diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
index e6183ba0..45492433 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_TestHelpers.res
@@ -9,3 +9,6 @@ let expectParseToBe = (expr: string, answer: string) =>
 
 let expectEvalToBe = (expr: string, answer: string) =>
   Reducer.evaluate(expr)->ExpressionValue.toStringResult->expect->toBe(answer)
+
+let expectEvalBindingsToBe = (expr: string, bindings: Reducer.externalBindings, answer: string) =>
+  Reducer.evaluateWBindings(expr, bindings)->ExpressionValue.toStringResult->expect->toBe(answer)
diff --git a/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res b/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
index bd9101a2..62c0358a 100644
--- a/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
+++ b/packages/squiggle-lang/__tests__/Reducer/Reducer_test.res
@@ -10,6 +10,9 @@ let testEvalToBe = (expr, answer) => test(expr, () => expectEvalToBe(expr, answe
 
 let testDescriptionEvalToBe = (desc, expr, answer) => test(desc, () => expectEvalToBe(expr, answer))
 
+let testEvalBindingsToBe = (expr, bindings, answer) =>
+  test(expr, () => expectEvalBindingsToBe(expr, bindings, answer))
+
 describe("reducer using mathjs parse", () => {
   // Test the MathJs parser compatibility
   // Those tests toString that there is a semantic mapping from MathJs to Expression
@@ -102,6 +105,21 @@ describe("eval", () => {
     testEvalToBe("1; 1", "Error(Assignment expected)")
     testEvalToBe("x=1; x=1", "Error(Expression expected)")
   })
+  describe("external bindings", () => {
+    testEvalBindingsToBe(
+      "y=1; x+1",
+      list{("x", ExpressionValue.EvNumber(1.))}->Js.Dict.fromList,
+      "Ok(2)",
+    )
+    testEvalBindingsToBe(
+      // This will go away when we have a proper parser
+      // x+1 is an expression not a block!
+      // Bindings are done for blocks only
+      "x+1",
+      list{("x", ExpressionValue.EvNumber(1.))}->Js.Dict.fromList,
+      "Error(JS Exception: Error: Undefined symbol x)",
+    )
+  })
 })
 
 describe("test exceptions", () => {
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer.res b/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
index 7e93f367..2e4ac32e 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer.res
@@ -6,5 +6,7 @@ module Js = Reducer_Js
 module MathJs = Reducer_MathJs
 
 type expressionValue = Reducer_Expression.expressionValue
+type externalBindings = Expression.externalBindings
 let evaluate = Expression.eval
+let evaluateWBindings = Expression.evalWBindings
 let parse = Expression.parse
diff --git a/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi b/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
index 6f6a55a8..c20fce48 100644
--- a/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
+++ b/packages/squiggle-lang/src/rescript/Reducer/Reducer.resi
@@ -7,7 +7,10 @@ module MathJs = Reducer_MathJs
 
 @genType
 type expressionValue = ReducerInterface_ExpressionValue.expressionValue
-
+@genType
+type externalBindings = Expression.externalBindings
 @genType
 let evaluate: string => result<expressionValue, Reducer_ErrorValue.errorValue>
+@genType
+let evaluateWBindings: (string, externalBindings) => result<expressionValue, Reducer_ErrorValue.errorValue>
 let parse: string => result<Expression.expression, ErrorValue.errorValue>
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 b2b90633..0bf8c201 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
@@ -110,17 +110,31 @@ let reduceExpression = (expression: t, bindings: T.bindings): result<expressionV
   )
 }
 
-let evalWBindingsExpression = (aExpression, bindings): result<expressionValue, 'e> =>
+let evalWBindingsExpression_ = (aExpression, bindings): result<expressionValue, 'e> =>
   reduceExpression(aExpression, bindings)
 
 /*
   Evaluates MathJs code via Reducer using bindings and answers the result
 */
-let evalWBindings = (codeText: string, bindings: T.bindings) => {
-  parse(codeText)->Result.flatMap(code => code->evalWBindingsExpression(bindings))
+let evalWBindings_ = (codeText: string, bindings: T.bindings) => {
+  parse(codeText)->Result.flatMap(code => code->evalWBindingsExpression_(bindings))
 }
 
 /*
   Evaluates MathJs code via Reducer and answers the result
 */
-let eval = (code: string) => evalWBindings(code, defaultBindings)
+let eval = (code: string) => evalWBindings_(code, defaultBindings)
+
+type externalBindings = Js.Dict.t<expressionValue>
+
+/*
+  Evaluates code with external bindings. External bindings are a record of expression values.
+*/
+let evalWBindings = (code: string, externalBindings: externalBindings) => {
+  let keys = Js.Dict.keys(externalBindings)
+  let bindings = keys->Belt.Array.reduce(defaultBindings, (acc, key) => {
+    let value = Js.Dict.unsafeGet(externalBindings, key)
+    acc->Belt.Map.String.set(key, T.EValue(value))
+  })
+  evalWBindings_(code, bindings)
+}