add motivation and comments about library(pio) predicates
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ Pure I/O
+ ========
+
+ Our goal is to encourage the use of definite clause grammars (DCGs)
+ for describing strings. The predicates phrase_from_file/[2,3],
+ phrase_to_file/2 and phrase_to_stream/2 let us apply DCGs transparently
+ to files and streams, and therefore decouple side-effects from
+ declarative descriptions.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
:- module(pio, [phrase_from_file/2,
phrase_from_file/3,
phrase_to_file/2,
:- meta_predicate(phrase_to_file(2, ?)).
:- meta_predicate(phrase_to_stream(2, ?)).
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ phrase_from_file(GRBody, File)
+
+ True if grammar rule body GRBody covers the contents of File,
+ represented as a list of characters.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
phrase_from_file(NT, File) :-
phrase_from_file(NT, File, []).
