Am Dienstag, 17. Februar 2009 01:13 schrieb Martijn van Steenbergen:
Daniel Kraft wrote:
Do you think something would be especially nice to have and is currently missing?
Have type class aliases been implemented yet? This proposal (or parts or it) seems like a very useful compiler extension to have, and might be an interesting GSoC project.
http://repetae.net/recent/out/classalias.html
Kind regards,
Martijn.
It would be great to have something like class aliases implemented. However, the proposal(s) should be reviewed and discussed before someone starts implementing them. Once something is implemented, it is difficult to change it. It’s similar to libraries. Several libraries were implemented as part of research and their developers didn’t seem to think very deeply about choosing identifiers and such things. Later, these libraries were in wider use and changing the identifiers got problematic. I think of such things like the DPH identifiers. In my opinion, it’s bad practice to include single letters in identifiers to denote namespace. Parallel.filter would be much better than filterP. That said, I want to reinforce that class aliases are far too long not implemented. My dream is that we thoroughly improve library interfaces and class aliases could be important for doing so without breaking compatibility very much. So we should probably also think about what kinds of library interface changes would be desirable in order to know what features some class alias extension should provide. Some things that come to my mind immediately: * making Applicative a superclass of Monad * getting rid of MonadPlus (use (Alternative m, Monad m) instead of (MonadPlus m) or, with another extension, even something like (forall a. Monoid (m a), Monad m)) * getting rid of ugly Monoid method names (empty, append, concat or something totally different instead of mempty, mappend, mconcat) * redesigning numeric classes Best wishes, Wolfgang