Extensions and Cabal

Ian Lynagh igloo at earth.li
Sat Mar 24 19:24:00 EDT 2007

On Sat, Mar 24, 2007 at 10:53:54PM +0000, Samuel Bronson wrote:
> Ian Lynagh <igloo <at> earth.li> writes:
> > Thus I propose that the .cabal file actually specifies what extensions
> > the modules are /allowed/ to use, but does not actually enable them.
> > They would then be enabled by LANGUAGE pragmas in the modules as
> > necessary. So, if the .cabal file says "Extensions: E, F" then the
> > modules will be compiled with
> >     --no-extension-flags --allowed-extension=E,F
> > and if a module has "{-# LANGUAGE E #-}" then only extension E would be
> > enabled for that module. If a module has "{-# LANGUAGE E,G #-}" then
> > compilation would fail as extension G is not permitted.
> > 
> > Any comments? Criticisms? Flames?
> The only thing I can think of (besides "nice idea") is that you'd better either
>  a) make sure that Cabal always knows about all the extensions supported by the
> compiler
> or
>  b) provide a workaround for when Cabal does not know about a given extension.

That's the --language=E flag in the paragraph beginning "2 and 4".

But actually, Cabal would no longer enable extensions with this flag
anyway, it would just list the extensions after the --allowed-extension
flag (and it doesn't need to recognise them to list them).


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