diff --git a/packages/components/src/components/SquiggleErrorAlert.tsx b/packages/components/src/components/SquiggleErrorAlert.tsx
index d03e237f..e9dd4245 100644
--- a/packages/components/src/components/SquiggleErrorAlert.tsx
+++ b/packages/components/src/components/SquiggleErrorAlert.tsx
@@ -1,4 +1,4 @@
-import { SqError } from "@quri/squiggle-lang";
+import { SqError, SqLocation } from "@quri/squiggle-lang";
 import React from "react";
 import { ErrorAlert } from "./Alert";
 
@@ -6,10 +6,34 @@ type Props = {
   error: SqError;
 };
 
+const StackTraceLocation: React.FC<{ location: SqLocation }> = ({
+  location,
+}) => {
+  return (
+    <div>
+      Line {location.start.line}, column {location.start.column}
+    </div>
+  );
+};
+
+const StackTrace: React.FC<Props> = ({ error }) => {
+  return (
+    <div>
+      {error.toLocationArray().map((location, i) => (
+        <StackTraceLocation location={location} key={i} />
+      ))}
+    </div>
+  );
+};
+
 export const SquiggleErrorAlert: React.FC<Props> = ({ error }) => {
   return (
     <ErrorAlert heading="Error">
-      <pre>{error.toString()}</pre>
+      <div>{error.toString()}</div>
+      <div className="mt-4">Traceback:</div>
+      <div className="ml-4">
+        <StackTrace error={error} />
+      </div>
     </ErrorAlert>
   );
 };
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 e30d3274..3e5abceb 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
@@ -22,7 +22,7 @@ let expectExpressionToBe = (expr, answer, ~v="_", ()) => {
   } else {
     let a2 =
       rExpr
-      ->E.R2.errMap(e => e->SqError.Message.fromParseError->SqError.Error.fromMessage)
+      ->E.R2.errMap(e => e->SqError.Message.fromParseError->SqError.fromMessage)
       ->Result.flatMap(expr => Expression.BackCompatible.evaluate(expr))
       ->Reducer_Value.toStringResultOkless
     (a1, a2)->expect->toEqual((answer, v))
diff --git a/packages/squiggle-lang/scripts/lib.mjs b/packages/squiggle-lang/scripts/lib.mjs
index 6f778769..5fc91873 100644
--- a/packages/squiggle-lang/scripts/lib.mjs
+++ b/packages/squiggle-lang/scripts/lib.mjs
@@ -36,6 +36,6 @@ export const run = (src, { output, sampleCount } = {}) => {
     "Time:",
     String(time),
     result.tag === "Error" ? red(result.tag) : green(result.tag),
-    result.tag === "Error" ? result.value.toString() : ""
+    result.tag === "Error" ? result.value.toStringWithStackTrace() : ""
   );
 };
diff --git a/packages/squiggle-lang/src/js/SqError.ts b/packages/squiggle-lang/src/js/SqError.ts
index ea21dc11..5025e671 100644
--- a/packages/squiggle-lang/src/js/SqError.ts
+++ b/packages/squiggle-lang/src/js/SqError.ts
@@ -1,13 +1,25 @@
-import * as RSError from "../rescript/ForTS/ForTS_SqError.gen";
+import * as RSError from "../rescript/SqError.gen";
+
+export type SqLocation = RSError.location;
 
 export class SqError {
-  constructor(private _value: RSError.error) {}
+  constructor(private _value: RSError.t) {}
 
   toString() {
     return RSError.toString(this._value);
   }
 
+  toStringWithStackTrace() {
+    return RSError.toStringWithStackTrace(this._value);
+  }
+
   static createOtherError(v: string) {
     return new SqError(RSError.createOtherError(v));
   }
+
+  toLocationArray() {
+    const stackTrace = RSError.getStackTrace(this._value);
+
+    return stackTrace ? RSError.StackTrace.toLocationArray(stackTrace) : [];
+  }
 }
diff --git a/packages/squiggle-lang/src/js/SqProject.ts b/packages/squiggle-lang/src/js/SqProject.ts
index 30d8b245..b00b8927 100644
--- a/packages/squiggle-lang/src/js/SqProject.ts
+++ b/packages/squiggle-lang/src/js/SqProject.ts
@@ -1,12 +1,11 @@
 import * as RSProject from "../rescript/ForTS/ForTS_ReducerProject.gen";
-import * as RSError from "../rescript/ForTS/ForTS_SqError.gen";
+import * as RSError from "../rescript/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) {}
@@ -51,7 +50,7 @@ export class SqProject {
     return resultMap2(
       RSProject.getIncludes(this._value, sourceId),
       (a) => a,
-      (v: RSError.errorMessage) => new SqError(errorFromMessage(v))
+      (v: RSError.Message_t) => new SqError(RSError.fromMessage(v))
     );
   }
 
