[Haskell-cafe] MPTC and type classes issue (polymorphic '+')

[Pepe Iborra]

The main problem is that you cannot assume Integral for the values 20  
and 40. Those have types (Num a=>a).
And without the Integral assumption, you cannot define your instance.  
So what I would do is to create a thin wrapper:

 >i = id :: Integer -> Integer

and write:

 > input2 = [ InputDecs [ inp "emaLength" TyNumber ((i 20) + (i 40)) ] ]

Sometimes the simplest solution is the best one


Cheers
pepe

On 07/04/2007, at 14:35, Joel Reymont wrote:

> Pepe,
>
> On Apr 7, 2007, at 1:31 PM, Pepe Iborra wrote:
>
>> > input2 = [ InputDecs [ inp "emaLength" TyNumber ((20::Integer) +  
>> (40::Integer)) ] ]
>
> Thank you for your suggestion! I'm trying to make my AST definition  
> as succinct as possible, though, so I would really love to have 20  
> + 40. The issue is confined to a single module used during testing.
>
> 	Thanks, Joel
>
> --
> http://wagerlabs.com/
>
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