diff --git a/static/js/languages/microscript/v2/runner.coffee b/static/js/languages/microscript/v2/runner.coffee
index bb1081b..6d64b69 100644
--- a/static/js/languages/microscript/v2/runner.coffee
+++ b/static/js/languages/microscript/v2/runner.coffee
@@ -256,6 +256,7 @@ class @Thread
     @paused = false
     @terminated = false
     @next_calls = []
+    @call_cache = new Map()
     @interface =
       pause: ()=>@pause()
       resume: ()=>@resume()
@@ -272,11 +273,16 @@ class @Thread
       if f instanceof Routine
         @processor.load f
       else
-        parser = new Parser(f,"")
-        parser.parse()
-        program = parser.program
-        compiler = new Compiler(program)
-        @processor.load compiler.routine
+        cached = @call_cache.get(f)
+        if cached?
+          @processor.load cached
+        else
+          parser = new Parser(f,"")
+          parser.parse()
+          program = parser.program
+          compiler = new Compiler(program)
+          @call_cache.set f, compiler.routine
+          @processor.load compiler.routine
         if (f == "update()" or f == "serverUpdate()") and @runner.updateControls?
           @runner.updateControls()
       true
diff --git a/static/js/languages/microscript/v2/runner.js b/static/js/languages/microscript/v2/runner.js
index a4cde56..24662ed 100644
--- a/static/js/languages/microscript/v2/runner.js
+++ b/static/js/languages/microscript/v2/runner.js
@@ -314,6 +314,7 @@ this.Thread = class Thread {
     this.paused = false;
     this.terminated = false;
     this.next_calls = [];
+    this.call_cache = new Map();
     this.interface = {
       pause: () => {
         return this.pause();
@@ -335,17 +336,23 @@ this.Thread = class Thread {
   }
 
   loadNext() {
-    var compiler, f, parser, program;
+    var cached, compiler, f, parser, program;
     if (this.next_calls.length > 0) {
       f = this.next_calls.splice(0, 1)[0];
       if (f instanceof Routine) {
         this.processor.load(f);
       } else {
-        parser = new Parser(f, "");
-        parser.parse();
-        program = parser.program;
-        compiler = new Compiler(program);
-        this.processor.load(compiler.routine);
+        cached = this.call_cache.get(f);
+        if (cached != null) {
+          this.processor.load(cached);
+        } else {
+          parser = new Parser(f, "");
+          parser.parse();
+          program = parser.program;
+          compiler = new Compiler(program);
+          this.call_cache.set(f, compiler.routine);
+          this.processor.load(compiler.routine);
+        }
         if ((f === "update()" || f === "serverUpdate()") && (this.runner.updateControls != null)) {
           this.runner.updateControls();
         }