@@ -105,7 +104,7 @@ export class SqProject {
             items: [],
           })
         ),
-      (v: RSError.error) => new SqError(v)
+      (v: RSError.t) => new SqError(v)
     );
   }
 
diff --git a/packages/squiggle-lang/src/js/index.ts b/packages/squiggle-lang/src/js/index.ts
index aac26bd5..82e12103 100644
--- a/packages/squiggle-lang/src/js/index.ts
+++ b/packages/squiggle-lang/src/js/index.ts
@@ -13,7 +13,7 @@ export {
   environment,
   defaultEnvironment,
 } from "../rescript/ForTS/ForTS_Distribution/ForTS_Distribution.gen";
-export { SqError } from "./SqError";
+export { SqError, SqLocation } from "./SqError";
 export { SqShape } from "./SqPointSetDist";
 
 export { resultMap } from "./types";
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS_ReducerProject.res
index 93581b15..ff2ea2ce 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 error = ForTS_SqError.error //use
-type errorMessage = ForTS_SqError.errorMessage //use
+type error = SqError.t //use
+type errorMessage = SqError.Message.t //use
 
 type squiggleValue = ForTS_SquiggleValue.squiggleValue //use
 type squiggleValue_Record = ForTS_SquiggleValue.squiggleValue_Record //use
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS_SqError.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS_SqError.res
deleted file mode 100644
index c6a4b131..00000000
--- a/packages/squiggle-lang/src/rescript/ForTS/ForTS_SqError.res
+++ /dev/null
@@ -1,19 +0,0 @@
-@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 2a8e8e1c..d116b74b 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 error = ForTS_SqError.error //use
+type error = SqError.t //use
 
 @genType type squiggleValue_Array = Reducer_T.arrayValue //re-export recursive type
 @genType type squiggleValue_Record = Reducer_T.map //re-export recursive type
diff --git a/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res b/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res
index cd6562b9..b2bb9d98 100644
--- a/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res
+++ b/packages/squiggle-lang/src/rescript/ForTS/ForTS__Types.res
@@ -1,5 +1,3 @@
-@genType type location = ForTS_SqError.location //re-export
-
 @genType type reducerProject = ForTS_ReducerProject.reducerProject //re-export
 @genType type squiggleValue = ForTS_SquiggleValue.squiggleValue //re-export
 @genType type squiggleValue_Array = ForTS_SquiggleValue_Array.squiggleValue_Array //re-export
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 d0060982..d33d7ba3 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
@@ -8,7 +8,7 @@ let toLocation = (expression: T.expression): SqError.location => {
 }
 
 let throwFrom = (error: SqError.Message.t, expression: T.expression) =>
-  error->SqError.Error.fromMessageWithLocation(expression->toLocation)->SqError.Error.throw
+  error->SqError.fromMessageWithLocation(expression->toLocation)->SqError.throw
 
 /*
   Recursively evaluate the expression
@@ -108,11 +108,7 @@ let rec evaluate: T.reducerFn = (expression, context): (T.value, T.context) => {
           let result = Lambda.doLambdaCall(lambda, argValues, context.environment, evaluate)
           (result, context)
         } catch {
-        | exn =>
-          exn
-          ->SqError.Error.fromException
-          ->SqError.Error.extend(expression->toLocation)
-          ->SqError.Error.throw
+        | exn => exn->SqError.fromException->SqError.extend(expression->toLocation)->SqError.throw
         }
       | _ => RENotAFunction(lambda->Reducer_Value.toString)->throwFrom(expression)
       }
@@ -126,18 +122,18 @@ 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, SqError.Error.t> => {
+  let evaluate = (expression: T.expression): result<T.value, SqError.t> => {
     let context = Reducer_Context.createDefaultContext()
     try {
       let (value, _) = expression->evaluate(context)
       value->Ok
     } catch {
-    | exn => exn->SqError.Error.fromException->Error
+    | exn => exn->SqError.fromException->Error
     }
   }
 
-  let evaluateString = (peggyCode: string): result<T.value, SqError.Error.t> =>
+  let evaluateString = (peggyCode: string): result<T.value, SqError.t> =>
     parse(peggyCode)
-    ->E.R2.errMap(e => e->SqError.Message.fromParseError->SqError.Error.fromMessage)
+    ->E.R2.errMap(e => e->SqError.Message.fromParseError->SqError.fromMessage)
     ->Result.flatMap(evaluate)
 }
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res
index 4a0a77da..b2b57bed 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Peggy/Reducer_Peggy_Parse.res
@@ -1,7 +1,5 @@
 module Extra = Reducer_Extra
 
