Module dcgs
:- use_module(library(dcgs)).Support for Definite Clause Grammars.
A Prolog definite clause grammar (DCG) describes a sequence. Operationally, DCGs can be used to parse, generate, complete and check sequences manifested as lists.
Check The Power of Prolog chapter on DCGs to learn more about them.
phrase(+Body, ?Ls).
True iff Body describes the list Ls. Body must be a DCG body. It is equivalent to phrase(Body, Ls, []).
Examples:
as --> [].
as --> [a], as.
?- phrase(as, Ls).
Ls = []
; Ls = "a"
; Ls = "aa"
; Ls = "aaa"
; ... .
?- phrase(as, "aaa").
true.phrase(+Body, ?Ls, ?Ls0).
True iff Body describes part of the list Ls and the rest of Ls is Ls0.
Example:
?- phrase(seq(X), "aaa", Y).
X = [], Y = "aaa"
; X = "a", Y = "aa"
; X = "aa", Y = "a"
; X = "aaa", Y = [].seq(Seq)//
Describes a sequence
seqq(SeqOfSeqs)//
Describes a sequence of sequences
...//
Describes an arbitrary number of elements