diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
index 25eb87b7..ea43561e 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
@@ -47,6 +47,7 @@ type fnDefinition = {
     array<internalExpressionValue>,
     array<frValue>,
     GenericDist.env,
+    Reducer_Expression_T.reducerFn,
   ) => result<internalExpressionValue, string>,
 }
 
@@ -342,10 +343,15 @@ module FnDefinition = {
     }
   }
 
-  let run = (t: t, args: array<internalExpressionValue>, env: GenericDist.env) => {
+  let run = (
+    t: t,
+    args: array<internalExpressionValue>,
+    env: GenericDist.env,
+    reducer: Reducer_Expression_T.reducerFn,
+  ) => {
     let argValues = FRType.matchWithExpressionValueArray(t.inputs, args)
     switch argValues {
-    | Some(values) => t.run(args, values, env)
+    | Some(values) => t.run(args, values, env, reducer)
     | None => Error("Incorrect Types")
     }
   }
@@ -452,6 +458,7 @@ module Registry = {
     ~fnName: string,
     ~args: array<internalExpressionValue>,
     ~env: GenericDist.env,
+    ~reducer: Reducer_Expression_T.reducerFn,
   ) => {
     let relevantFunctions = Js.Dict.get(registry.fnNameDict, fnName) |> E.O.default([])
     let modified = {functions: relevantFunctions, fnNameDict: registry.fnNameDict}
@@ -468,7 +475,8 @@ module Registry = {
     }
 
     switch Matcher.Registry.findMatches(modified, fnName, args) {
-    | Matcher.Match.FullMatch(match) => match->matchToDef->E.O2.fmap(FnDefinition.run(_, args, env))
+    | Matcher.Match.FullMatch(match) =>
+      match->matchToDef->E.O2.fmap(FnDefinition.run(_, args, env, reducer))
     | SameNameDifferentArguments(m) => Some(Error(showNameMatchDefinitions(m)))
     | _ => None
     }
@@ -478,8 +486,9 @@ module Registry = {
     registry,
     (fnName, args): ReducerInterface_InternalExpressionValue.functionCall,
     env,
+    reducer: Reducer_Expression_T.reducerFn,
   ) => {
-    _matchAndRun(~registry, ~fnName, ~args, ~env)->E.O2.fmap(
+    _matchAndRun(~registry, ~fnName, ~args, ~env, ~reducer)->E.O2.fmap(
       E.R2.errMap(_, s => Reducer_ErrorValue.RETodo(s)),
     )
   }
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dict.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dict.res
index 4a52f187..69ceb9c6 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dict.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dict.res
@@ -52,7 +52,7 @@ let library = [
       FnDefinition.make(
         ~name="merge",
         ~inputs=[FRTypeDict(FRTypeAny), FRTypeDict(FRTypeAny)],
-        ~run=(inputs, _, _) => {
+        ~run=(inputs, _, _, _) => {
           switch inputs {
           | [IEvRecord(d1), IEvRecord(d2)] => Internals.merge(d1, d2)->Ok
           | _ => Error(impossibleError)
@@ -74,7 +74,7 @@ let library = [
       FnDefinition.make(
         ~name="mergeMany",
         ~inputs=[FRTypeArray(FRTypeDict(FRTypeAny))],
-        ~run=(_, inputs, _) =>
+        ~run=(_, inputs, _, _) =>
           inputs
           ->Prepare.ToTypedArray.dicts
           ->E.R2.fmap(E.Dict.concatMany)
@@ -96,7 +96,7 @@ let library = [
       FnDefinition.make(
         ~name="keys",
         ~inputs=[FRTypeDict(FRTypeAny)],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvRecord(d1)] => Internals.keys(d1)->Ok
           | _ => Error(impossibleError)
@@ -116,7 +116,7 @@ let library = [
       FnDefinition.make(
         ~name="values",
         ~inputs=[FRTypeDict(FRTypeAny)],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvRecord(d1)] => Internals.values(d1)->Ok
           | _ => Error(impossibleError)
@@ -136,7 +136,7 @@ let library = [
       FnDefinition.make(
         ~name="toList",
         ~inputs=[FRTypeDict(FRTypeAny)],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvRecord(dict)] => dict->Internals.toList->Ok
           | _ => Error(impossibleError)
@@ -156,7 +156,7 @@ let library = [
       FnDefinition.make(
         ~name="fromList",
         ~inputs=[FRTypeArray(FRTypeArray(FRTypeAny))],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvArray(items)] => Internals.fromList(items)
           | _ => Error(impossibleError)
