Re: [Haskell-beginners] Re: Overlapping Instances

El lun, 25-10-2010 a las 22:00 +0200, John Smith escribió:

Thank you. Why does this code succeed for a, but stills fails on instance Show B? Do they not both invoke the same Show A?

No, a doesn't use the instance for Array Int Bool. The (1,3) get defaulted to Integers. The following code will complain, though:

{-# LANGUAGE TypeSynonymInstances, OverlappingInstances, IncoherentInstances #-}

import Data.Array

type A = Array Int Bool

data B = B A

instance Show A where show a = "foo"

a = show $ listArray (1::Int,3) $ repeat True