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 44218a4b..39c3492e 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
@@ -25,7 +25,7 @@ let expectToExpressionToBe = (expr, answer, ~v="_", ()) => {
       ->Result.flatMap(expr =>
         Expression.reduceExpression(
           expr,
-          ReducerInterface_DefaultExternalBindings.defaultInternalBindings,
+          ReducerInterface_StdLib.internalStdLib,
           ExpressionValue.defaultEnvironment,
         )
       )
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
index 092ccc9f..2c7dfb21 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
@@ -29,6 +29,7 @@ let expectEvalError = (expr: string) =>
 
 let expectEvalBindingsToBe = (expr: string, bindings: Reducer.externalBindings, answer: string) =>
   Reducer.evaluateUsingOptions(expr, ~externalBindings=Some(bindings), ~environment=None)
+  ->Reducer_Helpers.rRemoveDefaults
   ->ExpressionValue.toStringResult
   ->expect
   ->toBe(answer)
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
index 36fe3cd6..dfedffc7 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
@@ -24,4 +24,4 @@ let foreignFunctionInterface = (
 
 let defaultEnvironment = ExpressionValue.defaultEnvironment
 
-let defaultExternalBindings = ReducerInterface_DefaultExternalBindings.defaultExternalBindings
+let defaultExternalBindings = ReducerInterface_StdLib.externalStdLib
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 066a68b2..6b4168c3 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
@@ -116,14 +116,20 @@ let evaluateUsingOptions = (
   ~externalBindings: option<ReducerInterface_ExpressionValue.externalBindings>,
   code: string,
 ): result<expressionValue, errorValue> => {
-  let anEnvironment = switch environment {
-  | Some(env) => env
-  | None => ReducerInterface_ExpressionValue.defaultEnvironment
-  }
+  let anEnvironment = Belt.Option.getWithDefault(
+    environment,
+    ReducerInterface_ExpressionValue.defaultEnvironment,
+  )
 
   let anExternalBindings = switch externalBindings {
-  | Some(bindings) => bindings
-  | None => ReducerInterface_DefaultExternalBindings.defaultExternalBindings
+  | Some(bindings) => {
+      let cloneLib = ReducerInterface_StdLib.externalStdLib->Reducer_Category_Bindings.cloneRecord
+      Js.Dict.entries(bindings)->Js.Array2.reduce((acc, (key, value)) => {
+        acc->Js.Dict.set(key, value)
+        acc
+      }, cloneLib)
+    }
+  | None => ReducerInterface_StdLib.externalStdLib
   }
 
   let bindings = anExternalBindings->Bindings.fromExternalBindings
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_DefaultExternalBindings.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_DefaultExternalBindings.res
deleted file mode 100644
index 2e8abee4..00000000
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_DefaultExternalBindings.res
+++ /dev/null
@@ -1,6 +0,0 @@
-module Bindings = Reducer_Category_Bindings
-
-let defaultInternalBindings = Bindings.emptyBindings->SquiggleLibrary_Math.makeBindings
-
-@genType
-let defaultExternalBindings = defaultInternalBindings->Bindings.toRecord
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_StdLib.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_StdLib.res
new file mode 100644
index 00000000..f341f9e2
--- /dev/null
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_StdLib.res
@@ -0,0 +1,6 @@
+module Bindings = Reducer_Category_Bindings
+
+let internalStdLib = Bindings.emptyBindings->SquiggleLibrary_Math.makeBindings
+
+@genType
+let externalStdLib = internalStdLib->Bindings.toRecord