[mercury-users] Assoc-List: keys ground & values unique

[Kral Stefan]

Hi Everyone.

I need to do a variant of assoc_list that can hold something unique 
as the value. Of course, I tried anything promising (to me), but
it didn't quite work out.

So, assuming a data-type like
	:- type gmpkv ---> index_content(int, gmpint).
and a predicate like 
	:- pred assoclist_fetch(int, gmpint, list(gmpkv), list(gmpkv)).
which does a lookup of the 1st arg in the 3rd, returning the 2nd and
the 4th (upon success). The returned assoclist does not contain the
key-value "pair" anymore. (I wanted to use "real" pairs at first. But 
as two args are integers, that did not appear to be such a good idea...)

What should the mode declaration look like?

My first guess was
	:- mode assoclist_fetch(in, uo, di, uo) is semidet.
the second one
	:- mode assoclist_fetch(in, uo, di(list(unique)),
					free >> unique(list(unique))) 
							is semidet.
then I tried all kinds of variations that describe the instantiatedness
tree in more (and more) details, yet I did not hit the right one yet.

It the problem solely on my side or it is also on the current status 
of the implementation of unique modes within the Mercury compiler?

(My next step will be using unsafe_promise_unique at appropriate 
places, hoping this will not kick correctness out of the window.)

I would appreciate any hint on that issue.

Best regards,
Stefan.

-- 
Stefan Kral            http://www.complang.tuwien.ac.at/skral/

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