[Haskell-cafe] Skolems!

[Brandon Allbery]

On Mon, Jan 26, 2015 at 4:54 PM, Bertram Felgenhauer <
bertram.felgenhauer at googlemail.com> wrote:

> Tom Murphy wrote:
> > So it's the "(rigid, skolem)" error you sometimes happen across. The code
> > that's causing it, though, is pretty unsuspicious:
>
> Just two clues, pointing towards `b` being monomorphic as one
> ontributing factor:
>
> * adding {-# LANGUAGE NoMonoLocalBinds #-} works.
> * giving `b` a standalone type signature makes it work, that is:
> (...)
> I'm not sure how enabling GADTs affects type-checking here.
>

See
https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/other-type-extensions.html#mono-local-binds

In particular:
"The flag -XMonoLocalBinds is implied by -XTypeFamilies and -XGADTs. You
can switch it off again with -XNoMonoLocalBinds but type inference becomes
less predicatable if you do so."

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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