#4978: Continuation passing style loop doesn't compile into a loop
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Reporter: tibbe | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by tibbe):
Actually, I can unbox `Buffer` by redefining `empty` like so:
{{{
empty :: Builder
empty = Builder (\ k b -> b `seq` k b)
{-# INLINE empty #-}
}}}
That gives me a "perfect" loop in the previous example. However,
redefining `empty` in the real `Data.Binary.Builder` module doesn't work.
The extra `seq` gets in the way of the arity analysis. I've attached
`Repro3.hs`, which is very similar to the code I posted previously except
that now includes code to allocate a new buffer when needed (that part was
stubbed out in the above example).
If I don't add the `seq` to `empty` the arity analysis works, but `Buffer`
gets passed around boxed. If I add the `seq` I get an unboxed `Buffer`,
but the arity analysis fails and I get a closure allocated on each
iteration of the loop.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4978#comment:6>
GHC <http://www.haskell.org/ghc/>
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