diff --git a/packages/squiggle-lang/__tests__/GenericDist/GenericOperation__Test.res b/packages/squiggle-lang/__tests__/GenericDist/GenericOperation__Test.res
index 52ab6c19..1e5b5397 100644
--- a/packages/squiggle-lang/__tests__/GenericDist/GenericOperation__Test.res
+++ b/packages/squiggle-lang/__tests__/GenericDist/GenericOperation__Test.res
@@ -12,9 +12,10 @@ let normalDist20: GenericDist_Types.genericDist = #Symbolic(#Normal({mean: 20.0,
 let uniformDist: GenericDist_Types.genericDist = #Symbolic(#Uniform({low: 9.0, high: 10.0}))
 
 let {toFloat, toDist, toString, toError} = module(GenericDist_GenericOperation.Output)
-let {run, outputMap} = module(GenericDist_GenericOperation)
+let {run} = module(GenericDist_GenericOperation)
+let {fmap} = module(GenericDist_GenericOperation.Output)
 let run = run(params)
-let outputMap = outputMap(params)
+let outputMap = fmap(params)
 let toExt: option<'a> => 'a = E.O.toExt(
   "Should be impossible to reach (This error is in test file)",
 )
diff --git a/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.res b/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.res
index e744543e..9cc93949 100644
--- a/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.res
+++ b/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.res
@@ -9,57 +9,59 @@ type params = {
   xyPointLength: int,
 }
 
-type outputType = 
+type outputType =
   | Dist(GenericDist_Types.genericDist)
   | Float(float)
   | String(string)
   | GenDistError(GenericDist_Types.error)
 
-module Output = {
-  let toDist = (o: outputType) =>
-    switch o {
+/*
+We're going to add another function to this module later, so first define a
+local version, which is not exported.
+*/
+module OutputLocal = {
+  type t = outputType
+
+  let toError = (t: outputType) =>
+    switch t {
+    | GenDistError(d) => Some(d)
+    | _ => None
+    }
+
+  let toErrorOrUnreachable = (t: t): error => t->toError->E.O2.default((Unreachable: error))
+
+  let toDistR = (t: t): result<genericDist, error> =>
+    switch t {
+    | Dist(r) => Ok(r)
+    | e => Error(toErrorOrUnreachable(e))
+    }
+
+  let toDist = (t: t) =>
+    switch t {
     | Dist(d) => Some(d)
     | _ => None
     }
 
-  let toFloat = (o: outputType) =>
-    switch o {
+  let toFloat = (t: t) =>
+    switch t {
     | Float(d) => Some(d)
     | _ => None
     }
 
-  let toString = (o: outputType) =>
-    switch o {
+  let toString = (t: t) =>
+    switch t {
     | String(d) => Some(d)
     | _ => None
     }
 
-  let toError = (o: outputType) =>
-    switch o {
-    | GenDistError(d) => Some(d)
-    | _ => None
+  //This is used to catch errors in other switch statements.
+  let fromResult = (r: result<t, error>): outputType =>
+    switch r {
+    | Ok(t) => t
+    | Error(e) => GenDistError(e)
     }
 }
 
-let fromResult = (r: result<outputType, error>): outputType =>
-  switch r {
-  | Ok(o) => o
-  | Error(e) => GenDistError(e)
-  }
-
-//This is used to catch errors in other switch statements.
-let _errorMap = (o: outputType): error =>
-  switch o {
-  | GenDistError(r) => r
-  | _ => Unreachable
-  }
-
-let outputToDistResult = (o: outputType): result<genericDist, error> =>
-  switch o {
-  | Dist(r) => Ok(r)
-  | r => Error(_errorMap(r))
-  }
-
 let rec run = (extra, fnName: operation): outputType => {
   let {sampleCount, xyPointLength} = extra
 
