[m-rev.] diff: reset contains_trace_goal if necessary

[Mark Brown]

On 06-Nov-2006, Zoltan Somogyi <zs at csse.unimelb.edu.au> wrote:
> @@ -2657,6 +2670,84 @@
>  
>  %-----------------------------------------------------------------------------%
>  
> +:- pred goal_contains_trace(hlds_goal::in, hlds_goal::out,
> +    contains_trace_goal::out) is det.
> +
> +goal_contains_trace(GoalExpr0 - GoalInfo0, GoalExpr - GoalInfo,
> +        ContainsTrace) :-
> +    (

	...

> +    ;
> +        GoalExpr0 = scope(Reason, SubGoal0),
> +        goal_contains_trace(SubGoal0, SubGoal, ContainsTrace),
> +        GoalExpr = scope(Reason, SubGoal)

It appears that this goal feature propagates outside promise_pure scopes.
I realise this behaviour follows what is in the reference manual, but is
this really what we want?

I think that a goal which is explicitly promised pure should be able to
be optimised away even if it contains trace goals, in the same way that
a pure call can be optimised away even if there are trace goals in its
definition.

Any comments?

Cheers,
Mark.

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