This library collects utilities to reason about terms commonly needed
for reasoning about Prolog code. Note that many related facilities can
be found in the core as well as other libraries:
- comma_list(?CommaList, ?List)
- semicolon_list(?SemicolonList, ?List)
- True if CommaList is a nested term over the ','/2 (';'/2) functor
and List is a list expressing the elements of the conjunction. The
predicate is deterministic if at least CommaList or List is
sufficiently instantiated. If both are partial structures it
enumerates ever growing conjunctions and lists. CommaList may be
left or right associative on input. When generated, the CommaList is
always right associative.
This predicate is typically used to reason about Prolog conjunctions
(disjunctions) as many operations are easier on lists than on binary
trees over some operator.
- mkconj(A, B, Conj) is det
- mkdisj(A, B, Disj) is det
- Create a conjunction or disjunction from two terms. Reduces on
true (mkconj/2) and
false (mkdisj/2). Note that a
encountered in a conjunction does not cause the conjunction to
false, i.e. semantics under side effects are preserved.
; operators are of type
xfy, i.e. right
associative. These predicates preserve this grouping. For example,
?- mkconj((a,b), c, Conj)
Conj = (a,b,c)
- is_predicate_indicator(@Term) is semidet
- True when Term is a predicate indicator
- pi_head(?PredicateIndicator, ?Goal) is det
- Translate between a PredicateIndicator and a Goal term. The terms
may have a module qualification.
- head_name_arity(?Goal, ?Name, ?Arity) is det
- Similar to functor/3, but deals with SWI-Prolog's zero-argument
callable terms and avoids creating a non-callable term if Name is
not an atom and Arity is zero.
- most_general_goal(+Goal, -General) is det
- General is the most general version of Goal. Goal can be qualified.
- See also
- - is_most_general_term/1.
- extend_goal(:Goal0, +Extra, -Goal) is det
- Extend the possibly qualified Goal0 with additional arguments from
Extra. If Goal0 is insufficiantly instantiated (i.e., a variable), a
call(Goal0, ...) is returned.
- predicate_label(++PI, -Label) is det
- Create a human-readable label for the given predicate indicator.
This notably hides the module qualification from
user and built-in
predicates. This predicate is intended for reporting predicate
information to the user, for example in the profiler.
First PI is converted to a head and the hook
prolog_predicate_name/2 is tried.
- predicate_sort_key(+PI, -Key) is det
- Key is the (module-free) name of the predicate for sorting purposes.
- True if Goal is a compiled Prolog control structure. The difference
between control structures and meta-predicates is rather unclear.
The constructs below are recognised by the compiler and cannot be
redefined. Note that (if->then;else) is recognised as
- body_term_calls(:BodyTerm, -Goal) is nondet
- True when BodyTerm calls Goal. This predicate looks into control
structures as well as meta predicates based on predicate_property/2.
When a variable is called, this is normally returned in Goal.
Currently if a variable is called with additional arguments, e.g.,
call(Var, a1), this call is reported as
The following predicates are exported, but not or incorrectly documented.
- semicolon_list(Arg1, Arg2)
- mkdisj(Arg1, Arg2, Arg3)