Definite Clause Translation Grammar Translator
                      Contributed by Jocelyn Ireson-Paine
                    Shelved on the 21st of July 1990


This entry comes as three files:
    DCTG.PRE    - this file.
    DCTG.PL     - the translator itself.
    DCTGTEST.PL - a test program.


Definite Clause Translation Grammars are described in chapter 9 of
"Logic Grammars", by H.Abramson and V.Dahl (Springer 1989). They were
devised by Abramson to overcome the defects of Definite Clause Grammars,
in which syntax and semantics are often mixed in a non-modular fashion.
They avoid also the proliferation of unnamed arguments that aflicts
Definite Clause Grammars.

In a DCTG, the syntax and semantics are separated. Each rule contains
first a syntactic part, and then an optional semantics, written as one
or more clauses. See DCTGTEST.PL for an example, and "Logic Grammars"
for more details.

Most of the code in this entry comes from Appendix II of "Logic
Grammars". I have made a few changes:

1.  I use the operator && to separate semantic clauses. Abramson used
    comma, and so needed an extra layer of brackets to separate them.

2.  The form
        Attribute from X
    is an abbreviation for
        Attribute(V) ::- X^^Attribute(V)

3.  There is a predicate "dctg_reconsult" for loading grammars from
    file.                   


To run the software, consult DCTG.PL, use it to load the grammar in
DCTGTEST.PL, and then call 'go' for a demonstration:
    ?- [ -'dctg.pl' ].
    dctg_reconsult( 'dctgtest.pl' ).
    go.



CHECKED ON EDINBURGH-COMPATIBLE (POPLOG) PROLOG : yes.


PORTABILITY : No problems.


INTERNAL DOCUMENTATION :

    Only dctg_reconsult is documented in the code. See "Logic Grammars"
    for the meaning of the other predicates, and the theory.