preliminary support for a subset of quads introduced by @UWN

[triska]

This lets us embed toplevel interactions in Prolog programs. Embedded toplevel interactions are currently ignored.

Example:

:- use_module(library(lists)).

?- member(X, "abc").
   X = a
;  X = b
;  X = c.

[hurufu]

Isn't it better to use term expansion mechanism to replace them with nothing? The ability to selectively remove terms during compilation was already asked here.

[bakaq]

I was going to ask exactly for this feature actually! This works specially nice with warnings as comments, and I think it may also make the experience with ediprolog and similar systems much nicer (though I don't use ediprolog so this is a guess)!

[triska]

Yes this would be ideal! The issue here is that one or more answer descriptions can follow a query, so this goes beyond a single term. A description that is not preceded by a query should yield an error or be treated as a regular fact as the case might be.

[bakaq]

The issue here is that one or more answer descriptions can follow a query [...]

Oh, so it's support also for things like this and not only actual outputs of queries in the toplevel?

?- example.
   X = 1, unexpected.
   X = 2, expected.

This notation that you seem to use is the only place I can think where more than one term comes after a query. Also, why the name "quads"?

[UWN]

X = 2, expected.

Here, expected is not needed, because X = 2. just states this alone. Only unexpected is needed to document that that leaf answer is not expected at that very moment. In this manner the same quad can be used as bug report and test case.

Also, why the name "quads"?

Queries using answer descriptions. So this is about either plain answers, as above, or some descriptions thereof. Think of ... . produced by the top level.

[UWN]

@bakaq, see the Prolog prologue for more quads.