Arithmetic can be divided into some special purpose integer
predicates and a series of general predicates for floating point and
integer arithmetic as appropriate. The integer predicates are as
``logical'' as possible. Their usage is recommended whenever applicable,
resulting in faster and more ``logical'' programs.
The general arithmetic predicates are optionally compiled now (see
set_prolog_flag/2
and the -O command line option). Compiled arithmetic
reduces global stack requirements and improves performance.
Unfortunately compiled arithmetic cannot be traced, which is why it is
optional.
The general arithmetic predicates all handle expressions.
An expression is either a simple number or a function. The
arguments of a function are expressions. The functions are described in
section 4.27.
- between(+Low, +High,
?Value)
-
Low and High are integers, High >=Low.
If
Value is an integer, Low =<Value
=<High. When Value is a variable it is
successively bound to all integers between Low and High.
- succ(?Int1, ?Int2)
-
Succeeds 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. (38)
- plus(?Int1, ?Int2, ?Int3)
-
Succeeds if Int3 = Int1 + Int2.
At least two of the three arguments must be instantiated to integers.
- +Expr1 > +Expr2
-
Succeeds when expression Expr1 evaluates to a larger number
than Expr2.
- +Expr1 < +Expr2
-
Succeeds when expression Expr1 evaluates to a smaller number
than Expr2.
- +Expr1 =< +Expr2
-
Succeeds when expression Expr1 evaluates to a smaller or
equal number to Expr2.
- +Expr1 >= +Expr2
-
Succeeds when expression Expr1 evaluates to a larger or equal
number to Expr2.
- +Expr1 =\= +Expr2
-
Succeeds when expression Expr1 evaluates to a number
non-equal to
Expr2.
- +Expr1 =:= +Expr2
-
Succeeds when expression Expr1 evaluates to a number equal to
Expr2.
- -Number is +Expr
-
Succeeds when Number has successfully been unified with the
number
Expr evaluates to. If Expr evaluates to a float
that can be represented using an integer (i.e, the value is integer and
within the range that can be described by Prolog's integer
representation), Expr is unified with the integer value.
Note that normally, is/2
will be used with unbound left operand. If equality is to be tested,
=:=/2 should be used. For example:
?- 1.0 is sin(pi/2). | Fails!.
sin(pi/2) evaluates to 1.0, but is/2
will represent this as the integer 1, after which unify will fail. |
?- 1.0 is float(sin(pi/2)). | Succeeds,
as the float/1
function forces the result to be float. |
?- 1.0 =:= sin(pi/2). | Succeeds
as expected. |