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dist.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dist.res
index 424983d8..9e10577b 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dist.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Dist.res
@@ -21,7 +21,8 @@ module DistributionCreation = {
       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),
         (),
       )
     }
@@ -30,7 +31,7 @@ module DistributionCreation = {
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeRecord([("p5", FRTypeDistOrNumber), ("p95", FRTypeDistOrNumber)])],
-        ~run=(_, inputs, env) =>
+        ~run=(_, inputs, env, _) =>
           inputs->Prepare.ToValueTuple.Record.twoDistOrNumber->process(~fn, ~env),
         (),
       )
@@ -40,7 +41,7 @@ module DistributionCreation = {
       FnDefinition.make(
         ~name,
         ~inputs=[FRTypeRecord([("mean", FRTypeDistOrNumber), ("stdev", FRTypeDistOrNumber)])],
-        ~run=(_, inputs, env) =>
+        ~run=(_, inputs, env, _) =>
           inputs->Prepare.ToValueTuple.Record.twoDistOrNumber->process(~fn, ~env),
         (),
       )
@@ -57,7 +58,8 @@ module DistributionCreation = {
       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/FunctionRegistry/Library/FR_Fn.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Fn.res
index 512d564a..ee2ef343 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Fn.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Fn.res
@@ -51,7 +51,7 @@ let library = [
       FnDefinition.make(
         ~name="declare",
         ~inputs=[Declaration.frType],
-        ~run=(_, inputs, _) => {
+        ~run=(_, inputs, _, _) => {
           inputs->getOrError(0)->E.R.bind(Declaration.fromExpressionValue)
         },
         (),
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res
index 25924232..a181fb33 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_List.res
@@ -37,7 +37,7 @@ let library = [
       FnDefinition.make(
         ~name="make",
         ~inputs=[FRTypeNumber, FRTypeAny],
-        ~run=(inputs, _, _) => {
+        ~run=(inputs, _, _, _) => {
           switch inputs {
           | [IEvNumber(number), value] => Internals.makeFromNumber(number, value)->Ok
           | _ => Error(impossibleError)
@@ -58,7 +58,7 @@ let library = [
       FnDefinition.make(
         ~name="upTo",
         ~inputs=[FRTypeNumber, FRTypeNumber],
-        ~run=(_, inputs, _) =>
+        ~run=(_, inputs, _, _) =>
           inputs
           ->Prepare.ToValueTuple.twoNumbers
           ->E.R2.fmap(((low, high)) => Internals.upTo(low, high)),
@@ -76,7 +76,7 @@ let library = [
       FnDefinition.make(
         ~name="first",
         ~inputs=[FRTypeArray(FRTypeAny)],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvArray(array)] => Internals.first(array)
           | _ => Error(impossibleError)
@@ -95,7 +95,7 @@ let library = [
       FnDefinition.make(
         ~name="last",
         ~inputs=[FRTypeArray(FRTypeAny)],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvArray(array)] => Internals.last(array)
           | _ => Error(impossibleError)
@@ -115,7 +115,7 @@ let library = [
       FnDefinition.make(
         ~name="reverse",
         ~inputs=[FRTypeArray(FRTypeAny)],
-        ~run=(inputs, _, _) =>
+        ~run=(inputs, _, _, _) =>
           switch inputs {
           | [IEvArray(array)] => Internals.reverse(array)->Ok
           | _ => Error(impossibleError)
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Number.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Number.res
index c7027f06..472ae60b 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Number.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Number.res
@@ -9,7 +9,7 @@ module NumberToNumber = {
     FnDefinition.make(
       ~name,
       ~inputs=[FRTypeNumber],
-      ~run=(_, inputs, _) => {
+      ~run=(_, inputs, _, _) => {
         inputs
         ->getOrError(0)
         ->E.R.bind(Prepare.oneNumber)
@@ -25,7 +25,7 @@ module ArrayNumberDist = {
     FnDefinition.make(
       ~name,
       ~inputs=[FRTypeArray(FRTypeNumber)],
-      ~run=(_, inputs, _) =>
+      ~run=(_, inputs, _, _) =>
         Prepare.ToTypedArray.numbers(inputs)
