[Haskell-cafe] Ambiguous type variable ‘f0’ arising from a use of ‘f’

Tom Ellis tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk
Sun Mar 20 21:38:04 UTC 2016

On Sun, Mar 20, 2016 at 05:36:42PM -0400, Richard Eisenberg wrote:
> On Mar 20, 2016, at 4:33 PM, Tom Ellis <tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:
> > According to Travis the old program compiled on 7.8 and 7.10.  It certainly
> > compiled on 7.6 on my local machine.  When was the change that made it break
> > introduced (and what was that change exactly)?
> The change was for 8.0, as part of the redesign of part of the typechecker
> to support TypeApplications.  The change in behavior that you're seeing
> here was not intentional, but was just a side effect of the redesign.  It
> was originally reported as a regression, but I'm pretty sure that your
> original program should have been rejected, according to my understanding
> of how the monomorphism restriction works.

Oh, so you're saying it used to work by accident?

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