inline_test.hs

{-# OPTIONS_GHC -fforce-recomp -ddump-simpl -fno-worker-wrapper -dsuppress-all #-}

module Main (main) where

import System.Environment (getArgs)

main :: IO ()
main = do
  [x,y] <- map read <$> getArgs
  let f1 = f x A B
      f2 = f y B f1
  print f2
 
data T = A | B | C | D | E | F | G
  deriving (Show)

{-# NOINLINE n #-}
n :: T -> T
n A = B
n B = C
n _ = A

f :: Int -> T -> T -> T
f sel x y =
    -- function large enough to avoid being simply inlined
    let j z = n . n . n . n . n . n $ z
    in case sel of
        -- j is always tailcalled
        0   -> j x
        _   -> j y