content: --------------------------------------------------------------------------------
  -- MIT License
  --
  -- Copyright (C) 2023 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 length of a list.
  size :: [a] -> Int
  size []     = 0
  size (x:xs) = 1 + size xs
  
  -- | The length of a list, using a fold operation.
  sizef = foldr (\_ acc -> 1 + acc) 0
  
  -- | An implementation of "length".
  main = do
      let a = []
      let b = [1, 3, 5]
      let c = ["a", "b", "c", "d", "e"]
      let d = "dandelion"
      let testa = length a == size a && length a == sizef a
      let testb = length b == size b && length b == sizef b
      let testc = length c == size c && length c == sizef c
      let testd = length d == size d && length d == sizef d
      printf "[] -> %d: %s\n" (size a) $ show testa
      printf "%s -> %d: %s\n" (show b) (size b) $ show testb
      printf "%s -> %d: %s\n" (show c) (size c) $ show testc
      printf "%s -> %d: %s\n" (show d) (size d) $ show testd
  