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 Data.Char
  import Data.Foldable
  import Text.Printf
  
  alphabet = "abcdefghijklmnopqrstuvwxyz"
  
  -- | Whether a sentence is a pangram.
  isPangram :: String -> Bool
  isPangram "" = False
  isPangram str = and $ map (\x -> x `elem` strLowercase) alphabet
    where
      strLowercase = lowercase str
  
  -- | Convert a string to all lowercase.
  lowercase :: String -> String
  lowercase str = map (\x -> toLower x) str
  
  -- | Is a sentence a pangram?
  main = do
      let sentence =
              [ ""
              , "1"
              , "abc"
              , "The quick brown fox jumps over the lazy dog."
              , "Waltz, bad nymph, for quick jigs vex."
              , "Glib jocks quiz nymph to vex dwarf."
              , "Sphinx of black quartz, judge my vow."
              , "How quickly daft jumping zebras vex!"
              , "The five boxing wizards jump quickly."
              , "Jackdaws love my big sphinx of quartz."
              , "Pack my box with five dozen liquor jugs."
              , "Mr Jock, TV quiz PhD, bags few lynx."
              ]
      for_ sentence $ \str -> do
          printf "%s -> %s\n" str $ show $ isPangram str
  