add subsumes_term/2

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "scryer-prolog"
-version = "0.8.71"
+version = "0.8.72"
 authors = ["Mark Thom <markjordanthom@gmail.com>"]
 repository = "https://github.com/mthom/scryer-prolog"
 description = "A modern Prolog implementation written mostly in Rust."

README.md

@@ -223,6 +223,7 @@ The following predicates are built-in to Scryer.
 * `setup_call_cleanup/3`
 * `sort/2`
 * `string/1`
+* `subsumes_term/2`
 * `term_expansion/2`
 * `term_variables/2`
 * `throw/1`

src/prolog/lib/builtins.pl

@@ -17,8 +17,8 @@
 	expand_goal/2, expand_term/2, false/0, findall/3, findall/4,
 	get_char/1, halt/0, number_chars/2, once/1, op/3, read_term/2,
 	repeat/0, retract/1, set_prolog_flag/2, setof/3,
-	term_variables/2, throw/1, true/0, write/1, write_canonical/1,
-	write_term/2, writeq/1]).
+	subsumes_term/2, term_variables/2, throw/1, true/0, write/1,
+	write_canonical/1, write_term/2, writeq/1]).
 
 % module resolution operator.
 :- op(600, xfy, :).
@@ -815,3 +815,11 @@ number_chars(N, Chs) :-
       '$number_to_chars'(N, Chsx),
       Chsx = Chs
     ).
+
+subsumes_term(General, Specific) :-
+   \+ \+ (
+      term_variables(Specific, SVs1),
+      General = Specific,
+      term_variables(SVs1, SVs2),
+      SVs1 == SVs2
+   ).