On Mon, 2008-11-10 at 16:06 -0600, Derek Elkins wrote:
On Mon, 2008-11-10 at 18:50 +0000, Duncan Coutts wrote: [...]
If you meant, why is it allowed rather than banned then I guess the answer is because it is orthogonal. The rules naturally handle that case and there was no particular reason to ban it, even if it is somewhat unusual.
"Unusual?" This is the motivation of list comprehensions.
In naive set theory, set comprehensions are one way of an equivalence between predicates and sets. It's the Cartesian product aspect that should be considered unusual if anything.
Well, the Cartesian product case is one way of an equivalence between relations and sets of pairs. So I don't think it [ (x, y) | x <- xn, y <- ys ] is any more unusual than [ x | x <- xn ] jcc