diff --git a/mes.c b/mes.c
index 777a55f9..121d76b1 100644
--- a/mes.c
+++ b/mes.c
@@ -165,6 +165,13 @@ set_cdr_x (scm *x, scm *e)
 {
   assert (x->type == PAIR);
   x->cdr = e;
+  return &scm_unspecified;
+}
+
+scm *
+set_x (scm *x, scm *e, scm *a)
+{
+  return set_cdr_x (assoc (x, a), e);
 }
 
 scm *
@@ -477,6 +484,7 @@ lookup (char *x, scm *a)
   if (!strcmp (x, scm_lambda.name)) return &scm_lambda;
   if (!strcmp (x, scm_label.name)) return &scm_label;
   if (!strcmp (x, scm_nil.name)) return &scm_nil;
+  if (!strcmp (x, scm_symbol_set_x.name)) return &scm_symbol_set_x;
 
 #if QUASIQUOTE
   if (*x == '`') return &scm_symbol_quasiquote;
diff --git a/scm.mes b/scm.mes
index e9ddef52..6a38ce36 100755
--- a/scm.mes
+++ b/scm.mes
@@ -75,3 +75,20 @@
         (#t
          (cond ((pair? else) (car else))
                (#t *unspecified*)))))
+
+(define (unspecified-bindings bindings params)
+  (cond ((null? bindings) params)
+        (#t (unspecified-bindings
+             (cdr bindings)
+             (append params (cons (cons (caar bindings) '(*unspecified*)) '()))))))
+
+(define (letrec-setters bindings setters)
+  (cond ((null? bindings) setters)
+        (#t (letrec-setters (cdr bindings)
+                            (append setters
+                                    (cons (cons 'set! (car bindings)) '()))))))
+
+(define-macro (letrec bindings . body)
+  (cons 'let (cons (unspecified-bindings bindings '())
+                    (append (letrec-setters bindings '())
+                            body)))  )
diff --git a/test.mes b/test.mes
index bf9dfacb..e231e268 100644
--- a/test.mes
+++ b/test.mes
@@ -144,4 +144,15 @@
 (display (if (= 1 2) 'true 'false))
 (newline)
 
+(display 'factorial4=)
+(display
+ (letrec ((factorial (lambda (n)
+                       ;; (display 'factorial:)
+                       ;; (display n)
+                       ;; (newline)
+                       (if (= n 1) 1
+                           (* n (factorial (- n 1)))))))
+   (factorial 4)))
+(newline)
+
 '()