@@ -70,14 +72,14 @@ let rec run = (extra, fnName: operation): outputType => {
   let toPointSetFn = r => {
     switch reCall(~fnName=#fromDist(#toDist(#toPointSet), r), ()) {
     | Dist(#PointSet(p)) => Ok(p)
-    | r => Error(_errorMap(r))
+    | e => Error(OutputLocal.toErrorOrUnreachable(e))
     }
   }
 
   let toSampleSetFn = r => {
     switch reCall(~fnName=#fromDist(#toDist(#toSampleSet(sampleCount)), r), ()) {
     | Dist(#SampleSet(p)) => Ok(p)
-    | r => Error(_errorMap(r))
+    | e => Error(OutputLocal.toErrorOrUnreachable(e))
     }
   }
 
@@ -85,20 +87,20 @@ let rec run = (extra, fnName: operation): outputType => {
     reCall(
       ~fnName=#fromDist(#toDistCombination(#Pointwise, #Multiply, #Float(weight)), r),
       (),
-    )->outputToDistResult
+    )->OutputLocal.toDistR
 
   let pointwiseAdd = (r1, r2) =>
     reCall(
       ~fnName=#fromDist(#toDistCombination(#Pointwise, #Add, #Dist(r2)), r1),
       (),
-    )->outputToDistResult
+    )->OutputLocal.toDistR
 
   let fromDistFn = (subFnName: GenericDist_Types.Operation.fromDist, dist: genericDist) =>
     switch subFnName {
     | #toFloat(fnName) =>
       GenericDist.operationToFloat(dist, ~toPointSetFn, ~operation=fnName)
       ->E.R2.fmap(r => Float(r))
-      ->fromResult
+      ->OutputLocal.fromResult
     | #toString => dist->GenericDist.toString->String
     | #toDist(#inspect) => {
         Js.log2("Console log requested: ", dist)
@@ -108,27 +110,30 @@ let rec run = (extra, fnName: operation): outputType => {
     | #toDist(#truncate(leftCutoff, rightCutoff)) =>
       GenericDist.truncate(~toPointSetFn, ~leftCutoff, ~rightCutoff, dist, ())
       ->E.R2.fmap(r => Dist(r))
-      ->fromResult
+      ->OutputLocal.fromResult
     | #toDist(#toPointSet) =>
-      dist->GenericDist.toPointSet(xyPointLength)->E.R2.fmap(r => Dist(#PointSet(r)))->fromResult
+      dist
+      ->GenericDist.toPointSet(xyPointLength)
+      ->E.R2.fmap(r => Dist(#PointSet(r)))
+      ->OutputLocal.fromResult
     | #toDist(#toSampleSet(n)) =>
-      dist->GenericDist.sampleN(n)->E.R2.fmap(r => Dist(#SampleSet(r)))->fromResult
+      dist->GenericDist.sampleN(n)->E.R2.fmap(r => Dist(#SampleSet(r)))->OutputLocal.fromResult
     | #toDistCombination(#Algebraic, _, #Float(_)) => GenDistError(NotYetImplemented)
     | #toDistCombination(#Algebraic, operation, #Dist(t2)) =>
       dist
       ->GenericDist.algebraicCombination(~toPointSetFn, ~toSampleSetFn, ~operation, ~t2)
       ->E.R2.fmap(r => Dist(r))
-      ->fromResult
+      ->OutputLocal.fromResult
     | #toDistCombination(#Pointwise, operation, #Dist(t2)) =>
       dist
       ->GenericDist.pointwiseCombination(~toPointSetFn, ~operation, ~t2)
       ->E.R2.fmap(r => Dist(r))
-      ->fromResult
+      ->OutputLocal.fromResult
     | #toDistCombination(#Pointwise, operation, #Float(float)) =>
       dist
       ->GenericDist.pointwiseCombinationFloat(~toPointSetFn, ~operation, ~float)
       ->E.R2.fmap(r => Dist(r))
-      ->fromResult
+      ->OutputLocal.fromResult
     }
 
   switch fnName {
@@ -139,24 +144,28 @@ let rec run = (extra, fnName: operation): outputType => {
     dists
     ->GenericDist.mixture(~scaleMultiplyFn=scaleMultiply, ~pointwiseAddFn=pointwiseAdd)
     ->E.R2.fmap(r => Dist(r))
-    ->fromResult
+    ->OutputLocal.fromResult
   }
 }
 
 let runFromDist = (extra, fnName, dist) => run(extra, #fromDist(fnName, dist))
 let runFromFloat = (extra, fnName, float) => run(extra, #fromFloat(fnName, float))
 
