[m-rev.] for review: Document actual behaviour of mvar.try_take and mvar.try_read.

[Julien Fischer]

On Fri, 17 Apr 2020, Peter Wang wrote:

> I still need to think more about this one.
> ---
>
> library/thread.mvar.m:
>    Document actual behaviour of mvar.try_take and mvar.try_read:
>    both may return `no' even if the mvar was not empty.
>
>    Clarify behaviour of mvar.read.
>
> NEWS:
>    Announce change.

That's fine.

Julien.