         ->E.R.bind(r => E.A.length(r) === 0 ? Error("List is empty") : Ok(r))
         ->E.R.bind(fn),
@@ -36,7 +36,7 @@ module ArrayNumberDist = {
     FnDefinition.make(
       ~name,
       ~inputs=[FRTypeArray(FRTypeAny)],
-      ~run=(_, inputs, _) =>
+      ~run=(_, inputs, _, _) =>
         Prepare.ToTypedArray.numbers(inputs)
         ->E.R.bind(r => E.A.length(r) === 0 ? Error("List is empty") : Ok(r))
         ->E.R.bind(fn),
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 dc4daead..2c41a475 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Pointset.res
@@ -41,7 +41,7 @@ let library = [
       FnDefinition.make(
         ~name="makeContinuous",
         ~inputs=[FRTypeArray(FRTypeRecord([("x", FRTypeNumeric), ("y", FRTypeNumeric)]))],
-        ~run=(_, inputs, _) => inputsTodist(inputs, r => Continuous(Continuous.make(r))),
+        ~run=(_, inputs, _, _) => inputsTodist(inputs, r => Continuous(Continuous.make(r))),
         (),
       ),
     ],
@@ -64,7 +64,7 @@ let library = [
       FnDefinition.make(
         ~name="makeDiscrete",
         ~inputs=[FRTypeArray(FRTypeRecord([("x", FRTypeNumeric), ("y", FRTypeNumeric)]))],
-        ~run=(_, inputs, _) => inputsTodist(inputs, r => Discrete(Discrete.make(r))),
+        ~run=(_, inputs, _, _) => inputsTodist(inputs, r => Discrete(Discrete.make(r))),
         (),
       ),
     ],
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Scoring.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Scoring.res
index d8d5ddd0..972501e9 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Scoring.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Scoring.res
@@ -30,7 +30,7 @@ let library = [
             ("prior", FRTypeDist),
           ]),
         ],
-        ~run=(_, inputs, env) => {
+        ~run=(_, inputs, env, _) => {
           switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.threeArgs(inputs) {
           | Ok([FRValueDist(estimate), FRValueDistOrNumber(FRValueDist(d)), FRValueDist(prior)]) =>
             runScoring(estimate, Score_Dist(d), Some(prior), env)
@@ -49,7 +49,7 @@ let library = [
       FnDefinition.make(
         ~name="logScore",
         ~inputs=[FRTypeRecord([("estimate", FRTypeDist), ("answer", FRTypeDistOrNumber)])],
-        ~run=(_, inputs, env) => {
+        ~run=(_, inputs, env, _) => {
           switch FunctionRegistry_Helpers.Prepare.ToValueArray.Record.twoArgs(inputs) {
           | Ok([FRValueDist(estimate), FRValueDistOrNumber(FRValueDist(d))]) =>
             runScoring(estimate, Score_Dist(d), None, env)
@@ -74,7 +74,7 @@ let library = [
       FnDefinition.make(
         ~name="klDivergence",
         ~inputs=[FRTypeDist, FRTypeDist],
-        ~run=(_, inputs, env) => {
+        ~run=(_, inputs, env, _) => {
           switch inputs {
           | [FRValueDist(estimate), FRValueDist(d)] =>
             runScoring(estimate, Score_Dist(d), None, env)
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalLibrary.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalLibrary.res
index d6a14dea..fc0a2821 100644
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalLibrary.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExternalLibrary.res
@@ -4,16 +4,18 @@ type internalExpressionValue = InternalExpressionValue.t
 /*
   Map external calls of Reducer
 */
-let dispatch = (call: InternalExpressionValue.functionCall, environment, reducer, chain): result<
-  internalExpressionValue,
-  'e,
-> => {
+let dispatch = (
+  call: InternalExpressionValue.functionCall,
+  environment,
+  reducer: Reducer_Expression_T.reducerFn,
+  chain,
+): result<internalExpressionValue, 'e> => {
   E.A.O.firstSomeFn([
     () => ReducerInterface_GenericDistribution.dispatch(call, environment),
     () => ReducerInterface_Date.dispatch(call, environment),
     () => ReducerInterface_Duration.dispatch(call, environment),
     () => ReducerInterface_Number.dispatch(call, environment),
-    () => FunctionRegistry_Library.dispatch(call, environment),
+    () => FunctionRegistry_Library.dispatch(call, environment, reducer),
   ])->E.O2.default(chain(call, environment, reducer))
 }