GHCI usage example

Foo.hs

module Foo where

import Data.List

comparing :: (Ord a) => (b -> a) -> b -> b -> Ordering
comparing f x y = compare (f x) (f y)

sortByLength :: [[a]] -> [[a]]
sortByLength = sortBy (comparing length)

-- This file can be loaded with GHCI:
--  $ stack ghci Foo.hs
--
-- And then the function should be available:
--  *Foo> sortByLength [[1,2,3],[4,5],[4,5,6,7]]