content: --------------------------------------------------------------------------------
  -- MIT License
  --
  -- Copyright (C) 2024 Duck McSouls <quacksouls [AT] gmail [DOT] com>
  --
  -- Permission is hereby granted, free of charge, to any person obtaining a copy
  -- of this software and associated documentation files (the "Software"), to deal
  -- in the Software without restriction, including without limitation the rights
  -- to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  -- copies of the Software, and to permit persons to whom the Software is
  -- furnished to do so, subject to the following conditions:
  --
  -- The above copyright notice and this permission notice shall be included in
  -- all copies or substantial portions of the Software.
  --
  -- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  -- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  -- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  -- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  -- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  -- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  -- SOFTWARE.
  --------------------------------------------------------------------------------
  
  import Text.Printf
  
  -- | The first elements in a list of 2-tuples.
  first :: [(a, b)] -> [a]
  first xs = [x | (x, _) <- xs]
  
  -- | The second elements in a list of 2-tuples.
  second :: [(a, b)] -> [b]
  second xs = [y | (_, y) <- xs]
  
  -- | The elements of a list of 2-tuples.
  main = do
      let a = [(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd'), (5, 'e')]
      let b = [(x, y) | x <- [1 .. 5], y <- [6 .. 10]]
      let c = [(a, b) | a <- "abcdef", b <- "ghij"]
      putStrLn "First elements"
      printf "%s -> %s\n" (show a) $ show . first $ a
      printf "%s -> %s\n" (show b) $ show . first $ b
      printf "%s -> %s\n" (show c) $ show . first $ c
      putStrLn "\nSecond elements"
      printf "%s -> %s\n" (show a) $ show . second $ a
      printf "%s -> %s\n" (show b) $ show . second $ b
      printf "%s -> %s\n" (show c) $ show . second $ c
  