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