Replace a 3 parameter list-comprehension by using map, concat

Question

I have some understanding of list comprehension. I understand that the expression:

[x * x | x <- [1..10]]
should output [1,4,9,16,25,36,49,64,81,100]
         


        

Answer 1

[(x,y+z) | x <- [1..10], y <- [1..x], z <- [1..y]]

is the same as

concatMap
    (\x -> [(x,y+z) | y <- [1..x], z <- [1..y]])
    [1..10]

You can extract the y and z variables out of the list comprehension similarly. (But you must do it in order from left to right: so y next and z last.)

concatMap is a function defined in the Prelude:

concatMap :: (a -> [b]) -> [a] -> [b]
concatMap f = concat . map f