Thanks Matthew, Jos > -----Original Message----- > From: Matthew Flatt [mailto:mfl...@cs.utah.edu] > Sent: 19 September 2010 03:54 > To: Jos Koot > Cc: 'PLT-Scheme Mailing List' > Subject: Re: [racket] internal definitions in r6rs > > This is a bug in the R6RS binding for `define'. Your program > works as it should if you use > > (define a > (lambda () > (define (b) "who cares?") > (define c (b)) > c)) > > or > > (define (a) > (let () > (define (b) "who cares?") > (define c (b)) > c)) > > because the problem is specific to `define' with the function > shorthand. > > I've pushed a repair. > > At Sat, 18 Sep 2010 12:52:26 +0200, "Jos Koot" 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
_________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
