[m-dev.] Feature request via Google+

Julien Fischer jfischer at opturion.com
Sat Nov 30 02:19:12 AEDT 2013

On Fri, Nov 29, 2013 at 10:56 PM, Paul Bone <paul at bone.id.au> wrote:

> On Google+ an entity named JekejekeLogicProgramming asked the following.
>     Dear All,
>     I am just reading:
> http://www.mercurylang.org/information/doc-latest/mercury_ref/Trailing.html#Trailing
>     Is there a Prolog API for the trailing. So that I can use functional
>     trailing  from within Prolog without much C programming. I only need
> to be
>     able to install a Prolog goal which is called once when the trail does
> an
>     undo.
>     Best Regards
> I asked him to confirm what he meant by Prolog, he meant Mercury.
> It should be possible to make this accessible through Mercury, provided
> that
> trail predicates are either allowed to be impure, or take an io state pair.
> Registering such predicates should have similar rules, which won't be
> onerous as the programmer will already need the io state or impurity for
> trailing to make sense at all.
> Is anyone aware of any problems with this?

We've had a module in G12 platform that provides exactly this interface to
the trail
for about six years now ;-)  I'm happy to make this available to others if
is some need for it -- it requires some minor editing to detach it from the
rest of
G12, but that shouldn't take long.

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