[Pkg-haskell-maintainers] Bug#635113: Generated code fails to compile: uses bang patterns without corresponding {-# LANGUAGE BangPatterns #-} pragma

Erik de Castro Lopo erikd at mega-nerd.com
Sat Jul 23 01:26:10 UTC 2011

Josh Triplett wrote:

> That looks like Alex's own lexer, used to build Alex; adding
> BangPatterns there seems like the wrong fix, and it *only* fixes Alex
> itself, not other users of Alex. 

Ah, right. 

> Instead, Alex should automatically add
> {-# LANGUAGE BangPatterns #-} to the generated lexer (or rather, extend
> the existing LANGUAGE pragma to include BangPatterns) when it uses
> BangPatterns (specifically, when using -g).  That would avoid forcing
> the project that uses Alex to know that it needs BangPatterns
> internally.

Ok, I'll purse that issue.

> Projects using Cabal automatically invoke alex with -g when building
> with GHC, so this change breaks any project using Cabal and Alex (or any
> other project using -g).  A quick search turns up various build logs
> (from Debian packages and otherwise) of lexers failing to build with
> this error.
> Also, I hope that the fixed version of this patch can go upstream to fix
> other users of alex, since otherwise a project building on Debian and
> using -Wall -Werror will fail to build when not using Debian alex.

I have definitely tried:


Apparently this will be fixed in ghc-7.2 which should be released
around september this year.

Erik de Castro Lopo

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