diff --git a/whalesong/js-assembler/assemble.rkt b/whalesong/js-assembler/assemble.rkt
index fc28d88..f410d12 100644
--- a/whalesong/js-assembler/assemble.rkt
+++ b/whalesong/js-assembler/assemble.rkt
@@ -31,11 +31,11 @@
 
 
 
-(: assemble/write-invoke ((Listof Statement) Boolean Output-Port -> Void))
+(: assemble/write-invoke ((Listof Statement) Output-Port (U 'no-trampoline 'without-preemption 'with-preemption) -> Void))
 ;; Writes out the JavaScript code that represents the anonymous invocation expression.
 ;; What's emitted is a function expression that, when invoked, runs the
 ;; statements.
-(define (assemble/write-invoke stmts without-trampoline? op)
+(define (assemble/write-invoke stmts op trampoline-option)
   (parameterize ([current-interned-symbol-table ((inst make-hash Symbol Symbol))]
                  [current-interned-constant-closure-table ((inst make-hash Symbol MakeCompiledProcedure))])
     (display "(function(M, success, fail, params) {\n" op)
@@ -73,14 +73,18 @@ for (param in params) {
 }
 EOF
               op)
-    (cond [without-trampoline?
+    (cond [(eq? trampoline-option 'no-trampoline)
            ;; If it's a module statement, we just want to call it directly, to get things loaded.
            (fprintf op "~a(M); })"
                     (assemble-label (make-Label (BasicBlock-name (first basic-blocks)))))]
           [else
            ;; Otherwise, we want to run under a trampolining context.
-           (fprintf op "M.trampoline(~a, true); })"
-                    (assemble-label (make-Label (BasicBlock-name (first basic-blocks)))))])))
+           (fprintf op "M.trampoline(~a, ~a); })"
+                    (assemble-label (make-Label (BasicBlock-name (first basic-blocks))))
+                    (cond [(eq? trampoline-option 'with-preemption)
+                           "false"]
+                          [(eq? trampoline-option 'without-preemption)
+                           "true"]))])))
 
 
 
diff --git a/whalesong/repl-prototype/server.rkt b/whalesong/repl-prototype/server.rkt
index 53634d8..492a79a 100644
--- a/whalesong/repl-prototype/server.rkt
+++ b/whalesong/repl-prototype/server.rkt
@@ -76,7 +76,7 @@
                     (define compiled-bytecode (compile-for-repl whalesong-bytecode))
                     (pretty-print compiled-bytecode)
                     (define assembled-op (open-output-string))
-                    (define assembled (assemble/write-invoke compiled-bytecode #f assembled-op))
+                    (define assembled (assemble/write-invoke compiled-bytecode assembled-op 'with-preemption))
                     (cons (get-output-string assembled-op) (loop))])))
          (printf "assembled codes ~a\n" assembled-codes)
          (write-json (hash 'compiledCodes assembled-codes)