Haskell Cookbook

How it works...

The first function nexts shows that list is a monad. It uses the do notation and uses recursion to infinitely define the list.

The pairs function shows how the list monad works. The function is defined as follows:

    pairs :: [a] -> [b] -> [(a,b)]
    pairs xs ys = do
    x <- xs 
    y <- ys
    return (x,y)

It should read as follows: 

    for each x in xs     for each y in ys    create list of (x,y)    concatenate lists to return a single list

The list monad binds each element of a list to the function, creating another list, and concatenates them back together. The return function creates a singleton list.

The partition function is implemented in two ways. The list comprehension for partition is [(x,y) | x <- xs, y <- ys, f x y], which is a short form ...