-// Do not gentype this, use LocationRange from peggy types instead
-// TODO - rename locationPoint -> location, location -> locationRange to match peggy
 @genType
 type locationPoint = {
   line: int,
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res
index ea0931f2..7abecb92 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Value.res
@@ -72,13 +72,13 @@ let toStringFunctionCall = ((fn, args)): string => `${fn}(${argsToString(args)})
 let toStringResult = x =>
   switch x {
   | Ok(a) => `Ok(${toString(a)})`
-  | Error(m) => `Error(${SqError.Error.toString(m)})`
+  | Error(m) => `Error(${SqError.toString(m)})`
   }
 
-let toStringResultOkless = (codeResult: result<t, SqError.Error.t>): string =>
+let toStringResultOkless = (codeResult: result<t, SqError.t>): string =>
   switch codeResult {
   | Ok(a) => toString(a)
-  | Error(m) => `Error(${SqError.Error.toString(m)})`
+  | Error(m) => `Error(${SqError.toString(m)})`
   }
 
 type internalExpressionValueType =
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
index 8ead6e32..6655f062 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res
@@ -116,7 +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->SqError.Error.fromMessage->Error
+  | None => RENeedToRun->SqError.fromMessage->Error
   | Some(result) => result
   }
 
@@ -170,7 +170,7 @@ let linkDependencies = (project: t, sourceId: string): Reducer_T.namespace => {
             "__result__",
             switch project->getResult(id) {
             | Ok(result) => result
-            | Error(error) => error->SqError.Error.throw
+            | Error(error) => error->SqError.throw
             },
           ),
         ])
diff --git a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
index 07ecac88..2211f004 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem.res
@@ -174,7 +174,7 @@ let buildExpression = (this: t): t => {
   }
 }
 
-let failRun = (this: t, e: SqError.Error.t): t =>
+let failRun = (this: t, e: SqError.t): t =>
   this->setResult(e->Error)->setContinuation(Reducer_Namespace.make())
 
 let doRun = (this: t, context: Reducer_T.context): t =>
@@ -188,11 +188,11 @@ let doRun = (this: t, context: Reducer_T.context): t =>
         ->setResult(result->Ok)
         ->setContinuation(contextAfterEvaluation.bindings->Reducer_Bindings.locals)
       } catch {
-      | e => this->failRun(e->SqError.Error.fromException)
+      | e => this->failRun(e->SqError.fromException)
       }
-    | Error(e) => this->failRun(e->SqError.Error.fromMessage)
+    | Error(e) => this->failRun(e->SqError.fromMessage)
     }
-  | None => this->failRun(RETodo("attempt to run without expression")->SqError.Error.fromMessage)
+  | None => this->failRun(RETodo("attempt to run without expression")->SqError.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 8ea3a814..9ef83536 100644
--- a/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res
+++ b/packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectItem_T.res
@@ -10,7 +10,7 @@ type expressionType = option<expressionArgumentType>
 type continuationArgumentType = Reducer_T.namespace
 type continuationType = option<continuationArgumentType>
 type continuationResultType = option<result<continuationArgumentType, SqError.Message.t>>
-type resultArgumentType = result<Reducer_T.value, SqError.Error.t>
+type resultArgumentType = result<Reducer_T.value, SqError.t>
 type resultType = option<resultArgumentType>
 type continuesArgumentType = array<string>
 type continuesType = array<string>
diff --git a/packages/squiggle-lang/src/rescript/SqError.res b/packages/squiggle-lang/src/rescript/SqError.res
index 15f72d54..2d04fcaf 100644
--- a/packages/squiggle-lang/src/rescript/SqError.res
+++ b/packages/squiggle-lang/src/rescript/SqError.res
@@ -86,6 +86,7 @@ module Message = {
 }
 
 module StackTrace = {
+  @genType.opaque
   type rec t = {
     location: location,
     parent: option<t>,
@@ -98,48 +99,68 @@ module StackTrace = {
     | 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
+  let rec toLocationList = (t: t): list<location> => {
+    switch t.parent {
+    | Some(parent) => Belt.List.add(toLocationList(parent), t.location)
+    | None => list{t.location}
     }
+  }
+
+  @genType
+  let toLocationArray = (t: t): array<location> => t->toLocationList->Belt.List.toArray
 }
+
+@genType.opaque
+type t = {
+  message: Message.t,
+  stackTrace: option<StackTrace.t>,
+}
+
+exception SqException(t)
+
+@genType
+let fromMessage = (errorMessage: Message.t): 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}),
+}
+
+@genType
+let getLocation = (t: t): option<location> => t.stackTrace->E.O2.fmap(stack => stack.location)
+
+@genType
+let getStackTrace = (t: t): option<StackTrace.t> => t.stackTrace
+
+@genType
+let toString = (t: t): string => t.message->Message.toString
+
+@genType
+let createOtherError = (v: string): t => Message.REOther(v)->fromMessage
+
+@genType
+let toStringWithStackTrace = (t: t) =>
+  switch t.stackTrace {
+  | Some(stack) => "Traceback:\n" ++ stack->StackTrace.toString
+  | None => ""
+  } ++
+  t->toString
+
+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
+  }