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
  
  -- | Integer exponentiation.
  pow :: Integer -> Integer -> Integer
  pow 0 0 = 1
  pow 0 _ = 0
  pow _ 0 = 1
  pow a n
      | n < 0 = error "Must be positive integer"
      | otherwise = a * pow a (n - 1)
  
  -- | Integer exponentiation.
  main = do
      let a = 2 :: Integer
      let b = -7 :: Integer
      let c = 0 :: Integer
      let d = 3 :: Integer
      let test1 = pow a c == a ^ c
      let test2 = pow c c == c ^ c
      let test3 = pow c a == c ^ a
      let test4 = pow a d == a ^ d
      let test5 = pow b d == b ^ d
      printf "%d^0 -> %d: %s\n" a (pow a c) $ show test1
      printf "0^0 -> %d: %s\n" (pow c c) $ show test2
      printf "0^%d -> %d: %s\n" a (pow c a) $ show test3
      printf "%d^%d -> %d: %s\n" a d (pow a d) $ show test4
      printf "%d^%d -> %d: %s\n" b d (pow b d) $ show test5
  