On Thu, 2008-09-11 at 18:34 +0200, Johannes Waldmann wrote:
if support for this simple shape of dependencies ( ... | a -> b ) ...
For backwards-compatibility reasons,
Yes.
This gives point, then, to my concerns about letting Haskell become a practical language. At some point, production systems always seem to be end-of-lifed by backwards compatibility.
or because you think they're better than type families?
Don't know (haven't used them).
Concrete example: I have this "class Partial p i b | p i -> b" http://dfa.imn.htwk-leipzig.de/cgi-bin/cvsweb/tool/src/Challenger/Partial.hs...
What would type families buy me here?
I can't figure out what b is. I could, of course, argue that it would force you to come up with a name for `b', so people reading the code could understand what it does.
In my code, this class has tons of instances (I count 80). How much would I need to change them?
instance Partial p i b where => instance Partial p i type B p i = b And type signatures involving Partial would have to change.
Could this be automated?
To a certain extent. Finding the places that need to change could be automated, which is always the first step :) jcc