diff --git a/packages/mondo/mondo.mjs b/packages/mondo/mondo.mjs
index 0e8dc857..89236a3b 100644
--- a/packages/mondo/mondo.mjs
+++ b/packages/mondo/mondo.mjs
@@ -175,10 +175,10 @@ export class MondoParser {
     return children;
   }
   get_lambda(args, children) {
-    // (.fast 2) = (lambda (_) (fast _ 2))
+    // (.fast 2) = (fn (_) (fast _ 2))
     children = this.desugar(children);
     const body = children.length === 1 ? children[0] : { type: 'list', children };
-    return [{ type: 'plain', value: 'lambda' }, { type: 'list', children: args }, body];
+    return [{ type: 'plain', value: 'fn' }, { type: 'list', children: args }, body];
   }
   // returns location range of given ast (even if desugared)
   get_range(ast, range = [Infinity, 0]) {
@@ -322,7 +322,7 @@ export class MondoRunner {
     console.log(printAst(ast));
     return this.evaluate(ast);
   }
-  evaluate(ast, scope = []) {
+  evaluate(ast, scope = {}) {
     if (ast.type !== 'list') {
       // is leaf
       if (ast.type === 'number') {
@@ -333,7 +333,20 @@ export class MondoRunner {
       return this.evaluator(ast, scope);
     }
 
-    if (ast.children[0]?.value === 'lambda') {
+    if (ast.children[0]?.value === 'def') {
+      if (ast.children.length !== 3) {
+        throw new Error(`expected "def" to have 3 children, but got ${ast.children.length}`);
+      }
+      // (def myfn  (fn (_) (ply 2 _)))
+      //      ^name ^body
+      const name = ast.children[1].value;
+      const body = this.evaluate(ast.children[2], scope);
+      scope[name] = body;
+      return this.evaluator(ast, scope);
+    }
+    if (ast.children[0]?.value === 'fn') {
+      // (fn (_)   (ply 2 _)
+      //     ^args ^ body
       const [_, args, body] = ast.children;
       const argNames = args.children.map((child) => child.value);
       return (x) => {
diff --git a/packages/mondo/test/mondo.test.mjs b/packages/mondo/test/mondo.test.mjs
index 338a1fec..47e0e165 100644
--- a/packages/mondo/test/mondo.test.mjs
+++ b/packages/mondo/test/mondo.test.mjs
@@ -119,10 +119,10 @@ describe('mondo sugar', () => {
       '(speed .8 (s (square bd (* 2 hh) (crush 4 cp) (angle mt ht lt))))',
     ));
 
-  it('should desugar (.)', () => expect(desguar('(.)')).toEqual('(lambda (_) _)'));
-  it('should desugar lambda', () => expect(desguar('(.fast 2)')).toEqual('(lambda (_) (fast 2 _))'));
+  it('should desugar (.)', () => expect(desguar('(.)')).toEqual('(fn (_) _)'));
+  it('should desugar lambda', () => expect(desguar('(.fast 2)')).toEqual('(fn (_) (fast 2 _))'));
   it('should desugar lambda with pipe', () =>
-    expect(desguar('(.fast 2 .room 1)')).toEqual('(lambda (_) (room 1 (fast 2 _)))'));
+    expect(desguar('(.fast 2 .room 1)')).toEqual('(fn (_) (room 1 (fast 2 _)))'));
   /* const lambda = parser.parse('(lambda (_) (fast 2 _))');
   const target = { type: 'plain', value: 'xyz' };
   it('should desugar_lambda', () =>
diff --git a/packages/mondough/mondough.mjs b/packages/mondough/mondough.mjs
index d84ceb0c..543dcfeb 100644
--- a/packages/mondough/mondough.mjs
+++ b/packages/mondough/mondough.mjs
@@ -49,15 +49,19 @@ function evaluator(node, scope) {
   if (type === 'list') {
     const { children } = node;
     const [name, ...args] = children;
+    if (name.value === 'def') {
+      return silence;
+    }
     // name is expected to be a pattern of functions!
     const first = name.firstCycle(true)[0];
-    if (typeof first?.value !== 'function') {
-      throw new Error(`[mondough] "${first}" is not a function`);
+    const type = typeof first?.value;
+    if (type !== 'function') {
+      throw new Error(`[mondough] "${first}" is not a function, got ${type} ...`);
     }
     return name
       .fmap((fn) => {
         if (typeof fn !== 'function') {
-          throw new Error(`[mondough] "${fn}" is not a function`);
+          throw new Error(`[mondough] "${fn}" is not a function b`);
         }
         return fn(...args);
       })
@@ -80,7 +84,6 @@ function evaluator(node, scope) {
   if (node.loc) {
     pat = pat.withLoc(node.loc[0], node.loc[1]);
   }
-  pat.foo = true;
   return pat;
 }