f''' = ([]::[()]) == ([]::[()]) (Very pretty.)
So why doesn't ghc have 'default' instances? -----Original Message----- From: Eugene Kirpichov [mailto:ekirpic...@gmail.com] Sent: Fri 29/05/2009 10:51 To: Paul Keir Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] [] == [][MESSAGE NOT SCANNED] 2009/5/29 Paul Keir <pk...@dcs.gla.ac.uk>: > Hi all, > > GHC is not happy with this: > > f = [] == [] This fails because GHC doesn't know which 'a' you mean, and can't choose an Eq instance. > > nor this: > > f' = ([]::(Eq a) => [a]) == ([]::(Eq a) => [a]) > This fails for the same reason. > but this is OK: > > f'' = ([]::[Integer]) == ([]::[Integer]) > > GHCI is comfortable with [] == [], so why not GHC? 'Just curious. Because GHCI has some 'default' instances, whereas GHC doesn't. This time, it probably chooses a=(). > > Cheers, > Paul > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Eugene Kirpichov Web IR developer, market.yandex.ru
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