Logtalk reference manual
Control construct: {}/1
Contents > Reference Manual > Control Constructs > {}/1

## {}/1

#### Description

    {Term}
    {Goal}

This control construct allows the programmer to bypass the Logtalk compiler. It can be used to wrap a source file term (either a clause or a directive) to bypass the term-expansion mechanism. Similarly, it can be used to wrap a goal to bypass the goal-expansion mechanism. When used to wrap a goal, it is opaque to cuts and the argument is called within the context of the pseudo-object user. It is also possible to use `{Closure}` as the first argument of `call/2-N` calls. In this case, `Closure` will be extended with the remaining arguments of the `call/2-N` call in order to construct a goal that will be called within the context of `user`. It can also be used as a message to any object. This is useful when the message is e.g. a conjunction of messages, some of which being calls to Prolog built-in predicates.

This control construct may also be used in place of an object identifier when sending a message. In this case, the result of proving its argument as a goal (within the context of the pseudo-object `user`) is used as an object identifier in the message sending call. This feature is mainly used with parametric objects when the their identifiers correspond to predicates defined in `user`.

#### Template and modes

    {+callable}

#### Errors

Term or Goal is a variable:
  `instantiation_error`
Term is neither a variable nor a callable term:
  `type_error(callable, Term)`
Goal is neither a variable nor a callable term:
  `type_error(callable, Goal)`

#### Examples

    {:- load_foreign_resource(file)}.

    N1/D1 < N2/D2 :-
        {N1*D2 < N2*D1}.

    call_in_user(F, X, Y, Z) :-
        call({F}, X, Y, Z).

    | ?- {circle(Id, Radius, Color)}::area(Area).
    ...

    | ?- logtalk::{write('Hello world!'), nl}.
    Hello world!
    yes