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-- !!! A rules test
-- At one time the rule got too specialised a type:
--
-- _R "ffoo" forall {@ a1 v :: (a1, ((), ()))}
-- fst @ a1 @ () (sndSnd @ a1 @ () @ () v) = fst @ a1 @ ((), ()) v
module Main where
import System.IO
import System.IO.Unsafe ( unsafePerformIO )
{-# NOINLINE [0] sndSnd #-}
-- Dont inline till last, to give the rule a chance
sndSnd (a,(b,c)) = (a,c)
trace x y = unsafePerformIO (hPutStr stderr x >> hPutStr stderr "\n" >> return y)
{-# RULES "foo" forall v . fst (sndSnd v) = trace "Yes" (fst v) #-}
main :: IO ()
main = print (fst (sndSnd (True, (False,True))))
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