Ah. There are other approaches to this problem that result in compile-time errors for such programs. Maybe the TR guys will adopt one or figure out a better one! But for regular ole Racket, we're stuck with a runtime error, I'm afraid.
Robby On Sat, Apr 19, 2014 at 2:04 PM, Gustavo Massaccesi <gust...@oma.org.ar> wrote: >>> (letrec ([x (if #t 8 x)]) x) ;==>8 > > It was a mistake. I thought that the “x: undefined; ...” error was an > expansion-time error, not a run-time error. > > (I expected an error, because the x in the else part is “undefined”, > even if it’s never accessed.) > > Gustavo > > > On Sat, Apr 19, 2014 at 1:02 PM, Robby Findler > <ro...@eecs.northwestern.edu> wrote: >> These seem correct to me. What were you expecting (and why?). >> >> Robby >> >> >> On Saturday, April 19, 2014, Gustavo Massaccesi <gust...@oma.org.ar> wrote: >>> >>> I found another problem with the optimizer and the new undefined behavior. >>> >>> (letrec ([x (if #t 8 x)]) x) ;==>8 >>> >>> I also consider this correct in a strange sense :). >>> >>> Gustavo >>> >>> >>> Welcome to Racket v6.0.1.4. >>> > (letrec ([x x]) x) >>> x: undefined; >>> cannot use before initialization >>> context...: >>> C:\Program Files\Racket-6.0.1.4\collects\racket\private\misc.rkt:87:7 >>> > (letrec ([x 5]) x) >>> 5 >>> > (letrec ([x (if #t 8 x)]) x) >>> 8 >>> > (letrec ([x (if #f 8 x)]) x) >>> x: undefined; >>> cannot use before initialization >>> context...: >>> C:\Program Files\Racket-6.0.1.4\collects\racket\private\misc.rkt:87:7 >>> > >>> >>> >>> On Wed, Apr 16, 2014 at 10:09 AM, Matthias Felleisen >>> <matth...@ccs.neu.edu> wrote: >>> > >>> > Ah, too bad: >>> > >>> >> pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl >>> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> >> --- OLD/pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl >>> >> +++ NEW/pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl >>> >> @@ -3416,5 +3416,16 @@ >>> >> (read (open-input-bytes (get-output-bytes o)))))) >>> >> >>> >> ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; >>> >> +;; Check that an unsufe opertion's argument is >>> >> +;; not "optimized" away if it's a use of >>> >> +;; a variable before definition: >>> >> + >>> >> +(err/rt-test (let () >>> >> + (unsafe-fx+ x 1) >>> >> + (define x 3) >>> >> + x) >>> >> + exn:fail:contract:variable?) >>> >> + >>> >> +;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; >>> > >>> > >>> > :-) >>> > >>> > On Apr 16, 2014, at 9:02 AM, Matthias Felleisen <matth...@ccs.neu.edu> >>> > wrote: >>> > >>> >> >>> >> On Apr 15, 2014, at 9:29 PM, Asumu Takikawa <as...@ccs.neu.edu> wrote: >>> >> >>> >>> On 2014-04-15 18:13:31 -0400, claire alvis wrote: >>> >>>> The push below includes changes to letrec expressions, internal >>> >>>> definitions, units, classes, and certain ill-formed shared >>> >>>> expressions so >>> >>>> that they no longer leak the `undefined' value. >>> >>> >>> >>> This is great! (especially happy that TR, even with classes, doesn't >>> >>> have to worry about #<undefined> anymore) >>> >>> >>> >>> BTW, I found this weird behavior: >>> >>> >>> >>> Welcome to Racket v6.0.1.3. >>> >>> -> (require racket/unsafe/ops) >>> >>> -> (let () (+ x 3) (define x 3) 5) >>> >>> ; x: variable used before its definition [,bt for context] >>> >>> -> (let () (unsafe-fx+ x 3) (define x 3) 5) >>> >>> 5 >>> >> >>> >> >>> >> I consider this correct in a strange sense. >>> >> >>> >> Interestingly enough, >>> >> >>> >>> (let () (displayln (unsafe-fx+ x 3)) (define x 3) 5) >>> >> x: variable used before its definition >>> >> context...: >>> >> /Users/matthias/plt/racket/collects/racket/private/misc.rkt:87:7 >>> >> >>> >> which is good too. I don't know how Claire and Matthew did this, >>> >> but it's good :-) >>> >> _________________________ >>> >> Racket Developers list: >>> >> http://lists.racket-lang.org/dev >>> > >>> > _________________________ >>> > Racket Developers list: >>> > http://lists.racket-lang.org/dev >>> _________________________ >>> Racket Developers list: >>> http://lists.racket-lang.org/dev _________________________ Racket Developers list: http://lists.racket-lang.org/dev
