Hi, Am Freitag, den 04.04.2008, 22:44 +0100 schrieb Neil Mitchell:
Hi
We can however write function like this:
eqLengths [] [] = True eqLengths (x:xs) (y:ys) = eqLengths ys xs eqLengths _ _ = False
which looks just fine for me.
I have this defined function. I also have lenEq1, lenGt1, and a few other variants. It works, but it just doesn't feel elegant.
Note: In case anyone gets the wrong impression, I am not suggesting lazy naturals be the standard numeric type in Haskell, just that by not going that way we have paid a cost in terms of elegance.
How about something like this:
data Length a = Length [a]
instance Ord (Length a) where > compare (Length []) (Length []) = EQ > compare (Length []) (Length (_:_)) = LT > compare (Length (_:_)) (Length []) = GT > compare (Length (_:xs)) (Length (_:ys)) = compare (Length xs) (Length ys)
> instance Eq (Length a) where > l1 == l2 = compare l1 l2 == EQ then you can do at least lazy lengths comparisons relatively nice by writing
if Length list1 >= Length list2 then print "list1" else print "list2"
(just a quick idea) Greetings Joachim -- Joachim Breitner e-Mail: mail@joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata@joachim-breitner.de