arithpreds.yap

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/*************************************************************************
*                                    *
*    YAP Prolog                              *
*                                    *
*   Yap Prolog was developed at NCCUP - Universidade do Porto    *
*                                    *
  * Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997     *
*                                    *
**************************************************************************
*                                    *
* File:     arithpreds.yap                       *
* Last rev:                              *
* mods:                                  *
* comments: arithmetical predicates              *
*                                    *
*************************************************************************/
 
/**
  @file arithpreds.yap
 
  @addtogroup arithmetic Arithmetic Predicates and Functions
 
@{
 
*/
   
:- plus/3succ/2system_module(arithmetic_predicates, [
        ,
        ], []).
 
:- '$do_error'/2use_system_module( '$_errors', []).
 
/** @pred succ(? _Int1_:int, ? _Int2_:int) is det
  *
 
  True if  _Int2_ =  _Int1_ + 1 and  _Int1_ >= 0. At least
  one of the arguments must be instantiated to a natural number. This
  predicate raises the domain-error not_less_than_zero if called with
  a negative integer. E.g. `succ(X, 0)` fails silently and `succ(X, -1)`
  raises a domain-error. The behaviour to deal with natural numbers
  only was defined by Richard O'Keefe to support the common
  count-down-to-zero in a natural way.
 
  */
 
% M and N nonnegative integers, N is the successor of M
succ(M,N) :-
    (
     var(M)
    ->
     (
      integer(N),
      N > 0
     ->
      '$plus'(N,-1,M)
     ;
      '$succ_error'(M,N)
     )
    ;
     integer(M),
     M >= 0
    ->
     (
      var(N)
     ->
     '$plus'(M,1,N)
     ;
      integer(N),
      N > 0
     ->
     '$plus'(M,1,N)
     ;
      '$succ_error'(M,N)
     )
    ;
     '$succ_error'(M,N)
    ).
 
'$succ_error'(M,N) :-
    var(M),
    var(N), var,
    '$do_error'(instantiation_error,succ(M,N)).
'$succ_error'(M,N) :-
    nonvar(M),
    \+ integer(M),
    '$do_error'(type_error(integer, M),succ(M,N)).
'$succ_error'(M,N) :-
    nonvar(M),
    M < 0,
    '$do_error'(domain_error(not_less_than_zero, M),succ(M,N)).
'$succ_error'(M,N) :-
    nonvar(N),
    \+ integer(N),
    '$do_error'(type_error(integer, N),succ(M,N)).
'$succ_error'(M,N) :-
    nonvar(N),
    N < 0,
    '$do_error'(domain_error(not_less_than_zero, N),succ(M,N)).
 
/** @pred plus(? _Int1_:int, ? _Int2_:int, ? _Int3_:int) is det
 
  True if  _Int3_ =  _Int1_ +  _Int2_. At least two of the
  three arguments must be instantiated to integers.
 
  */
 
plus(X, Y, Z) :-
       (
        var(X)
       ->
        (
         integer(Y), integer(Z)
        ->
         '$minus'(Z,Y,X)
        ;
         '$plus_error'(X,Y,Z)
        )
       ;
        integer(X)
       ->
        (
         var(Y)
        ->
         (
          integer(Z)
         ->
          '$minus'(Z,X,Y)
         ;
         '$plus_error'(X,Y,Z)
         )
        ;
         integer(Y)
        ->
         (
          integer(Z)
         ->
          '$minus'(Z,Y,X)
         ;
          var(Z)
         ->
          '$plus'(X,Y,Z)
         ;
          '$plus_error'(X,Y,Z)
         )
        ;
         '$plus_error'(X,Y,Z)
        )
       ;
        '$plus_error'(X,Y,Z)
       ).
 
'$plus_error'(X,Y,Z) :-
       nonvar(X),
       \+ integer(X),
       '$do_error'(type_error(integer, X),plus(X,Y,Z)).
'$plus_error'(X,Y,Z) :-
       nonvar(Y),
       \+ integer(Y),
       '$do_error'(type_error(integer, Y),plus(X,Y,Z)).
'$plus_error'(X,Y,Z) :-
       nonvar(Z),
       \+ integer(Z),
       '$do_error'(type_error(integer, Z),plus(X,Y,Z)).
'$plus_error'(X,Y,Z) :-
       '$do_error'(instantiation_error,plus(X,Y,Z)).
 
%% @}
-