All combinations of elements of two lists in Haskell

Question

Given two lists, [a, b] and [c, d], I\'d like to get the following result:

[(a,c), (a,d), (b         


        

Answer 1

Applicative style all the way!

λ> :m + Control.Applicative
λ> (,) <$> ['a','b'] <*> ['c','d']
[('a','c'),('a','d'),('b','c'),('b','d')]

(I've eschewed any String syntactic sugar above, in order to stay close to your example.)

For information, (,) is special syntax for a function that takes two arguments and makes a pair out of them:

λ> :t (,)
(,) :: a -> b -> (a, b)

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Edit: As noted by leftaroundabout in his comment, you can also use liftA2:

λ> :m + Control.Applicative
λ> let combine = liftA2 (,)
λ> combine "ab" "cd"
[('a','c'),('a','d'),('b','c'),('b','d')]