diff --git a/eval.c b/eval.c
index 1787465..2668ca3 100644
--- a/eval.c
+++ b/eval.c
@@ -164,27 +164,26 @@ fnprogn(Object *env, Object *list)
 Object*
 fnblock(Object *env, Object *list)
 {
-	if(list->type != OCELL)
+	if(list->type != OCELL|| (list->car->type != OSYMBOL&&list->car->type != OIDENT))
 		error("Malformed block");
 	Object *tag = car(list);
 	Object *body = cdr(list);
-	Object *frame = curframe(env);
 	jmp_buf jmp;
-	Object *b = frame->block = newblock(gc, tag, curblock(env), body, &jmp);
-	Object *res = 0;
+	Object *b = newblock(gc, tag, curblock(env), body, &jmp);
+	Object *sp = env->sp;
+	sp->car->block = b;
+	Object *res = &Nil;
 
 	if(setjmp(jmp) == 1){
+		env->sp->block = b->up;
+		env->sp = sp;
 		res = env->retval;
-		env->retval = 0;
-		Object *p = curblock(env);
-		for(;p!=b; p=p->up)
-			assert(p->tag != &Top);
-		curframe(env)->block = p->up;
+		env->retval = &Nil;
 		return res;
 	}
 
 	res = progn(env, body);
-	frame->block = frame->block->up;
+	sp->car->block = b->up;
 	return res;
 }
 
diff --git a/gc.c b/gc.c
index 834260b..accc214 100644
--- a/gc.c
+++ b/gc.c
@@ -42,7 +42,6 @@ findobj(GC *gc, uintptr_t *stk)
 static Object*
 cloneobj(GC *dst, GC *src, Object *obj)
 {
-	if(obj==0)return 0;
 	if(obj->type==OBLTIN||obj->type==OSYMBOL) return obj;
 	if(obj->flag&FORWARD) return obj->forward;
 
@@ -133,7 +132,7 @@ gcraise(GC *src)
 static void
 mark(GC *gc, Object *obj)
 {
-	if(obj==0||obj->flag&USING||obj->type==ONONE||obj->type==OSYMBOL||obj->type==OBLTIN)
+	if(obj->flag&USING||obj->type==ONONE||obj->type==OSYMBOL||obj->type==OBLTIN)
 		return;
 
 	obj->flag = USING;
diff --git a/lib/lib.lisp b/lib/lib.lisp
index c958ee1..96d16d8 100644
--- a/lib/lib.lisp
+++ b/lib/lib.lisp
@@ -1,5 +1,5 @@
 (defmacro defun (name args body) 
-		`(define ,name (block ,name (lambda ,args ,body))))
+		`(define ,name (lambda ,args (block ,name ,body))))
 
 (defmacro cond (expr . rest)
 	(if (not expr)
@@ -28,5 +28,9 @@
 	`(if (not ,test)
 		(progn ,@rest)))
 
+(defmacro return (res)
+	(return-from nil `,res))
+
 (defun list (x . y) (cons x y))
 
+
diff --git a/obj.c b/obj.c
index 38a7dd0..9e4c12e 100644
--- a/obj.c
+++ b/obj.c
@@ -57,6 +57,7 @@ newenv(GC *gc, Object *frames, Object *bp, Object *sp)
 	env->frames = frames;
 	env->bp = bp;
 	env->sp = sp;
+	env->retval = &Nil;
 	return env;
 }
 
diff --git a/repl.c b/repl.c
index 1640ec9..38ca3f3 100644
--- a/repl.c
+++ b/repl.c
@@ -31,6 +31,16 @@ error(char *fmt, ...)
 	exit(1);
 }
 
+/* remove all frames except Top */
+static void
+clearenv(Object *env)
+{
+	env->bp->cdr = &Nil;
+	env->bp->car->block = &Top; 
+	env->sp = env->bp;
+	env->retval = &Nil;
+}
+
 static void
 repl(Object *env, FILE *f, char *pre)
 {
@@ -39,6 +49,7 @@ repl(Object *env, FILE *f, char *pre)
 	if(setjmp(err) == 1){
 		if(feof(f))
 			exit(1);
+		clearenv(env);
 		skipline(f);
 	}
 	while(1){