[Haskell-cafe] Numeric literals

[Lennart Augustsson]

I think your best bet is -fno-implicit-prelude, and defining
fromInteger = id :: Integer->Integer.

On Fri, Mar 20, 2009 at 10:06 AM, Lauri Oksanen <lassoken at gmail.com> wrote:
> Hi,
>
> Is there some way to tell ghc, how to interpret  numeric literals? I
> would like it to interpret
> 1 as 1 :: Integer
> not
> 1 as fromInteger (1 :: Integer)
>
> I have been playing with the following (rather ugly) code.
>
> {-# OPTIONS
>  -XFunctionalDependencies
>  -XMultiParamTypeClasses
>  -XTypeSynonymInstances
> #-}
> module Test where
> import Prelude(Integer, Double)
> import qualified Prelude as P
> default(Integer, Double)
>
> type Z = Integer
> type R = Double
>
> class Plus a b c | a b -> c where
>    (+) :: a -> b -> c
>
> instance Plus Z Z Z where
>    j + k =  j P.+ k
> instance Plus R R R where
>    x + y = x P.+ y
>
> instance Plus R Z R where
>    x + j = x P.+ P.fromInteger j
> instance Plus Z R R where
>    j + x = P.fromInteger j P.+ x
>
> x = (1 :: Z) + (1.0 :: R)
> --y = 1 + 1.0
>
> The commented line can't be compiled (because of ambiguous types, I think).
>
> - Lauri
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