[Haskell-cafe] bounded ranges

[Sebastian Fischer]

On Jul 23, 2010, at 12:21 AM, Chad Scherrer wrote:

> bdRangeSize :: (Ix i, Bounded i) => i -> Int
> bdRangeSize _ = rangeSize (minBound, maxBound :: i)

Unlike intended, the `i` in the type annotation to `maxBound` is not  
the same as the `i` in the signature of `bdRangeSize`. You need to  
enable ScopedTypeVariables and explicitly quantify the type variable  
`i` in order to refer to it in the annotation of `maxBound`:

     {-# LANGUAGE ScopedTypeVariables #-}

     import Data.Ix

     bdRangeSize :: forall i . (Ix i, Bounded i) => i -> Int
     bdRangeSize _ = rangeSize (minBound, maxBound :: i)

Cheers,
Sebastian

-- 
Underestimating the novelty of the future is a time-honored tradition.
(D.G.)