SWI-Prolog -- macro

Documentation
- Reference manual
  - The SWI-Prolog library
    - library(macros): Macro expansion
      - Predicates
        
        include_macros/3
        
        expand_macros/5
        
        macro_position/1
- Packages

Availability::- use_module(library(macros)).(can be autoloaded)

[det]macro_position(-Position)

True when Position is the position of the macro. Position is a term File:Line:LinePos. If File is unknown it is unified with -. If Line and/or LinePos are unknown they are unified with 0. This predicate can be used in the body of a macro definition to provide the source location. The example below defines #pp(Var) to print a variable together with the variable name and source location.

#define(pp(Var), print_message(debug, dump_var(Pos, Name, Var))) :-
    (   var_property(Var, name(Name))
    ->  true
    ;   Name = 'Var'
    ),
    macro_position(Pos).

:- multifile prolog:message//1.
prolog:message(dump_var(Pos,Name,Var)) -->
    [ url(Pos), ': ',
      ansi([fg(magenta),bold], '~w', [Name]), ' = ',
      ansi(code, '~p', [Var])
    ].