Hi
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?
I like it!
* If you want to load one of the modules in ghci, say, then you need to tell it what flags to use.
I think this is the killer reason. Another reason that you don't mention is that it discourages the use of extensions, not massively, but slightly. Now if you want to use a particular extension lots you must specify it in every single file. Thanks Neil