Am Sonntag, 27. August 2006 01:02 schrieb 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
Probably my sleep deprived memory erred and what couldn't read either form was ghc 6.4.1. Bash history confirms that this is definitely a possibility. And since it's far easier to believe that I erred in this respect than that the derived Read instance of one day could read what that from another day couldn't, I'm pretty sure that's what happened. Sorry. Another thing: Would it be a good idea to create derived Read instances that could parse both, "A `And` A" and "And A A" ? Since 6.4.2 parses the former and 6.2.2 parses the latter that should be possible, I believe (and both forms are accepted at the ghci prompt). Cheers, Daniel -- "In My Egotistical Opinion, most people's C programs should be indented six feet downward and covered with dirt." -- Blair P. Houghton _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe