CPP Help (was Re: Latest Template Haskell Breaks Package)

Ok I have a cut down version of the problem and am cross posting to glasgow-haskell-users. To restate the problem: this is from code that has not been changed for 2 years. I get

Examples.hs:42:42: Parse error in pattern: con Failed, modules loaded: none.

Any help would be very gratefully received.

{-# LANGUAGE TypeFamilies, MultiParamTypeClasses, FunctionalDependencies #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE EmptyDataDecls #-} {-# LANGUAGE FlexibleInstances, TypeSynonymInstances #-} {-# LANGUAGE UndecidableInstances, OverlappingInstances #-} {-# LANGUAGE GeneralizedNewtypeDeriving, StandaloneDeriving #-} {-# LANGUAGE RankNTypes, ScopedTypeVariables #-} {-# LANGUAGE MagicHash, BangPatterns, UnboxedTuples #-} {-# LANGUAGE TemplateHaskell, CPP #-}

module Examples where

import GHC.Prim import GHC.Exts import GHC.Types import GHC.Word import GHC.Int

class Touchable a where touch :: a -> IO ()

instance Touchable Bool where touch b = IO (\s -> case touch# b s of s' -> (# s', () #)) {-# INLINE touch #-}

#define TOUCHABLE_INST(ty,con) \ instance Touchable ty where { \ touch (con x#) = IO (\s -> case touch# x# s of s' -> (# s', () #)); \ {-# INLINE touch #-}; \ }

TOUCHABLE_INST(Int, I#)

#define PRIM_COMP_INST(ty,con,le,ge) \ instance PrimitiveOrd ty where { \ minM' (con a#) (con b#) = \ IO (\s -> \ let r# = if le a# b# then a# else b# \ in case touch# r# s of s' -> (# s', (con r#) #)); \ }

PRIM_COMP_INST(Int, I#, (<=#), (>=#))

Dominic Steinitz dominic@steinitz.org http://idontgetoutmuch.wordpress.com On 23 Dec 2014, at 15:06, Dominic Steinitz wrote:

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-Prim...

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@steinitz.org http://idontgetoutmuch.wordpress.com

On 23 Dec 2014, at 13:42, Erik Hesselink 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 wrote:

...

I realise I should have sent this to the libraries list.

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

Begin forwarded message:

From: Dominic Steinitz Subject: Latest Template Haskell Breaks Package Date: 23 December 2014 13:14:26 GMT To: Haskell-Cafe

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/ccd7891c536b... 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

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