[racket-dev] Weird bug in Typed Racket predicate for Float 0.0

Hmm, curiouser and curiouser. Using the latest nightly build from
http://pre.racket-lang.org/installers/, I get #f #t #t #f both on my home
machine and work machine, which run Windows 7 64-bit. Now I'm really curious
as to what's going on here!

On Fri, Sep 9, 2011 at 12:08 PM, Vincent St-Amour <stamourv at ccs.neu.edu>wrote:

> At Thu, 8 Sep 2011 20:43:02 -0400,
> Luke Vilnis wrote:
> > Running this produces:
> >
> > eq? 0.0 #f
> > eqv? 0.0 #t
> > Float? #t
> > Float-Or-Integer? #f
>
> With the latest from git on Debian 32 bit, I get `#t' for all four.
>
> What environment are you using?
>
> > The part of TR that generates the compound contracts for unions
> containing
> > Float  types is using eq? instead of eqv? for the 0.0 and -0.0 case
> (which
> > started in version 5.1.1), which explains why the predicate fails.
> Somehow,
> > in the repro above, a 0.0 is being produced that doesn't eq? with the
> > literal 0.0. I tried doing this with, say, (eq? 0.0 (- (+ 3.0 1.0)
> > 4.0)) or (eq?
> > (exact->inexact 0) 0.0), but those both evaluate to #t, so either the
> > compiler is doing some very clever constant folding here, or eq? is
> supposed
> > to do value equality for floats. I'm assuming the former, but especially
> for
> > the exact->inexact case that seems pretty darn clever. Anyhow, I was
> hoping
> > someone could confirm my suspicion that this bug was so hard to reproduce
> > because of crazy compiler magic (also, assuming this is right and it's
> > simply an eq? vs. eqv? issue, I've sent along a patch).
>
> The patch looks fine. I'll apply it.
>
> Thanks!
>
> Vincent
>
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