add letrec macro

piclib/built-in.scm

@@ -225,3 +225,10 @@
 	     (eq? '*values-tag* (car res)))
         (apply consumer (cdr res))
         (consumer res))))
+
+(define-macro (letrec bindings . body)
+  (let ((vars (map (lambda (v) `(,v #f)) (map car bindings)))
+	(initials (map (lambda (v) `(set! ,@v)) bindings)))
+    `(let (,@vars)
+       (begin ,@initials)
+       ,@body)))

t/letrec.scm

@@ -0,0 +1,17 @@
+(define (print obj)
+  (write obj)
+  (newline)
+  obj)
+
+(letrec ((my-odd? (lambda (n)
+		    (if (= n 0)
+			#t
+			(not (my-even? (- n 1))))))
+	 (my-even? (lambda (n)
+		     (if (= n 0)
+			 #t
+			 (not (my-odd? (- n 1)))))))
+  (print '(my-odd? 42))
+  (print (my-odd? 42))
+  (print '(my-even? 57))
+  (print (my-even? 57)))