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module Main where
{-# NOINLINE foo #-}
foo :: Int -> Int
foo x = x
{-# RULES "foo/5" forall (f :: Int -> Int). foo (f 5) = foo (f 42) #-}
-- highly suspect, of course!
main = print $ foo (let {-# NOINLINE j #-}
j :: Int -> Int
j n = n + 1 in j 5)
{-
If we're not careful, this will get rewritten to
main = print $ let <join> j n = n + 1 in foo (j 42)
which violates the join point invariant (can't invoke a join point from
non-tail context). Solution is to refuse to float join points when matching
RULES.
-}
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