twhitehead:
On Thursday 16 October 2008 07:03:05 Roman Leshchinskiy wrote:
On 16/10/2008, at 21:34, Simon Peyton-Jones wrote:
BUT people who care probably UNPACK their strict fields too, which is even better. The time you can't do that is for sum types data T = MkT ![Int]
You also can't do it for polymorphic components. I've used code like:
data T a = MkT !a
foo :: T (a,b) -> a foo (MkT (x,y)) = x
Here, unpacking doesn't work but foo could still access the components of the pair directly.
This is actually the situation I was originally looking at. I just simplified it for the sake of posting readable core and assembler.
Specifically, I was looking at some of the assembler GHC was generating for some array code to see if it could do a clean enough job to be used instead of C, and was finding this sort of thing because STUArrau is defined as
data STUArray s i a = STUArray !i !i !Int (MutableByteArray# s)
FWIW, I get much nicer code with uvector (which uses type families to select monomorphic instances of things, and aggressive inlining, to yield much better code in practice). The DPH arrays library uses a similar method. So you might make some progress by taking that direction. -- Don