ranjitjhala
commented
4 years ago Hmm, interesting, thanks for letting me know!
It's also further puzzling to me that the below is SAFE
{-@ aaaa :: Int -> Maybe {y:Int | y > 0} @-}
aaaa :: Int -> Maybe Int
aaaa dim
| test dim = Just dim
| otherwise = Nothing
where
test :: Int -> Bool
test dim = dim > 0but that the following variant is UNSAFE
{-@ aaaa :: Int -> Maybe {y:Int | y > 0} @-}
aaaa :: Int -> Maybe Int
aaaa dim = if test dim then Just dim else Nothing
where
test :: Int -> Bool
test dim = dim > 0I wonder if it has to do with how GHC core gets generated for the two cases.
I will file this as an LH issue! thanks!
rosekunkel
I was trying to figure out how to make my code safe and then I try to isolate the problem when I stumbled upon a curious case.
I make this code and it's unsafe as expected. But then I try to tinker around the code and it results in this code which is safe! Eventhough
aaaaactually doesn't change at all, adding an irrelevant function which just so happens to have an exact definition with the function inWhereinaaaamakes it safe somehow.I eventually found out that you need to make a specification also for the function defined in Where (in this case
{-@ test :: (Ord a, Num a) => x:a -> {y:Bool | y <=> (x > 0)} @-}) to make the function passed safe but this particular case still seems like an odd behavior to me.