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Asked: 2026-05-27T21:44:15+00:00

I am looking for extensional DCG test cases. Means test cases that check the

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I am looking for extensional DCG test cases. Means
test cases that check the right functioning of a DCG
processor in terms of the behaviour of the resulting
converted rules, and not in terms of its desugaring
capability.

I think I saw some such test cases once on the net.
But I lost track of them. Now I only find the following
test cases:

http://www.sju.edu/~jhodgson/wg17/Drafts/DCGs/test_cases
(Same here: http://www.sju.edu/~jhodgson/wg17/dcgs.pdf)

But they are only perpherically and intensional, i.e.
they test whether desugaring, the conversion, succeeds
or gives an error. They even don’t show what the conversion
result should be, which doesn’t bother me since I am
anyway looking for extensional DCG test cases.

Any pointers welcome.

Bye

P.S:
This one shows the conversion, but it is still intensional
and not extensional:
http://www.sju.edu/~jhodgson/wg17/GRIND.TXT
And it has for example:

expand(( a(4)-->[98] ),
   (a(4, S0, S1):- 'C'( S0,98, S1))).
expand(( a(28)--> \+b,c ),
   (a(28,_608,_609):-(b(_608,_619)->fail;_617=_608),c(_617,_609))).

But many Prolog systems use a different approach for terminals,
negation, etc.. in DCG. So an extensional test suite would
be more handy.

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1 Answer

  1. Editorial Team

    Just completed a couple of extensional DCG test cases. The test cases
    do cover the following:

    Predicate . / 4: Terminals
    Predicate (–>) / 2: Non-Terminals
    Predicate (,) / 4: Conjunction
    Predicate (;) / 4: Disjunction
    Predicate (->) / 4: Implication
    Predicate (+) / 3: Negatio as Failure
    Predicate ! / 2: Cut
    Predicate {} / 3: Auxiliary Conditions

    Some of the test cases check for steadfastness. The total number
    of test cases is: 56.

    The test cases do not cover push back and meta calls inside DCG.
    The test cases make use of @/3 here and then, so that when using listing/[0,1]
    the original DCG code is seen and not the expansion of it. The @/3
    is defined as follows:

    @(X) --> X.

    The test cases are inspired by:
    Moura, P. ed. (2010): Prolog, Part 3: Definite Clause Grammar Rules, Draft, ISO/IEC DTR 13211 3:2006, April 1, 2010

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