[Faddey]

Can anyone explain the difference between the predicates (or notation) toBinary(Term) = Binary and ::toBinary(Term) = Binary.

[Martin Meyer]

The Language Reference teaches:

Visual Prolog contains an embedded hidden class, which provides declarations and implementations to all built-in constants, domains, and predicates.
...
Each compilation unit implicitly contains the declaration of this embedded hidden class. To disambiguate from other entities with the same name you can use "::" before names of built-in items.

An example to demonstrate the disambiguation of built-in predicate toBinary from a user-defined predicate with same name:

Code: Select all

class predicates
    toBinary : (Term) -> binary Ones.
clauses
    toBinary(_) = $[01, 01, 01, 01].
 
constants
    zero : integer = 0.
 
clauses
    run() :-
        BuiltIn = ::toBinary(zero),
        UserDefined = toBinary(zero),
        stdIo::write(BuiltIn, '\n'),
        stdIo::write(UserDefined, '\n').

The example outputs:

Code: Select all

$[00,00,00,00]
$[01,01,01,01]

[Faddey]

Thank you very much Martin.