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yap-6.3/pl/arithpreds.yap

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2014-04-21 11:14:18 +01:00
/*************************************************************************
* *
* 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_preds
@{
*/
:- system_module(arithmetic_predicates, [
plus/3,
succ/2], []).
:- use_system_module( '$_errors', ['$do_error'/2]).
/** 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)
).
'$succ_error'(M,N) :-
var(M),
var(N), !,
'$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)).
/** 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)).