content: --------------------------------------------------------------------------------
  -- MIT License
  --
  -- Copyright (C) 2024 Aaron Nguyen <mvngu [AT] gmx [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
  
  -- | A function that outputs a function to perform the usual arithmetic
  -- operations.
  math :: Integral a => String -> a -> (a -> a)
  math "+" x = \y -> x + y
  math "-" x = \y -> x - y
  math "*" x = \y -> x * y
  math "/" x = \y -> x `div` y
  math _ x   = \y -> y
  
  -- | A function that returns a function to perform arithmetics.
  main = do
      let a = 8 :: Integer
      let add3 = math "+" 3
      let decrement = math "-" 1
      let double = math "*" 2
      let dividend = math "/" 18
      let unknown = math "op" 42
      printf "increment 3 to %d -> %d\n" a $ add3 a
      printf "decrement %d -> %d\n" a $ decrement a
      printf "double %d -> %d\n" a $ double a
      printf "dividend %d -> %d\n" a $ dividend a
      printf "unknown op %d -> %d\n" a $ unknown a
  