RE: [Haskell-cafe] type/class question: toString

From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Graham Fawcett

Is there a way to declare a 'toString' function, such that

toString x | <x is a String> = x toString x | = show x

Perhaps, in the type system, there's a way to declare a ToString class, and somehow "inherit" all instances of Show as ToString instances?

I'm assuming you're not fond of the way the print function handles Strings? With GHC you can do this:

{-# OPTIONS -fallow-overlapping-instances #-} {-# OPTIONS -fallow-undecidable-instances #-}

class Show a => MyShow a where show_ :: a -> String instance MyShow String where show_ s = s instance (Show a) => MyShow a where show_ s = show s

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