From: Dominic Steinitz <dominic@steinitz.org>

Subject: Latest Template Haskell Breaks Package

Date: 23 December 2014 13:14:26 GMT

To: Haskell-Cafe <haskell-cafe@haskell.org>

Hello Fellow Haskellers,

I have become a maintainer for yarr (https://hackage.haskell.org/package/yarr). This no longer compiles with ghc-7.8.3 because it specifies base == 4.6. Relaxing this to base >=4.6 && <4.8 tells me I need a newer version of Template Haskell

rejecting: template-haskell-2.7.0.0, 2.6.0.0, 2.5.0.0, 2.4.0.1, 2.4.0.0,

2.3.0.1, 2.3.0.0, 2.2.0.0 (conflict: yarr => template-haskell>=2.8 && <2.9)

If I now relax the constraint for Template Haskell I get a compiler error as there has been a breaking change from Template Haskell 2.9 to 2.10.

Data/Yarr/Utils/FixedVector/VecTuple.hs:45:16:

    Couldn't match expected type ‘TypeQ -> Q Dec’

                with actual type ‘Q Dec’

    The function ‘tySynInstD’ is applied to three arguments,

    but its type ‘Name -> TySynEqnQ -> DecQ’ has only two

And indeed looking at the changes in http://git.haskell.org/packages/template-haskell.git/commitdiff/ccd7891c536b29b8bea96eb92520f46e21390e39 I can see that the function in question has changed.

-tySynInstD :: Name -> [TypeQ] -> TypeQ -> DecQ

-tySynInstD tc tys rhs = 

+tySynInstD :: Name -> [TySynEqnQ] -> DecQ

+tySynInstD tc eqns = 

Did I miss some announcement of this breaking change and the advice on what to do about it?

If I did can someone please point me at the relevant document. If not then I feel sad and would be very grateful if someone could help me as I know very little about Template Haskell.

Many thanks

Dominic Steinitz

dominic@steinitz.org

http://idontgetoutmuch.wordpress.com