I think lumping all these extensions under one switch is the problem.
Yep, I agree. Would it be hard to split `-fglasgow-exts' up? I'd greatly appreciate a more fine-grained control here.
The only difficulty is that we don't have an easy way to parameterise the parser, since it's generated from a fixed grammar. It might be possible to do it by having multiple entry points to the parser, sharing as much of the grammar as possible, but I haven't tried (it sounds a bit sledgehammerish). We can often do optional syntax by parameterising the lexer, however: in fact there are already four switches that affect the syntax (-fglasgow-exts, -farrows, -fwith, -fffi). These generally work by turning on or off certain keywords (eg. -fffi turns on the 'foreign' keyword), which is usually all you need. Bottom line: yes in most cases you can give separate extensions their own flags. We're starting to move in that direction for new extensions, and if we get around to it we might separate some of the existing extensions. Cheers, Simon