fre 2002-08-16 klockan 15.37 skrev Andrew Koenig:
David> Oh, easily solved: "in the face of ambiguity, refuse the David> temptation to guess". There should be a best match rule, and David> if there are two best matches, it's an error.
In the ML example I showed earlier:
fun len([]) = 0 | len(h::t) = len(t) + 1
ordering is crucial: As long as the argument is not empty, both cases match, so the language is defined to test the clauses in sequence. My intuition is that people will often want to define category tests to be done in a particular order. There is no problem with such ordering as long as all of the tests are specified together.
What does "not empty" mean in this context? "not []"? Does h::t match [] or does [2] match []? Why is the ordering crucial? In Haskell: f [] = 0 f (x:xs) = 1 + f xs is totally equivalent with: f (x:xs) = 1 + f xs f [] = 0 Of course, if the different patterns overlap, THEN ordering is crucial, I just find it odd that [] and h::t would overlap... Martin -- Martin Sjögren martin@strakt.com ICQ : 41245059 Phone: +46 (0)31 7710870 Cell: +46 (0)739 169191 GPG key: http://www.strakt.com/~martin/gpg.html