On 2006-01-26, Olaf Chitil
I am very please to see on the Wiki also a list of removal candidates and that these include n+k patterns and ~ patterns.
I'd like to add one pattern to this list of removal candiates: k patterns, that is, numeric literals.
I don't see that much use for the first two but I really want to argue for being able to pattern-match on numeric literals. I think numeric literals should be treated as much as possible as if there were declarations like "data Int = 0 | 1 | (-1) | 2 | (-2) | ..." Or am I misunderstanding the suggestion here?
Iff n+k patterns are removed, there is little good use for k patterns either.
Say what? n+k could perhaps serve some pedagogical purpose in presenting the peano numbers. Plain old literals are not so tied to a particular representation (that is, you can imagine 4 being expanded to match Int# 4, or BooleanSequence [T,F,F] internally, or whatever and still looking exactly the same in the code), and have the same utility as being able to pattern-match any data.
So get rid of these three and pattern matching becomes so much more simple.
From the point of view of Hat, yes. Despite how useful hat is, I'd rather have the ability to do
ack 0 n = n+1 ack m 0 = ack (m-1) 1 ack m n = ack (m-1) (ack m (n-1)) which looks far nicer than ack m n | m == 0 = n + 1 | n == 0 = ack (m-1) 1 | otherwise = ack (m-1) (ack m (n-1)) I admit this is 99% aesthetics, but aesthetics do matter, as does consistency and regularity. And there are some cases where the guards can get quite complex, especially when rewriting something that already combines pattern-matching with guards. -- Aaron Denney -><-