Thanks. I do not often use rnrs, for I prefer racket. But sometimes people ask me r6rs or even r5rs code. I have decided to send them racket code and let them make the required mods themselvesw. Thanks, Jos
> -----Original Message----- > From: robby.find...@gmail.com > [mailto:robby.find...@gmail.com] On Behalf Of Robby Findler > Sent: 19 September 2010 01:03 > To: Jos Koot > Cc: PLT-Scheme Mailing List > Subject: Re: [racket] internal definitions in r6rs > > 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
