diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
index d026765d..62bd54a1 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_ErrorValue.res
@@ -5,6 +5,8 @@ type errorValue =
   | RERecordPropertyNotFound(string, string)
   | RETodo(string) // To do
 
+type t = errorValue
+
 let showError = err =>
   switch err {
   | REArrayIndexNotFound(msg, index) => `${msg}: ${Js.String.make(index)}`
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 e1b0d079..bb2500ca 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
@@ -8,6 +8,7 @@ open Reducer_ErrorValue
 
 type expression = T.expression
 type expressionValue = ExpressionValue.expressionValue
+type t = expression
 
 /*
   Shows the Lisp Code as text lisp code
@@ -31,10 +32,10 @@ let showResult = codeResult =>
 /*
   Converts a MathJs code to Lisp Code
 */
-let parse_ = (expr: string, parser, converter): result<expression, errorValue> =>
+let parse_ = (expr: string, parser, converter): result<t, errorValue> =>
   expr->parser->Result.flatMap(node => converter(node))
 
-let parse = (mathJsCode: string): result<expression, errorValue> =>
+let parse = (mathJsCode: string): result<t, errorValue> =>
   mathJsCode->parse_(MathJs.Parse.parse, MathJs.ToExpression.fromNode)
 
 module MapString = Belt.Map.String
@@ -54,7 +55,7 @@ let reduceValueList = (valueList: list<expressionValue>): result<expressionValue
 /*
   Recursively evaluate/reduce the code tree
 */
-let rec reduceExpression = (expression: expression, bindings): result<expressionValue, 'e> =>
+let rec reduceExpression = (expression: t, bindings): result<expressionValue, 'e> =>
   switch expression {
   | T.EValue(value) => value->Ok
   | T.EList(list) => {
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.resi b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.resi
new file mode 100644
index 00000000..1d4c5281
--- /dev/null
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.resi
@@ -0,0 +1,33 @@
+module Result = Belt.Result
+module T = Reducer_Expression_T
+type expression = T.expression
+type expressionValue = ReducerInterface.ExpressionValue.expressionValue
+type t = expression
+let show: T.expression => Js.String.t
+let showResult: result<T.expression, 'a> => string
+let parse_: (
+  string,
+  string => Result.t<'a, Reducer_ErrorValue.t>,
+  'a => Result.t<expression, Reducer_ErrorValue.t>,
+) => result<expression, Reducer_ErrorValue.t>
+let parse: string => result<expression, Reducer_ErrorValue.t>
+module MapString = Belt.Map.String
+type bindings = MapString.t<unit>
+let defaultBindings: bindings
+let reduceValueList: list<expressionValue> => result<
+  expressionValue,
+  Reducer_ErrorValue.t,
+>
+let reduceExpression: (expression, 'a) => result<
+  expressionValue,
+  Reducer_ErrorValue.t,
+>
+let evalWBindingsExpression: (expression, 'a) => result<
+  expressionValue,
+  Reducer_ErrorValue.t,
+>
+let evalWBindings: (string, bindings) => Result.t<
+  expressionValue,
+  Reducer_ErrorValue.t,
+>
+let eval: string => Result.t<expressionValue, Reducer_ErrorValue.t>