51 prolog

     %--------------------------------------------------%
     % vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
     %--------------------------------------------------%
     % Copyright (C) 1997-2003, 2005-2006, 2012 The University of Melbourne.
     % This file may only be copied under the terms of the GNU Library General
     % Public License - see the file COPYING.LIB in the Mercury distribution.
     %--------------------------------------------------%
     %
     % File: prolog.m.
     % Main author: fjh.
     % Stability: high.
     %
     % This file contains predicates that are intended to help people
     % porting Prolog programs, or writing programs in the intersection
     % of Mercury and Prolog.
     %
     %--------------------------------------------------%
     %--------------------------------------------------%
     
     :- module prolog.
     :- interface.
     
     :- import_module list.
     :- import_module pair.
     :- import_module univ.
     
     %--------------------------------------------------%
     %
     % Prolog arithmetic operators
     %
     
     :- pred T =:= T.            % In Mercury, just use =
     :- mode in =:= in is semidet.
     
     :- pred T =\= T.            % In Mercury, just use \=
     :- mode in =\= in is semidet.
     
     /*******
     is/2 is currently defined in int.m, for historical reasons.
     
     :- pred is(T, T) is det.        % In Mercury, just use =
     :- mode is(uo, di) is det.
     :- mode is(out, in) is det.
     ******/
     
     %--------------------------------------------------%
     %
     % Prolog term comparison operators
     %
     
     :- pred T == T.             % In Mercury, just use =
     :- mode in == in is semidet.
     
     :- pred T \== T.            % In Mercury, just use \=
     :- mode in \== in is semidet.
     
     % Prolog's so-called "univ" operator, `=..'.
     % Note: this is not related to Mercury's "univ" type!
     % In Mercury, use `deconstruct.deconstruct' instead.
     
     :- pred T =.. univ_result.
     :- mode in =.. out is det.
         %
         % Note that the Mercury =.. is a bit different to the Prolog
         % one.  We could make it slightly more similar by overloading '.'/2,
         % but that would cause ambiguities that might prevent type
         % inference in a lot of cases.
         %
     % :- type univ_result ---> '.'(string, list(univ)).
     :- type univ_result == pair(string, list(univ)).
     
         % arg/3.
         % In Mercury, use arg/4 (defined in module deconstruct) instead:
         %
         %   arg(ArgNum, Term, Data) :-
         %       deconstruct.arg(Term, canonicalize, ArgNum - 1, Data).
         %
     :- pred arg(int::in, T::in, univ::out) is semidet.
     
         % det_arg/3: like arg/3, but calls error/1 rather than failing
         % if the index is out of range.
         %
     :- pred det_arg(int::in, T::in, univ::out) is det.
     
     %--------------------------------------------------%
     %--------------------------------------------------%