index*OffAddr

[Simon Marlow]

On 21/04/2010 09:45, Roman Leshchinskiy wrote:

> After thinking about this for a while, I came up with two possible solutions. One is to provide a "pure" version of touch#:
>
>    use# :: o ->  o' ->  o'
>
> such that use# x y = y. This would change the code above to:
>
>    I# (use# arr# (indexIntOffAddr# addr# i#))
>
> I don't know how to implement this, though, because use# would have to be able to return arbitrary (unboxed) types and the code generator doesn't really seem to support this.
 >
> A perhaps simpler solution is to add a new set of primitives:
>
>    indexIntOffAddrUsing# :: o ->  Addr# ->  Int# ->  Int#
>    ...
>
> These would take an additional argument which they'd touch and otherwise ignore. The code would then become:
>
>    I# (indexIntOffAddrUsing# arr# addr# i#)

Seems like the way to go, I can't think of a better alternative.

> Incidentally, the index*OffAddr# primitives don't seem to be used anywhere.

There are a handful of uses in libraries/base, mainly GHC.Base.

Cheers,
	Simon