Splitting list into a list of possible tuples

Question

I need to split a list into a list of all possible tuples, but I\'m unsure of how to do so.

For example:

pairs [\"cat\",\"dog\",\"mouse\"]
         


        

Answer 1

Another possibility is to use monadic notation:

pairs :: (Eq a) => [a] -> [(a,a)]
pairs l = do
    x <- l
    y <- l
    guard (x /= y)
    return (x, y)

(The most general type for this definition of pairs would be (MonadPlus m, Eq a) => m a -> m (a,a) but I believe there is no instance of MonadPlus other than [] for which it would make sense.)