Hello Matthias,
you may want to have a look at section 11 of my monads tutorial [1],
which contains monadic library functions like replicateM together with
examples and detailed explanations.
[1] http://ertes.de/articles/monads.html#section-11
Greets,
Ertugrul.
Matthias Guedemann
Hi,
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]
Now I want to make it capable to create all combinations of length n instead of fixed length 3 (that's why list instead of tuple), but I don't really see how. As the do notation translates to
ls >>= \a -> etc.
I thought it should be possible to have some sort of "foldr (>>=)" over a list of length n, but I can't figure out how to collect the variable number of results in a list for the "return".
Any hints for that?
best regards Matthias
-- nightmare = unsafePerformIO (getWrongWife >>= sex) http://blog.ertes.de/