Hi Jan, On Tue, Apr 09, 2013 at 01:32:33PM +0200, Jan Stolarek wrote: > Thanks for pointing me to earlier discussions on this subject - they are > enlightening :) One > particular argument "against" seems to be very convincing to me: > > "From a language design point of view, it should be noted that turning > non-left linear patterns into ones with == guards elevates the class Eq > to built-in status - but the compiler has no semantic control over it."
Yes, I can see the point, but in the case of Haskell with its ability to automatically derive the Eq instance, there's some kind of semantic control, and if an user writes a nonsense Eq instance, than he just really asks for some hurting ;). > Regarding the possibility of making accidental mistakes during refactoring > etc. This could be > implemented as a language extension, requiring explicit LANGUAGE pragma. So > people using it would > know they have semantics slightly changed and need to be aware that there is > a possibility of > making these kind of mistakes. I'm a bit torn between all these GHC extensions. If your code doesn't compile, did you really made a mistake or just forgot to include a GHC extension ... But I also have the feeling, that the extension perhaps might not be worth it, because the difference between foo x x = ... and foo x y | x == y = ... is just IMHO too small. Greetings, Daniel _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
