromNode)
 
-  let evaluate = (expression: T.expression): result<T.value, Reducer_ErrorValue.error> => {
+  let evaluate = (expression: T.expression): result<T.value, SqError.Error.t> => {
     let context = Reducer_Context.createDefaultContext()
     try {
       let (value, _) = expression->evaluate(context)
       value->Ok
     } catch {
-    | exn =>
-      exn
-      ->Reducer_ErrorValue.fromException
-      ->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue
-      ->Error // TODO - this could be done better (see ReducerProject)
+    | exn => exn->SqError.Error.fromException->Error
     }
   }
 
-  let evaluateString = (peggyCode: string): result<T.value, Reducer_ErrorValue.error> =>
+  let evaluateString = (peggyCode: string): result<T.value, SqError.Error.t> =>
     parse(peggyCode)
-    ->E.R2.errMap(e =>
-      e->Reducer_ErrorValue.fromParseError->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue
-    )
+    ->E.R2.errMap(e => e->SqError.Message.fromParseError->SqError.Error.fromMessage)
     ->Result.flatMap(evaluate)
 }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
index bd0a044a..965fc499 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression_ExpressionBuilder.res
@@ -1,7 +1,5 @@
-module BErrorValue = Reducer_ErrorValue
 module T = Reducer_T
 
-type errorValue = BErrorValue.errorValue
 type expression = Reducer_T.expression
 type expressionContent = Reducer_T.expressionContent
 
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 e9a85a1a..36e43b25 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
@@ -1,5 +1,3 @@
-module ErrorValue = Reducer_ErrorValue
-
 let doLambdaCall = (
   lambdaValue: Reducer_T.lambdaValue,
   args,
@@ -28,7 +26,7 @@ let makeLambda = (
     let argsLength = arguments->Js.Array2.length
     let parametersLength = parameters->Js.Array2.length
     if argsLength !== parametersLength {
-      ErrorValue.REArityError(None, parametersLength, argsLength)->ErrorValue.ErrorException->raise
+      SqError.Message.REArityError(None, parametersLength, argsLength)->SqError.Message.toException
     }
 
     let localBindings = bindings->Reducer_Bindings.extend
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res
index f7681ee7..ea0931f2 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res
@@ -1,7 +1,3 @@
-// deprecated, use Reducer_T instead
-// (value methods should be moved to Reducer_Value.res)
-
-module ErrorValue = Reducer_ErrorValue
 type environment = GenericDist.env
 module T = Reducer_T
 
@@ -76,13 +72,13 @@ let toStringFunctionCall = ((fn, args)): string => `${fn}(${argsToString(args)})
 let toStringResult = x =>
   switch x {
   | Ok(a) => `Ok(${toString(a)})`
-  | Error(m) => `Error(${ErrorValue.errorToString(m)})`
+  | Error(m) => `Error(${SqError.Error.toString(m)})`
   }
 
-let toStringResultOkless = (codeResult: result<t, ErrorValue.error>): string =>
+let toStringResultOkless = (codeResult: result<t, SqError.Error.t>): string =>
   switch codeResult {
   | Ok(a) => toString(a)
-  | Error(m) => `Error(${ErrorValue.errorToString(m)})`
+  | Error(m) => `Error(${SqError.Error.toString(m)})`
   }
 
 type internalExpressionValueType =
@@ -144,10 +140,10 @@ let functionCallSignatureToString = (functionCallSignature: functionCallSignatur
 
 let arrayToValueArray = (arr: array<t>): array<t> => arr
 
-let resultToValue = (rExpression: result<t, Reducer_ErrorValue.t>): t =>
+let resultToValue = (rExpression: result<t, SqError.Message.t>): t =>
   switch rExpression {
   | Ok(expression) => expression
-  | Error(errorValue) => Reducer_ErrorValue.toException(errorValue)
+  | Error(errorValue) => SqError.Message.toException(errorValue)
   }
 
 let recordToKeyValuePairs = (record: T.map): array<(string, t)> => record->Belt.Map.String.toArray
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
index 082b620c..8ead6e32 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
@@ -1,7 +1,6 @@
 // TODO: Auto clean project based on topology
 
