Neither.hs

module Main where

{-# INLINE neither #-}
neither :: Bool -> Bool
neither = not

infixl `nor`
{-# INLINE nor #-}
nor :: Bool -> Bool -> Bool
nor x y = x && not y

-- | `Neither` for three inputs
neither3 :: Bool -> Bool -> Bool -> Bool
neither3 x y z = neither x `nor` y `nor` z

-- | What we expect `Neither` for three inputs to equal
expectedNeither3 :: Bool -> Bool -> Bool -> Bool
expectedNeither3 x y z = not x && not y && not z

-- | Assert `neither3` is equivalent to `expectedNeither3`
-- for all possible inputs
test :: Either String ()
test =
  sequence_
    [ if found == expected
      then Right ()
      else Left $
           unwords
             [ "Test failed:\nx:"
             , show x
             , "y:"
             , show y
             , "z:"
             , show z
             , "\nExpected:"
             , show expected
             , "but got:"
             , show found
             ]
    | let bools = [False ..]
    , x <- bools
    , y <- bools
    , z <- bools
    , let found = neither3 x y z
    , let expected = expectedNeither3 x y z
    ]

-- | Run test
main :: IO ()
main =
  case test of
    Right () -> putStrLn "All tests passed"
    Left err -> putStrLn err

-- » stack ghc -- Neither.hs -o neither
-- [1 of 1] Compiling Main             ( Neither.hs, Neither.o )
-- Linking neither ...
-- clang: warning: argument unused during compilation: '-nopie' [-Wunused-command-line-argument]
-- clang: warning: argument unused during compilation: '-nopie' [-Wunused-command-line-argument]
-- ./neither
-- All tests passed

-- » stack ghc -- --version
-- The Glorious Glasgow Haskell Compilation System, version 8.4.3