compile_term(+Clause)

+Clause

A valid Prolog clause, or list of clauses.

Description

If Clause is a list, the list elements are interpreted as consecutive clauses. Otherwise, Clause will be taken as a single clause. Each clause may be a fact or a rule.

This predicate works almost as if all the clauses in the list were written into a file and this file was then compiled using compile/1. It does however not perform any inline expansion on the goals in the clause bodies. To do this, explicit preprocessing of the clauses is required (e.g. using expand_goal/2). This may change in a future release.

The difference between compile_term/1 and assert/1 is that the predicates for which clauses are compiled are not necessarily dynamic with compile_term/1, unless explicitly declared as such. Therefore clauses compiled with compile_term/1 usually replace the existing ones for the same predicate, moreover their source form is not available. Therefore, it can be used instead of assert/1 if the properties of dynamic procedures are not required.

Unlike compiling a file, when an event occurs which is not just a warning, the following clauses are not compiled, the compilation is aborted.

See compile/1 for a more complete list of exceptions that can occur during compilation.

Fail Conditions

Resatisfiable

Exceptions

(4) instantiation fault

Clause is a partial list.

(5) type error

Clause is a list whose tail is neither nil nor a variable.

(82) trying to access a locked module

The module in which the clauses should be compiled is locked.

(94) trying to redefine an existing imported procedure

There is already am imported predicate of the same name.

(130) syntax error: illegal head

The head of a clause is not an atom or a compound term.

(131) syntax error: illegal goal

A subgoal in the body of a clause is not an atom, a compound term or a variable.

(134) procedure clauses are not consecutive

The clauses of a procedure are not consecutive.

(136) trying to redefine a built-in predicate

Trying to redefine a built-in predicate without having declared it.

(137) trying to redefine a procedure with another type

A procedure which was previously referenced as built-in or external is now defined as a regular one, or vice versa.

(143) compiled query failed

One of the clauses was a query and it failed.

Examples

Success:
   % several facts for different predicates
   ?- compile_term([p(a), p(b), q(1), r("abc")]).

   % a single clause
   ?- compile_term(p(X) :- q(X)).

   % two clauses for the same predicate
   ?- compile_term([p([]), (p([X|Xs]) :- writeln(X), p(Xs))]).

   % a declaration and two clauses
   ?- compile_term([(:- export p/1), p(a), p(b)]).



   % Compile_term/1 can be used for conditional compilation:
   :- (exists('/usr/ucb') -> S = bsd; S = sysV),
      compile_term(os(S)).

   % Even a whole procedure can be conditionally compiled:
   :- os(bsd) ->
    compile_term([
        (pred1(X) :- pred2(X), pred3(X)),
        (pred1(Y) :- ...           )]).


Error:

   compile_term([p|X]).          (Error 4).
   compile_term([a|b]).          (Error 5).
   compile_term([[a]]).          (Error 94).
   compile_term([(p :- write(a)), write(b)]).      (Error 94).
   compile_term("a").          (Error 130).
   compile_term(["a" :- b]).   (Error 130).
   compile_term([p(X) :- 1]).    (Error 131).
   compile_term([a, b, a]).      (Error 134).
   compile_term(!).              (Error 135).
   compile_term(:- var(a)).      (Error 143).

See Also