-let outputMap = (
-  extra,
-  input: outputType,
-  fn: GenericDist_Types.Operation.singleParamaterFunction,
-): outputType => {
-  let newFnCall: result<operation, error> = switch (fn, input) {
-  | (#fromDist(fromDist), Dist(o)) => Ok(#fromDist(fromDist, o))
-  | (#fromFloat(fromDist), Float(o)) => Ok(#fromFloat(fromDist, o))
-  | (_, GenDistError(r)) => Error(r)
-  | (#fromDist(_), _) => Error(Other("Expected dist, got something else"))
-  | (#fromFloat(_), _) => Error(Other("Expected float, got something else"))
+module Output = {
+  include OutputLocal
+
+  let fmap = (
+    extra,
+    input: outputType,
+    fn: GenericDist_Types.Operation.singleParamaterFunction,
+  ): outputType => {
+    let newFnCall: result<operation, error> = switch (fn, input) {
+    | (#fromDist(fromDist), Dist(o)) => Ok(#fromDist(fromDist, o))
+    | (#fromFloat(fromDist), Float(o)) => Ok(#fromFloat(fromDist, o))
+    | (_, GenDistError(r)) => Error(r)
+    | (#fromDist(_), _) => Error(Other("Expected dist, got something else"))
+    | (#fromFloat(_), _) => Error(Other("Expected float, got something else"))
+    }
+    newFnCall->E.R2.fmap(r => run(extra, r))->OutputLocal.fromResult
   }
-  newFnCall->E.R2.fmap(r => run(extra, r))->fromResult
 }
diff --git a/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.resi b/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.resi
index 22864ed3..2769a505 100644
--- a/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.resi
+++ b/packages/squiggle-lang/src/rescript/GenericDist/GenericDist_GenericOperation.resi
@@ -16,15 +16,13 @@ let runFromDist: (
   GenericDist_Types.genericDist,
 ) => outputType
 let runFromFloat: (params, GenericDist_Types.Operation.fromDist, float) => outputType
-let outputMap: (
-  params,
-  outputType,
-  GenericDist_Types.Operation.singleParamaterFunction,
-) => outputType
 
 module Output: {
-  let toDist: outputType => option<GenericDist_Types.genericDist>
-  let toFloat: outputType => option<float>
-  let toString: outputType => option<string>
-  let toError: outputType => option<GenericDist_Types.error>
-}
+  type t = outputType
+  let toDist: t => option<GenericDist_Types.genericDist>
+  let toDistR: t => result<GenericDist_Types.genericDist, GenericDist_Types.error>
+  let toFloat: t => option<float>
+  let toString: t => option<string>
+  let toError: t => option<GenericDist_Types.error>
+  let fmap: (params, t, GenericDist_Types.Operation.singleParamaterFunction) => t
+}
\ No newline at end of file
diff --git a/packages/squiggle-lang/src/rescript/utility/E.res b/packages/squiggle-lang/src/rescript/utility/E.res
index 121ecb91..9c6c2a73 100644
--- a/packages/squiggle-lang/src/rescript/utility/E.res
+++ b/packages/squiggle-lang/src/rescript/utility/E.res
@@ -98,6 +98,10 @@ module O = {
   let max = compare(\">")
 }
 
+module O2 = {
+  let default = (a,b) => O.default(b,a)
+}
+
 /* Functions */
 module F = {
   let apply = (a, e) => a |> e