[Haskell-cafe] Re: All equations must have the same arity - why?

[Achim Schneider]

"Neil Mitchell" <ndmitchell at gmail.com> wrote:

> Hi,
> 
> It's nice to write functions in point free style:
> 
> f = sort . nub
> 
> But sometimes I have to add an extra case, on a certain value:
> 
> f [] = [1]
> f = sort . nub
> 
> But now these equations have different arities, and its rejected by
> Haskell. Why does this not simply desugar to:
> 
> f [] = [1]
> f x = (sort . nub) x
> 
> i.e. lift the arities to the longest argument list.
> 
> Is there a reason this isn't done?
> 
Answer #2:

Because you can't write

f x = case x of
	[] -> [1]
        -> sort.nub


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