Re: What are the preconditions of newArray#

Right. That's an option. On Tue, Aug 23, 2011 at 10:31 PM, Simon Marlow wrote:

You could make it a precondition of copyArray#, although that's slightly less pleasant from a user's perspective.

Cheers,        Simon

On 23/08/11 21:04, Johan Tibell wrote:

...

It could well be that it's some later primop that's failing due to the empty size, like my new copyArray# primop. If that's the case I could fix it but I would probably would have to add a branch to the copyArray# primop, which I'm reluctant to do.

On Tue, Aug 23, 2011 at 9:47 PM, Simon Marlow  wrote:

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An Array# of size zero is a perfectly reasonable thing.  If it doesn't work, it should (and I vaguely recall making it work at some point in the past, but perhaps I failed to add a test and as a result it has rotted...)

Cheers,        Simon

On 22/08/11 17:08, Johan Tibell wrote:

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I agree (unless it has a performance cost). I had to fix a couple of bugs in my code associated with generating zero-length arrays.

On Mon, Aug 22, 2011 at 5:54 PM, Edward Kmett  wrote:

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It would still be nice to have a consistent base case.

On Mon, Aug 22, 2011 at 3:43 AM, Johan Tibell wrote:

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On Mon, Aug 22, 2011 at 5:55 AM, Edward Z. Yang  wrote: > > stg_newArrayzh in rts/PrimOps.cmm doesn't appear to give any > indication, > so this might be a good patch to add.  But I'm curious: what would > allocating Array#s of size 0 do? Null pointers? That sounds > dangerous...

I would imagine that a zero sized array would be a StgArrPtrs header with its size field set to 0. It's not a very useful thing to have, I admit. If someone (Simon?) can confirm that we don't intend to support zero-length array I'll push a patch that adds a comment.

Johan

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