diff --git a/src/Interp/ExpressionInterp.js b/src/Interp/ExpressionInterp.js
index 7da78f8..526ac86 100644
--- a/src/Interp/ExpressionInterp.js
+++ b/src/Interp/ExpressionInterp.js
@@ -12,6 +12,8 @@ import {
   applyClosure,
 } from '../Closure';
 
+import Options from '../Options';
+
 import { interp as statementInterp } from './StatementInterp';
 
 const interp = (exp, env) => {
@@ -52,7 +54,7 @@ const interp = (exp, env) => {
       const closure = interp(callee, env);
       const vals = rawArgs.map((obj) => interp(obj, env));
 
-      return applyClosure(interp, closure, vals, env);
+      return applyClosure(interp, closure, vals, env, Options.isLexical);
     }
 
     case 'UnaryExpression': {
diff --git a/src/Interp/__tests__/ExpressionInterp-test.js b/src/Interp/__tests__/ExpressionInterp-test.js
index 3cc0a06..efe9964 100644
--- a/src/Interp/__tests__/ExpressionInterp-test.js
+++ b/src/Interp/__tests__/ExpressionInterp-test.js
@@ -1,8 +1,11 @@
 'use strict';
 
 jest.unmock('../../Parser')
-    .unmock('../ExpressionInterp').unmock('../StatementInterp')
-    .unmock('../../Environment').unmock('../../Closure');
+    .unmock('../ExpressionInterp')
+    .unmock('../StatementInterp')
+    .unmock('../../Environment')
+    .unmock('../../Closure')
+    .unmock('../../Options');
 
 const { interp } = require('../ExpressionInterp');
 const { parse } = require('../../Parser');
@@ -11,7 +14,8 @@ const {
   extendEnv,
 } = require('../../Environment');
 
-import { makeClosure } from '../../Closure';
+const { makeClosure } = require('../../Closure');
+const Options = require('../../Options').default;
 
 const parseAndgetExp = (code) => parse(code).body[0].expression;
 
@@ -205,6 +209,34 @@ describe('Interp', () => {
     })());
   });
 
+  it('should support dynamic scope', () => {
+    Options.isLexical = false;
+
+    expect(interpExp(`(() => {
+      const adder = (x) => (y) => x + y;
+      const x = 100;
+      const add3ButActuallyAdd100 = adder(3);
+      return add3ButActuallyAdd100(5);
+    })()`)).toBe(100 + 5);
+
+    expect(interpExp(`(() => {
+      const adder = (x) => (y) => x + y;
+      const x = 100;
+      const add3ButActuallyAdd100 = adder(3);
+      return add3ButActuallyAdd100(5);
+    })()`)).toBe(100 + 5);
+
+    expect(interpExp(`(() => {
+      const x = 100;
+      const y = 200;
+      const adder = (x) => (y) => x + y;
+      const add3 = adder(3);
+      return add3(39);
+    })()`)).toBe(100 + 39);
+
+    Options.isLexical = true;
+  });
+
 
   // it('IfStatement', () => {
   //   expect(interpExp(`(() => {
diff --git a/src/Options.js b/src/Options.js
new file mode 100644
index 0000000..5a311b7
--- /dev/null
+++ b/src/Options.js
@@ -0,0 +1,9 @@
+/*
+ * This guy allows us to toggle the lexical/dynamic behavior at runtime.
+ */
+
+const Options = {
+  isLexical: true,
+};
+
+export default Options;