Main.hs

import qualified Control.Monad as Monad
import qualified Flow
import qualified System.Exit as Exit
import qualified Test.HUnit as Test

main :: IO ()
main = do
  counts <- Test.runTestTT $ Test.TestList
    [ True Test.~?= True
    , (3 Flow.|> succ Flow.|> recip Flow.|> negate) Test.~?= (-0.25 :: Double)
    , (negate Flow.<| recip Flow.<| succ Flow.<| 3) Test.~?= (-0.25 :: Double)
    , map (Flow.apply 2) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    , map (\ f -> 2 Flow.|> f) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    , map (2 Flow.|>) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    , map (Flow.<| 2) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    , map (Flow.apply 3) (map (Flow.compose succ) [recip, negate]) Test.~?= [0.25, -4 :: Double]
    , (succ Flow..> recip Flow..> negate) 3 Test.~?= (-0.25 :: Double)
    , (negate Flow.<. recip Flow.<. succ) 3 Test.~?= (-0.25 :: Double)
    , map (\ f -> f 3) (map (\ f -> succ Flow..> f) [recip, negate]) Test.~?= [0.25, -4 :: Double]
    , map (\ f -> f 3) (map (succ Flow..>) [recip, negate]) Test.~?= [0.25, -4 :: Double]
    , map (\ f -> f 3) (map (Flow.<. succ) [recip, negate]) Test.~?= [0.25, -4 :: Double]
    , (3 Flow.!> succ Flow.!> recip Flow.!> negate) Test.~?= (-0.25 :: Double)
    , (undefined Flow.|> const True) Test.~?= True
    , (negate Flow.<! recip Flow.<! succ Flow.<! 3) Test.~?= (-0.25 :: Double)
    , (const True Flow.<| undefined) Test.~?= True
    , map (Flow.apply' 2) [succ, recip, negate]  Test.~?= [3, 0.5, -2 :: Double]
    , Flow.apply undefined (const True) Test.~?= True
    , map (\ f -> 2 Flow.!> f) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    , map (2 Flow.!>) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    , map (Flow.<! 2) [succ, recip, negate] Test.~?= [3, 0.5, -2 :: Double]
    ]

  let
    hasErrors = Test.errors counts /= 0
    hasFailures = Test.failures counts /= 0
  Monad.when (hasErrors || hasFailures) Exit.exitFailure