 module Bindings = Reducer_Bindings
-module ErrorValue = Reducer_ErrorValue
 module ProjectItem = ReducerProject_ProjectItem
 module T = ReducerProject_T
 module Topology = ReducerProject_Topology
@@ -117,7 +116,7 @@ let getResultOption = (project: t, sourceId: string): ProjectItem.T.resultType =
 
 let getResult = (project: t, sourceId: string): ProjectItem.T.resultArgumentType =>
   switch getResultOption(project, sourceId) {
-  | None => RENeedToRun->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue->Error
+  | None => RENeedToRun->SqError.Error.fromMessage->Error
   | Some(result) => result
   }
 
@@ -171,7 +170,7 @@ let linkDependencies = (project: t, sourceId: string): Reducer_T.namespace => {
             "__result__",
             switch project->getResult(id) {
             | Ok(result) => result
-            | Error(error) => error->Reducer_ErrorValue.ExceptionWithStackTrace->raise
+            | Error(error) => error->SqError.Error.throw
             },
           ),
         ])
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ParseIncludes.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ParseIncludes.res
index 38370488..c0612be8 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ParseIncludes.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ParseIncludes.res
@@ -1,10 +1,7 @@
 @module("./ReducerProject_IncludeParser.js")
 external parse__: string => array<array<string>> = "parse"
 
-let parseIncludes = (expr: string): result<
-  array<(string, string)>,
-  Reducer_ErrorValue.errorValue,
-> =>
+let parseIncludes = (expr: string): result<array<(string, string)>, SqError.Message.t> =>
   try {
     let answer = parse__(expr)
     // let logEntry = answer->Js.Array2.joinWith(",")
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
index 567ff29b..07ecac88 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
@@ -155,7 +155,7 @@ let doRawParse = (this: t): T.rawParseArgumentType =>
   this
   ->getSource
   ->Reducer_Peggy_Parse.parse(this.sourceId)
-  ->E.R2.errMap(Reducer_ErrorValue.fromParseError)
+  ->E.R2.errMap(SqError.Message.fromParseError)
 
 let rawParse = (this: t): t =>
   this->getRawParse->E.O2.defaultFn(() => doRawParse(this))->setRawParse(this, _)
@@ -174,7 +174,7 @@ let buildExpression = (this: t): t => {
   }
 }
 
-let failRun = (this: t, e: Reducer_ErrorValue.error): t =>
+let failRun = (this: t, e: SqError.Error.t): t =>
   this->setResult(e->Error)->setContinuation(Reducer_Namespace.make())
 
 let doRun = (this: t, context: Reducer_T.context): t =>
@@ -188,24 +188,11 @@ let doRun = (this: t, context: Reducer_T.context): t =>
         ->setResult(result->Ok)
         ->setContinuation(contextAfterEvaluation.bindings->Reducer_Bindings.locals)
       } catch {
-      | Reducer_ErrorValue.ErrorException(e) =>
-        this->failRun(e->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue)
-      | Reducer_ErrorValue.ExceptionWithStackTrace(e) => this->failRun(e)
-      | _ =>
-        this->failRun(
-          RETodo(
-            "unhandled rescript exception",
-          )->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue,
-        )
+      | e => this->failRun(e->SqError.Error.fromException)
       }
-    | Error(e) => this->failRun(e->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue)
+    | Error(e) => this->failRun(e->SqError.Error.fromMessage)
     }
-  | None =>
-    this->failRun(
-      RETodo(
-        "attempt to run without expression",
-      )->Reducer_ErrorValue.attachEmptyStackTraceToErrorValue,
-    )
+  | None => this->failRun(RETodo("attempt to run without expression")->SqError.Error.fromMessage)
   }
 
 let run = (this: t, context: Reducer_T.context): t => {
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res
index 5d32a161..8ea3a814 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res
@@ -1,22 +1,21 @@
 module Parse = Reducer_Peggy_Parse
 module ExpressionT = Reducer_Expression_T
-open Reducer_ErrorValue
 
