[m-dev.] for review: add exception__try_store

[Fergus Henderson]

On 22-Feb-2001, Mark Anthony BROWN <dougl at cs.mu.OZ.AU> wrote:
> > -:- pred get_determinism_2(pred(T, io__state, io__state), determinism).
> > +:- pred get_determinism_2(pred(T, S, S), determinism).
> >  :- mode get_determinism_2(pred(out, di, uo) is det,      out(bound(det)))
> >  	is cc_multi.
> >  :- mode get_determinism_2(pred(out, di, uo) is cc_multi, out(bound(cc_multi)))
> 
> The spacing of the mode declarations was such that the mode of the second
> argument lined up with the type, to make it easier to read.  This is no
> longer the case, so it would be good if you could either fix or remove the
> extra space.

I'll add extra spaces to make it line up.

> > +% In other words, with a naive implementation of `try_store',
> > +% the following program could print out 
> > +% 
> > +% 	Result = exception(initial)
> > +% 	Result = exception(updated)
> 
> That's not exactly what could be printed out, although it is clear what
> you mean.

I'll fix that (it should be `exception(univ_cons(initial))' and likewise
for `updated').

> > +main -->
> > +	{ store__new(Store0) },
> > +	{ store__new_ref(mklist("initial"), Key, Store0, Store1) },
> > +	{ store__arg_ref(Key, 0, SubKey, Store1, Store2) },
> > +	{ exception__try_store(tricky(Key), Result, Store2, Store3) },
> > +	print("Result = "), print(Result), nl,
> > +	{ store__set_ref_value(SubKey, "updated", Store3, Store) },
> > +	print("Result = "), print(Result), nl,
> > +	{ store__extract_ref_value(Store, Key, Val) },
> > +	print("Val = "), print(Val), nl.
> 
> The call to set_ref_value might be reordered after the following calls
> to print, which means that this test case could pass even if try_store
> does not do the right thing.

Sure.  But in general test cases can only ever show the presence of bugs,
not their absence.  In other words, I think it's OK as is ;-)

If you have a particular suggestion about how it could be improved
I'll certainly consider it.

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