4 Dec
2000
4 Dec
'00
6:16 a.m.
You can't do it in standard Haskell, but with ghc extensions you can achieve the same effect. For example, the following program
data Showable = forall a . Show a => Showable a instance Show Showable where show (Showable x) = show x example = map show [Showable 'a', Showable 5] main = print example
produces the output
["'a'","5"]
And it isn't just ghc that has this extension. Hugs98 and nhc98 also implement it with this syntax. Hbc has the extension too (local forall quantification), but uses a slightly different syntax, since its implementation pre-dates all the others. Regards, Malcolm