On Fri, Oct 30, 2009 at 12:44 PM, Matthias Guedemann
a friend of mine wanted to write function (in Perl) that creates all tuples of length 3 of the elements of a given list, e.g. [(0,0,0),(0,0,1),(0,0,2),...,(5,5,5)] for the list [0..5]. Trying to get better at Haskell, I wrote a small function using the list monad for this (tuples replaced with lists)
all3 ls = do a <- ls b <- ls c <- ls return [a,b,c]
Almost there : all3 ls = do a <- ls b <- ls c <- ls return (a,b,c) For each element a of list ls , for each element b of the same list ls, and for each element c of the same list ls, make a tuple of them. return the list of tall the tuples. You could also write it with a list comprehension : all3 ls = [ (a,b,c) | a <- ls, b <- ls, c <- ls ] David.