Process the content of File using the DCG rule Grammar. The
space usage of this mechanism depends on the length of the not
committed part of Grammar. Committed parts of the temporary list
are reclaimed by the garbage collector, while the list is
extended on demand due to unification of the attributed tail
variable. Below is an example that counts the number of times a
string appears in a file. The library dcg/basics provides
string//1 matching an arbitrary string and remainder//1 which
matches the remainder of the input without parsing.
:- use_module(library(dcg/basics)).
file_contains(File, Pattern) :-
phrase_from_file(match(Pattern), File).
match(Pattern) -->
string(_),
string(Pattern),
remainder(_).
match_count(File, Pattern, Count) :-
aggregate_all(count, file_contains(File, Pattern), Count).
This can be called as (note that the pattern must be a string
(code list)):
?- match_count('pure_input.pl', `file`, Count).