[Haskell-cafe] OverlappingInstances-extension-like for type families

[adam vogt]

Hi Leza,

You can make a closed type family (not associated with the class as you have):

type family ComplexSignalType e where
 ComplexSignalType [C e] = [C e]
 ComplexSignalType [e] = [C e]

But then you pretty much have to define all instances in the same
module. If you instead use functional dependencies (FDs):

class Complexable s cs | s -> cs
instance Complexable [e] [C e]
instance Complexable [C e] [C e]

you can put these instances in separate modules. But the disadvantage
is that you have to deal with more type variables.

Regards,
Adam

On Mon, Jul 21, 2014 at 5:29 PM, Leza Morais Lutonda
<leza.ml at fecrd.cujae.edu.cu> wrote:
>
> Hello haskell-café,
>
> I just started working with type families, and come with some difficulties.
> Now I have a class:
>
> class (...) ⇒ Complexable s where
>     type ComplexSignalType s
>     ...
>
> Is there a possibility to have this two instances (in any way)?
>
> instance (RealFloat e) ⇒ Complexable [e] where
>     type ComplexSignalType [e] = [ℂ e]
>
> instance (RealFloat e) ⇒ Complexable [ℂ e] where
>     type ComplexSignalType [ℂ e] = [ℂ e]
>
>
> Thanks.
> --
> Leza Morais Lutonda, Lemol-C
> http://lemol.github.io
>
>
>
> 50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964
> http://cujae.edu.cu
>
>
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