#1349: Generalise the ! and UNPACK mechanism for data types, to unpack function
arguments
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: task | Status: new
Priority: normal | Milestone: 6.12.3
Component: Compiler | Version: 6.6.1
Keywords: | Difficulty: Unknown
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by simonpj):
OK I get the idea. But there are a number of corners. For example:
* If I have a function of type `(!Int -> Int)` can I pass it to a
function expecting an argument of type `(Int -> Int)`. Perhaps yes, with
some automatic impedence matching?
* If there is automatic impedence matching might I lose sharing?
Example: suppose
{{{
f :: Int -> !Int -> Int
g :: (Int -> Int -> Int) -> Int
}}}
If GHC sees `(g f)` in source code, should it transform to `(g (\xy.
case y of I# y# -> g x y#))`? Tha might lose sharing if `(f x)` did a lot
of computation before returning a function.
* Does the type `!a -> a` make sense? It does for data constructors.
* An implementation question is this: how should these bang types be
represented? Is there a new type constructor for "!"? Is `(!Int -> Int)`
different to `(Int# -> Int)` or not?
A good framework to think of this in is Max's paper
[http://www.cl.cam.ac.uk/~mb566/papers/tacc-hs09.pdf Types are calling
conventions].
I doubt I'm going to move fast on this, I'm afraid.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1349#comment:22>
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