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[Chicken-users] letrec expansion
From: |
Dan Muresan |
Subject: |
[Chicken-users] letrec expansion |
Date: |
Sun, 26 Nov 2006 15:42:39 +0200 |
Hi,
I've noticed that letrec seems to have a problematic expansion. I'm
not sure if this has been discussed before (I couldn't find any
matches):
csi> (macroexpand '(letrec ((x 1)) x))
(let ((g1312 (##core#undefined))) (begin (##core#set! g1312 (quote 1)) g1312))
This definition doesn't use temporaries -- as, for example, in the
standard R5RS syntax-rules definition of letrec,
http://www.schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.3
Without using temporaries, some call/cc + letrec combinations don't work:
(letrec ((x (call/cc list)) (y (call/cc list)))
(if (procedure? x) (x (pair? y)))
(if (procedure? y) (y (pair? x)))
(let ((xk (car x)) (yk (car y)))
(and (call/cc xk) (call/cc yk) (call/cc xk))))
csi produces #f, while SISC, Scheme48 and guile correctly output #t.
Thanks go to Al Petrofsky for describing the problem.
Dan Muresan
http://alumnus.caltech.edu/~muresan/
- [Chicken-users] letrec expansion,
Dan Muresan <=