 type sourceArgumentType = string
 type sourceType = string
-type rawParseArgumentType = result<Parse.node, errorValue>
+type rawParseArgumentType = result<Parse.node, SqError.Message.t>
 type rawParseType = option<rawParseArgumentType>
-type expressionArgumentType = result<ExpressionT.t, errorValue>
+type expressionArgumentType = result<ExpressionT.t, SqError.Message.t>
 type expressionType = option<expressionArgumentType>
 type continuationArgumentType = Reducer_T.namespace
 type continuationType = option<continuationArgumentType>
-type continuationResultType = option<result<continuationArgumentType, errorValue>>
-type resultArgumentType = result<Reducer_T.value, error>
+type continuationResultType = option<result<continuationArgumentType, SqError.Message.t>>
+type resultArgumentType = result<Reducer_T.value, SqError.Error.t>
 type resultType = option<resultArgumentType>
 type continuesArgumentType = array<string>
 type continuesType = array<string>
 type includesArgumentType = string
-type includesType = result<array<string>, errorValue>
+type includesType = result<array<string>, SqError.Message.t>
 type importAsVariablesType = array<(string, string)>
 
 type projectItem = {
diff --git a/packages/squiggle-lang/src/rescript/SqError.res b/packages/squiggle-lang/src/rescript/SqError.res
new file mode 100644
index 00000000..15f72d54
--- /dev/null
+++ b/packages/squiggle-lang/src/rescript/SqError.res
@@ -0,0 +1,145 @@
+type location = Reducer_Peggy_Parse.location
+
+module Message = {
+  @genType.opaque
+  type t =
+    | REArityError(option<string>, int, int)
+    | REArrayIndexNotFound(string, int)
+    | REAssignmentExpected
+    | REDistributionError(DistributionTypes.error)
+    | REExpectedType(string, string)
+    | REExpressionExpected
+    | REFunctionExpected(string)
+    | REFunctionNotFound(string)
+    | REJavaScriptExn(option<string>, option<string>) // Javascript Exception
+    | REMacroNotFound(string)
+    | RENotAFunction(string)
+    | REOperationError(Operation.operationError)
+    | RERecordPropertyNotFound(string, string)
+    | RESymbolNotFound(string)
+    | RESyntaxError(string, option<location>)
+    | RETodo(string) // To do
+    | REUnitNotFound(string)
+    | RENeedToRun
+    | REOther(string)
+
+  exception MessageException(t)
+
+  let fromParseError = (
+    SyntaxError(message, location): Reducer_Peggy_Parse.parseError,
+  ) => RESyntaxError(message, location->Some)
+
+  let toString = (err: t) =>
+    switch err {
+    | REArityError(_oFnName, arity, usedArity) =>
+      `${Js.String.make(arity)} arguments expected. Instead ${Js.String.make(
+          usedArity,
+        )} argument(s) were passed.`
+    | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
+    | REAssignmentExpected => "Assignment expected"
+    | REExpressionExpected => "Expression expected"
+    | REFunctionExpected(msg) => `Function expected: ${msg}`
+    | REFunctionNotFound(msg) => `Function not found: ${msg}`
+    | REDistributionError(err) =>
+      `Distribution Math Error: ${DistributionTypes.Error.toString(err)}`
+    | REOperationError(err) => `Math Error: ${Operation.Error.toString(err)}`
+    | REJavaScriptExn(omsg, oname) => {
+        let answer = "JS Exception:"
+        let answer = switch oname {
+        | Some(name) => `${answer} ${name}`
+        | _ => answer
+        }
+        let answer = switch omsg {
+        | Some(msg) => `${answer}: ${msg}`
+        | _ => answer
+        }
+        answer
+      }
+    | REMacroNotFound(macro) => `Macro not found: ${macro}`
+    | RENotAFunction(valueString) => `${valueString} is not a function`
+    | RERecordPropertyNotFound(msg, index) => `${msg}: ${index}`
+    | RESymbolNotFound(symbolName) => `${symbolName} is not defined`
+    | RESyntaxError(desc, _) => `Syntax Error: ${desc}`
+    | RETodo(msg) => `TODO: ${msg}`
+    | REExpectedType(typeName, valueString) => `Expected type: ${typeName} but got: ${valueString}`
+    | REUnitNotFound(unitName) => `Unit not found: ${unitName}`
+    | RENeedToRun => "Need to run"
+    | REOther(msg) => `Error: ${msg}`
+    }
+
+  let fromException = exn =>
+    switch exn {
+    | MessageException(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) => errorValue->MessageException->raise
+}
+
+module StackTrace = {
+  type rec t = {
+    location: location,
+    parent: option<t>,
+  }
+
+  let rec toString = ({location, parent}: t) => {
+    `  Line ${location.start.line->Js.Int.toString}, column ${location.start.column->Js.Int.toString}, source ${location.source}\n` ++
+    switch parent {
+    | Some(parent) => toString(parent)
+    | None => ""
+    }
+  }
+}
+
+module Error = {
+  @genType.opaque
+  type t = {
+    message: Message.t,
+    stackTrace: option<StackTrace.t>,
+  }
+
+  exception SqException(t)
+
+  let toString = (err: t) => err.message->Message.toString
+
+  let toStringWithStackTrace = (err: t) =>
+    switch err.stackTrace {
+    | Some(stack) => "Traceback:\n" ++ stack->StackTrace.toString
+    | None => ""
+    } ++
+    err->toString
+
+  let fromMessage = (errorMessage: Message.t) => {
+    message: errorMessage,
+    stackTrace: None,
+  }
+
+  let fromMessageWithLocation = (errorMessage: Message.t, location: location): t => {
+    message: errorMessage,
+    stackTrace: Some({location: location, parent: None}),
+  }
+
+  let extend = ({message, stackTrace}: t, location: location) => {
+    message: message,
+    stackTrace: Some({location: location, parent: stackTrace}),
+  }
+
+  let throw = (t: t) => t->SqException->raise
+
+  let fromException = exn =>
+    switch exn {
+    | SqException(e) => e
+    | Message.MessageException(e) => e->fromMessage
+    | Js.Exn.Error(obj) => REJavaScriptExn(obj->Js.Exn.message, obj->Js.Exn.name)->fromMessage
+    | _ => REOther("Unknown exception")->fromMessage
+    }
+}
diff --git a/packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_StdLib.res b/packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_StdLib.res
index 3be93851..57311827 100644
--- a/packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_StdLib.res
+++ b/packages/squiggle-lang/src/rescript/SquiggleLibrary/SquiggleLibrary_StdLib.res
@@ -1,4 +1,4 @@
-exception ErrorException = Reducer_ErrorValue.ErrorException
+let throwMessage = SqError.Message.toException
 
