Latest Template Haskell Breaks Package

[Dominic Steinitz]

Hi Erik,

Thank you very much. With that clue the compilation now doesn’t fail at that particular point.

The bad news is it now fails to compile this module

https://hackage.haskell.org/package/yarr-1.3.2/docs/src/Data-Yarr-Utils-Primitive.html#clampM%27

with a parse error(!). Not only do I not have much experience with TH but this has now exposed my ignorance of CPP.

> Data/Yarr/Utils/Primitive.hs:119:126: Parse error in pattern: con

If I comment out the last four lines

> PRIM_COMP_INST(Int, I#, (<=#), (>=#))
> PRIM_COMP_INST(Char, C#, leChar#, geChar#)
> PRIM_COMP_INST(Word, W#, leWord#, geWord#)
> PRIM_COMP_INST(Double, D#, (<=##), (>=##))
> PRIM_COMP_INST(Float, F#, leFloat#, geFloat#)

then the module compiles but of course then the whole package does *not* compile.

Did something change in 7.8.3 with regard to CPP (this code has not been modified for at least two years)?

Thanks once again.

Dominic Steinitz
dominic at steinitz.org
http://idontgetoutmuch.wordpress.com

On 23 Dec 2014, at 13:42, Erik Hesselink <hesselink at gmail.com> wrote:

> Hi Dominic,
> 
> It looks like just a representation change: a TySynEqn is a data type
> containing a [Type] and a Type, and those were the original two
> arguments. So it looks like with a little bit of CPP, you could
> support both versions. Something like
> 
> #if MIN_VERSION_template_haskell(2,9,0)
> ...
> #else
> ...
> #endif
> 
> In general, I think each major release of template haskell has quite
> some breaking changes, but I don't know of any place where they're
> enumerated. The GHC changelog only has a couple of high level bullet
> points.
> 
> Regards,
> 
> Erik
> 
> On Tue, Dec 23, 2014 at 2:20 PM, Dominic Steinitz <dominic at steinitz.org> wrote:
>> I realise I should have sent this to the libraries list.
>> 
>> Dominic Steinitz
>> dominic at steinitz.org
>> http://idontgetoutmuch.wordpress.com
>> 
>> Begin forwarded message:
>> 
>> From: Dominic Steinitz <dominic at steinitz.org>
>> Subject: Latest Template Haskell Breaks Package
>> Date: 23 December 2014 13:14:26 GMT
>> To: Haskell-Cafe <haskell-cafe at 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 at steinitz.org
>> http://idontgetoutmuch.wordpress.com
>> 
>> 
>> 
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