It has been a while but I believe the r6 formal model covers this point. Robby
On Saturday, September 18, 2010, Jos Koot <jos.k...@telefonica.net> wrote: > > > > > > Hi, > > Section 11.3 > of R6RS states: "An expanded <body> (see chapter 10) containing variable > definitions can always be converted into an equivalent letrec* expression." > The > semantics of letrec* includes "each <variable> is assigned in > left-to-right order". This I interpret as allowing an internal definition to > refer to the value of a previously defined variable. > However: > > #!r6rs > > (import > (rnrs base (6)) > (rnrs io > simple (6))) > > (define > (a) > (define (b) "who cares?") > (define c (b)) > c) > > (write > (a)) > > Produces: > > Welcome to > DrRacket, version > 5.0.1.5--2010-09-13(5b54caebb066920e2585244a5ee444a3f121c966/a) > [3m]. > Language: r6rs; memory limit: 2000 MB. > . . procedure application: > expected procedure, given: #<undefined> (no arguments) > > The code > expands as follows. The hot spots is marked with an arrow. > > (module > anonymous-module r6rs > (#%plain-module-begin > (#%require > r6rs/private/prelims) > (#%require (lib > "rnrs/base-6.rkt")) > (#%require (for-meta #f (lib > "rnrs/base-6.rkt"))) > (#%require (lib > "rnrs/io/simple-6.rkt")) > (#%require (for-meta #f (lib > "rnrs/io/simple-6.rkt"))) > (define-values > (a) > (#%plain-lambda > () > (let-values (((b) undefined) ((c) > undefined)) > (let-values ; > <====== prohibits reference to value of previously > defined var > (((newtemp) > (#%plain-lambda () (letrec-values () (let-values () '"who > cares?")))) > ((newtemp:19) (#%app b))) ; > <====== > (set! b > newtemp) > (set! c > newtemp:19) > (let-values:20 () (let-values:21 () c)))))) > (#%app write (#%app > a)))) > > Is this a bug or do I misunderstand > R6RS? > The > following works correct: > > #!r6rs > > (import > (rnrs base > (6)) > (rnrs io simple (6))) > > (define (a) > (letrec* > ((b (lambda () "who cares?")) > (c > (b))) > c)) > > (write (a)) > > Thanks, > Jos > > > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
