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

[Conal Elliott]

That eta-expansion desugaring would lose sharing.  Offhand, I don't know of
a desugaring that would do the trick and preserve sharing.  Any ideas?  -
Conal

On Jan 13, 2008 3:12 PM, 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?
>
> Thanks
>
> Neil
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