N queens problem

[Jonata Goulart]

This is the problem to figure out the n queens problem but I didn't 
understand it very well.

Somebody can help me ?
how legal and queens functions work?

attack (l,c) (ll,cc) = l ==ll || (l+c==ll+cc) || (l-c==ll-cc)

legal p m = and [not (attack (l,c) (m, length p +1)) | (l,c) <- zip p [1..]]

queens n = r n n
                 where r 0 n = [[]]
                       r m n = [p ++ [m] | p <- r (m-1) n, m <-[1..n], legal 
p m]

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