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