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).
[nondet]phrase_from_file(:Grammar,
+File)