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|
-- | This module currently asserts that we give functions that always return
-- the same constructor of a sum type the CPR property.
module T5075 where
-- Omission of the type signature is deliberate, otherwise we won't get a join
-- point (this is up to the desugarer, not sure why).
-- f :: (Ord a, Num a) => a -> Either a b
f x = case x < 10 of
True -> Left x
False -> f (x*2)
-- Similarly a join point. Should WW nonetheless
g :: Int -> Int -> Maybe Int
g x y = go x
where
go x = case x < y of
True -> Just x
False -> go (x*2)
-- Here, go is not a join point, but still should be WW'd for Just.
-- Unfortunately, CPR can't see that (+?) returns Just, so h won't get the CPR
-- property. It probably could by only considering the @Just@ case of the
-- inlined (+?).
h :: Int -> Maybe Int
h x = go x +? go (x+1)
where
Just x +? Just y = Just (x + y)
_ +? _ = Nothing
go z
| z > 10 = Just (x + z)
| otherwise = go (z*2)
|
