Add Whalesong specific versions of letrec and letrec-values to avoid the undefined value

whalesong/lang/kernel.rkt

@@ -37,6 +37,27 @@
 (provide current-print-mode)
 
 
+;; Custom letrec and letrec-values in order to avoid running
+;; into the (in Racket) newly introduced undefined value.
+
+(provide letrec letrec-values)  
+(define-syntax (letrec stx)
+  (syntax-case stx ()
+    [(_ ([id expr] ...) body ...)
+     (syntax/loc stx
+       (let ([id '**undefined**] ...)
+         (set! id expr) ...
+         (let () body ...)))]))
+
+(define-syntax (letrec-values stx)
+  (syntax-case stx ()
+    [(_ ([(id ...) expr] ...) body ...)
+     (syntax/loc stx
+       (let ([id '**undefined**] ... ...)
+         (set!-values (id ...) expr) ...
+         (let () body ...)))]))
+
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Primitive function stubs