[Haskell-cafe] Re: Polyvariadic functions operating with a monoid

Kevin Jardine kevinjardine at gmail.com
Sat Oct 9 08:28:25 EDT 2010

Hi Bartek,

Yes, it compiles, but when I try to use polyToMonoid', it turns out
that this function is no longer polyvariadic, unlike the original
polyToMonoid .

This may be what Luke meant when he wrote "you lose composability".

Even with the extra unwrap function I think that this is pretty cool,
but I would ideally like to hide the unwrap.


On Oct 9, 1:50 pm, Bartek Ćwikłowski <paczesi... at gmail.com> wrote:
> Hello Kevin,
> 2010/10/9 Kevin Jardine <kevinjard... at gmail.com>:
> > I was attempting to turn this into a small library and wanted to avoid
> > exporting unwrap.
> > I defined:
> > polyToMonoid' = unwrap . polyToMonoid
> If you disable MonomorphismRestriction this definition typechecks just
> fine. Alternatively, you can ask ghci about the type of "unwrap .
> polyToMonoid" and paste that into the type sig.
> regards,
> Bartek Ćwikłowski
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