#4201: Improve eta reduction
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.12.3
Keywords: | Difficulty:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
Consider
{{{
-- bar :: Int -> Int
-- g :: Moo ~ Int
f :: (Moo -> Int) -> Char
foo f = f (\ x -> bar (x `cast` a))
}}}
This will allocate a closure for `(\ x -> bar (x `cast` a))` before
calling `f`. But really it should eta-reduce the lambda to
{{{
foo f = f (bar `cast` (sym g -> Int))
-- (sym g -> Int) :: (Int -> Int) ~ (Moo -> Int)
}}}
Result: no allocation before calling `f`.
Thanks to Louis for suggesting this http://www.haskell.org/pipermail
/glasgow-haskell-users/2010-July/018982.html
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4201>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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