[m-dev.] for review: fix existential types bug

[Fergus Henderson]

On 25-Oct-1999, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > 
> > On 25-Oct-1999, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > > 
> > > compiler/polymorphism.m:
> > > 	Add the type-info variables added for the existential
> > > 	type variables of a constructor to the non-locals of
> > > 	the construction.
> > 
> > Hmm... why doesn't the call to implicitly_quantify_goal
> > in polymorphism__fixup_quantification fix that?
> > (polymorphism__fixup_quantification is called from
> > polymorphism__process_clause.)
> 
> implicitly_quantify_goal is only called from
> polymorphism__fixup_quantification if the predicate being
> processed has type variables in the argument types.
> This does not check whether called predicates, functions
> or constructors have type variables in their argument types.

That used to be the case a while back, but since my changes
to add existential types, it should not be true now.
The comment on polymorphism__fixup_quantification says

% If the pred we are processing is a polymorphic predicate,
% or contains polymorphically-typed goals, ...
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

and the code checks whether the type_info_map in the poly_info
is empty.  If there are any polymorphically typed variables
in the body of the predicate, then the type_info_map should
be non-empty.

> > > +		goal_info_get_nonlocals(GoalInfo0, NonLocals0),
> > > +		set__insert_list(NonLocals0, ExtraVars, NonLocals),
> > > +		goal_info_set_nonlocals(GoalInfo0, NonLocals, GoalInfo),
> > >  		Unify = unify(X0, functor(ConsId, ArgVars), Mode0,
> > > -				Unification0, UnifyContext) - GoalInfo0,
> > > +				Unification0, UnifyContext) - GoalInfo,
> > >  		list__append(ExtraGoals, [Unify], GoalList),
> > >  		conj_list_to_goal(GoalList, GoalInfo0, Goal)
> > 
> > Shouldn't that last occurrence of `GoalInfo0' be `GoalInfo'?
> 
> No, because the extra type-infos are local to that conjunction.

Are you sure?
What about for e.g.

	:- type f ---> some [T] foo(T).

	:- pred p(bool, f, io__state, io__state).
	:- mode p(in, in, di, uo) is det.
	p(Flag, U) -->
		(if { Flag = yes, U = foo(X) } then
			io__print(X)
		else
			[]
		).

After polymorphism this will be

	p(Flag, U) -->
		(if { Flag = yes, U = foo(TypeInfo, X) } then
			io__print(TypeInfo, X)
		else
			[]
		).

and the scope of TypeInfo is not local to the conjunction.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.
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