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 4f4e1731..44b6abd2 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
@@ -23,6 +23,30 @@ let inputsTodist = (inputs: array<FunctionRegistry_Core.frValue>, makeDist) => {
   expressionValue
 }
 
+module Internal = {
+  type t = PointSetDist.t
+
+  let toType = (r): result<
+    ReducerInterface_InternalExpressionValue.t,
+    Reducer_ErrorValue.errorValue,
+  > =>
+    switch r {
+    | Ok(r) => Ok(Wrappers.evDistribution(PointSet(r)))
+    | Error(err) => Error(REOperationError(err))
+    }
+
+  let doLambdaCall = (aLambdaValue, list, environment, reducer) =>
+    switch Reducer_Expression_Lambda.doLambdaCall(aLambdaValue, list, environment, reducer) {
+    | Ok(IEvNumber(f)) => Ok(f)
+    | _ => Error(Operation.SampleMapNeedsNtoNFunction)
+    }
+
+  let mapY = (pointSetDist: t, aLambdaValue, env, reducer) => {
+    let fn = r => doLambdaCall(aLambdaValue, list{IEvNumber(r)}, env, reducer)
+    PointSetDist.T.mapYResult(~fn, pointSetDist)->toType
+  }
+}
+
 let library = [
   Function.make(
     ~name="fromDist",
@@ -53,6 +77,27 @@ let library = [
     ],
     (),
   ),
+  Function.make(
+    ~name="mapY",
+    ~nameSpace,
+    ~requiresNamespace=true,
+    ~examples=[`PointSet.mapY(mx(normal(5,2)), {|x| x + 1})`],
+    ~output=ReducerInterface_InternalExpressionValue.EvtDistribution,
+    ~definitions=[
+      FnDefinition.make(
+        ~name="mapY",
+        ~inputs=[FRTypeDist, FRTypeLambda],
+        ~run=(inputs, _, env, reducer) =>
+          switch inputs {
+          | [IEvDistribution(PointSet(dist)), IEvLambda(lambda)] =>
+            Internal.mapY(dist, lambda, env, reducer)->E.R2.errMap(Reducer_ErrorValue.errorToString)
+          | _ => Error(impossibleError)
+          },
+        (),
+      ),
+    ],
+    (),
+  ),
   Function.make(
     ~name="makeContinuous",
     ~nameSpace,
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 27b870ee..c40fe349 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Sampleset.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Sampleset.res
@@ -92,7 +92,7 @@ let library = [
             GenericDist.toSampleSetDist(dist, env.sampleCount)
             ->E.R2.fmap(Wrappers.sampleSet)
             ->E.R2.fmap(Wrappers.evDistribution)
-            ->E.R2.errMap(_ => "")
+            ->E.R2.errMap(DistributionTypes.Error.toString)
           | _ => Error(impossibleError)
           },
         (),
@@ -158,7 +158,7 @@ let library = [
           | [IEvLambda(lambda)] =>
             switch Internal.fromFn(lambda, env, reducer) {
             | Ok(r) => Ok(r->Wrappers.sampleSet->Wrappers.evDistribution)
-            | Error(_) => Error("issue")
+            | Error(e) => Error(Operation.Error.toString(e))
             }
           | _ => Error(impossibleError)
           },
@@ -180,7 +180,7 @@ let library = [
         ~run=(inputs, _, env, reducer) =>
           switch inputs {
           | [IEvDistribution(SampleSet(dist)), IEvLambda(lambda)] =>
-            Internal.map1(dist, lambda, env, reducer)->E.R2.errMap(_ => "")
+            Internal.map1(dist, lambda, env, reducer)->E.R2.errMap(Reducer_ErrorValue.errorToString)
           | _ => Error(impossibleError)
           },
         (),
@@ -207,7 +207,9 @@ let library = [
               IEvDistribution(SampleSet(dist2)),
               IEvLambda(lambda),
             ] =>
-            Internal.map2(dist1, dist2, lambda, env, reducer)->E.R2.errMap(_ => "")
+            Internal.map2(dist1, dist2, lambda, env, reducer)->E.R2.errMap(
+              Reducer_ErrorValue.errorToString,
+            )
           | _ => Error(impossibleError)
           }
         },
@@ -236,7 +238,9 @@ let library = [
               IEvDistribution(SampleSet(dist3)),
               IEvLambda(lambda),
             ] =>
-            Internal.map3(dist1, dist2, dist3, lambda, env, reducer)->E.R2.errMap(_ => "")
+            Internal.map3(dist1, dist2, dist3, lambda, env, reducer)->E.R2.errMap(
+              Reducer_ErrorValue.errorToString,
+            )
           | _ => Error(impossibleError)
           },
         (),
@@ -259,9 +263,9 @@ let library = [
         ~run=(inputs, _, env, reducer) =>
           switch inputs {
           | [IEvArray(dists), IEvLambda(lambda)] =>
-            Internal.mapN(dists, lambda, env, reducer)->E.R2.errMap(_e => {
-              "AHHH doesn't work"
-            })
+            Internal.mapN(dists, lambda, env, reducer)->E.R2.errMap(
+              Reducer_ErrorValue.errorToString,
+            )
           | _ => Error(impossibleError)
           },
         (),
diff --git a/packages/website/docs/Api/DistPointSet.md b/packages/website/docs/Api/DistPointSet.md
index 9c9c3d0d..bfd8ae82 100644
--- a/packages/website/docs/Api/DistPointSet.md
+++ b/packages/website/docs/Api/DistPointSet.md
@@ -46,3 +46,13 @@ PointSet.makeDiscrete([
   { x: 3, y: 0.1 },
 ]);
 ```
+
+### mapY
+
+```
+PointSet.mapY: (pointSetDist, (number => number)) => pointSetDist
+```
+
+```javascript
+normal(5,3) |> PointSet.fromDist |> PointSet.mapY({|x| x ^ 2}) |> normalize
+```