[Haskell-cafe] arr f

[Ross Paterson]

On Fri, Jan 27, 2006 at 08:20:07PM +0100, Sven Biedermann wrote:
> I have a problem with a function taken from class Arrow.
>  
>     arr :: (b -> c) -> a b c
>  
> To build my own arrow, i need to distinguish between different kinds
> of
> b or c.
> For instance, if b has the form (d,e), i want to construct something
> different as when having form (d,e,f).

If you want a different instance in each case, then you'll need a
different class: arr is polymorphic in b and c.  But perhaps there's
another way to do what you want.  Can you give more details?