[Haskell-cafe] Derived Read instance for types with infix constructors (ghc 6.4.1)

[Daniel Fischer]

Extremely odd,

today ghc 6.4.2 (also on linux) works for me, too:
Prelude InfixR> show (A `And` A)
"A `And` A"
Prelude InfixR> show (And A A)
"A `And` A"
Prelude InfixR> read (show (And A A)) :: T
A `And` A
Prelude InfixR> read "And A A" :: T
*** Exception: Prelude.read: no parse
Prelude InfixR> read "A `And` A" :: T
A `And` A

(and it can't read "And A A", which is what ghc 6.2.2 could read), yesterday 
it couldn't read either form.

What sort of hiccough could produce such behaviour?????????

Bewildered,
Daniel

Am Samstag, 26. August 2006 21:47 schrieb Ian Lynagh:
> On Sat, Aug 26, 2006 at 10:15:17PM +0300, Misha Aizatulin wrote:
> > Neil Mitchell wrote:
> > >> *Main> show $ A `And` A
> > >> "A And A"
> > >
> > > For me, using GHCi 6.4.2 + Windows, I get:
> > > "A `And` A"
> >
> >   I installed GHC 6.4.2 now (on Linux). It really does print "A `And`
> > A", but still doesn't read it. Would you agree that GHC doesn't conform
> > to the Haskell Report here? In fact it seems to produce a Read instance
> > with no valid input for it!
>
> ghci on 6.4.2 Linux works for me:
>
> *Main> show (A `And` A)
> "A `And` A"
> *Main> read (show (A `And` A)) :: T
> A `And` A
>
> (recent 6.5 also seems fine).
>
>
> Thanks
> Ian
>
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