HEADS-UP: diagrams does not compile with HEAD (regressions)

Reid Barton rwbarton at gmail.com
Tue Jun 10 14:53:54 UTC 2014

I expect this is a result of https://ghc.haskell.org/trac/ghc/ticket/8883,
but even so it's not clear to me whether the error is correct. It would be
nice if GHC printed the type it inferred for succ' in this kind of

Reid Barton

On Tue, Jun 10, 2014 at 7:55 AM, Gabor Greif <ggreif at gmail.com> wrote:

> Devs,
> as of recently GHC HEAD stopped building the diagrams library. Several
> prerequisite libs also fail to compile. A specific error message
> appears in an attoparsec issue
> <https://github.com/bos/attoparsec/issues/67>, for which I have
> submitted a workaround. But as Herbert cautiously points out, this
> could be a recent GHC bug surfacing.
> The symptoms of the bug seem to be that GHC complains about the usage
> of (~) type equality operation, but there is no reference to that type
> operator in the source code. To work around the problem it suffices to
> add -XGADTs or -XTypeFamilies.
> Does this ring any bells? Can automatized tests catch such things in the
> future?
> Cheers,
>     Gabor
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