List as monad

In this recipe, we will revisit list and look at it as a monad. List is a monad, and we will work with a few examples of how to work with a list with monadic syntax and functions.

How to do it...

1. Create a new project list-as-monad using the simple Stack template.
2. Open src/Main.hs and edit it.
3. Add the following import for monad:

        import Control.Monad

4. Write a function that takes an integer x and returns a list of all integers starting with  x ([x, x+1, x+2,...]):

        nexts :: Num a => a -> [a]
        nexts x = do
        x : nexts (x+1)

5. Write a function that takes two lists and returns all ordered pairs from this list:

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

6. Write a partitioning function using list comprehension. The same function is also written using the monadic syntax:

        partition :: (a -> b -> Bool) -> [a] -> [b] -> [(a,b)]
        partition f xs ys = [ (x...