[Haskell-cafe] Alex -g

[Mihai Maruseac]

On Sun, Feb 20, 2011 at 10:20 PM, Max Bolingbroke
<batterseapower at hotmail.com> wrote:
> On 20 February 2011 19:56, Mihai Maruseac <mihai.maruseac at gmail.com> wrote:
>> Hi,
>>
>> When running Alex -g I get several warning telling me that a bang
>> pattern is required and that the warning will be an error in GHC 6.14.
>
> As it happens, that is not an error in GHC 7 (see
> http://hackage.haskell.org/trac/ghc/ticket/3278):
>
> """
> $ ghci -XMagicHash
> GHCi, version 7.0.1.20101215: http://www.haskell.org/ghc/  :? for help
> letLoading package ghc-prim ... linking ...  done.
> Loading package integer-gmp ... linking ... done.
> Loading package base ... linking ... xdone.
> Loading package ffi-1.0 ... linking ... done.
> Prelude> let x = 2# in 10
>
> <interactive>:1:5:
>    Warning: Bindings containing unlifted types should use an
> outermost bang pattern:
>               x = 2#
>    In the expression: let x = 2# in 10
>    In an equation for `it': it = let x = 2# in 10
>
> <interactive>:1:5:
>    Warning: Bindings containing unlifted types should use an
> outermost bang pattern:
>               x = 2#
>    In the expression: let x = 2# in 10
>    In an equation for `it': it = let x = 2# in 10
> 10
> """
>
> (I'm not quite sure why I get two identical warnings..)
>
> It looks like Alex has gone back and forth on what to do here. Selected commits:
>
> """
> Fri Nov 26 10:43:42 GMT 2010  Simon Marlow <marlowsd at gmail.com>
>  * don't use CPP for LANGUAGE pragmas
>  Drop the -fno-warn-lazy-unlifted-bindings again.  CPP in the header
>  prevents the user from adding their own LANGUAGE pragmas at the top of
>  the .x file if they're using GHC < 7.0.
>
> Wed Nov 17 10:42:23 GMT 2010  Simon Marlow <marlowsd at gmail.com>
>  * Stop using -fglasgow-exts, and turn off bogus bang-pattern warnings
>
> Wed Nov 17 10:41:06 GMT 2010  Simon Marlow <marlowsd at gmail.com>
>  * remove bang patterns on unlifted bindings again
>
> Wed Jun  3 23:58:54 BST 2009  Ian Lynagh <igloo at earth.li>
>  * Use bang patterns on unlifted bindings
> """
>
> So it looks like you should just ignore this warning, or turn it off :-)
>

Thanks :)