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# viewable(?ViewableName)

Test/enumerate names of all existent viewables.

ViewableName
  Atom or string: name of a viewable.

## Description

NOTE:When there are no registered visualisation clients, this predicate fails with all arguments, and has no effect.

If ViewableName is instantiated, tests whether ViewableName is the name of an existent viewable. If not, ViewableName is successively instantiated to the names of all existent viewables.

### Fail Conditions

Fails if ViewableName is not / cannot be instantiated to the name of an existent viewable.

### Resatisfiable

yes

### Exceptions

(4) instantiation fault
  ViewableName is not an atom, string or free variable

## Examples

    [Assuming that at least one visualisation client is registered]

         Success:

         viewable_create(my_viewable, [X,Y,Z], array([fixed], any)),
           viewable(my_viewable).

         Failure:

         viewable(non_viewable)

         Exception raised:

         viewable(123).
         [raises error 4].

## See Also

viewable_create / 2, viewable_create / 3