parameter/2

Description

parameter(Number, Term)

Used in parametric objects (and parametric categories), this private method provides runtime access to parameter values by using the argument number in the object (or category) identifier. This predicate is implemented as a unification between its second argument and the corresponding implicit execution-context argument in the predicate containing the call. For parametric objects, this unification occurs at the clause head, not at the clause body. See also this/1.

Template and modes

parameter(+integer, ?term)

Errors

Number is a variable:

instantiation_error

Number is neither a variable nor an integer value:

type_error(integer, Number)

Object identifier is not a compound term:

type_error(compound, Object)

Number is a negative integer value:

domain_error(not_less_than_zero, Number)

Examples

:- object(box(_Color, _Weight)).

    ...
    
    color(Color) :-              % this clause is translated into a fact
        parameter(1, Color).     % upon compilation 

    heavy :-
        parameter(2, Weight),    % after compilation, the >/2 call will be
        Weight > 10.             % the first condition on the clause body

    ...