 let stdLib: Reducer_T.namespace = {
   // constants
@@ -17,16 +17,15 @@ let stdLib: Reducer_T.namespace = {
 
           switch Belt.Array.get(aValueArray, index) {
           | Some(value) => value
-          | None => REArrayIndexNotFound("Array index not found", index)->ErrorException->raise
+          | None => REArrayIndexNotFound("Array index not found", index)->throwMessage
           }
         }
       | [IEvRecord(dict), IEvString(sIndex)] =>
         switch Belt.Map.String.get(dict, sIndex) {
         | Some(value) => value
-        | None =>
-          RERecordPropertyNotFound("Record property not found", sIndex)->ErrorException->raise
+        | None => RERecordPropertyNotFound("Record property not found", sIndex)->throwMessage
         }
-      | _ => REOther("Trying to access key on wrong value")->ErrorException->raise
+      | _ => REOther("Trying to access key on wrong value")->throwMessage
       }
     })->Reducer_T.IEvLambda,
   )
@@ -49,7 +48,7 @@ let stdLib: Reducer_T.namespace = {
         Reducer_Expression_Lambda.makeFFILambda((arguments, environment, reducer) => {
           switch FunctionRegistry_Library.call(name, arguments, environment, reducer) {
           | Ok(value) => value
-          | Error(error) => error->Reducer_ErrorValue.ErrorException->raise
+          | Error(error) => error->SqError.Message.toException
           }
         })->Reducer_T.IEvLambda,
       )