1.109 class number

A number object represents an integer just like the primitive type int. Numbers are more costly, but allow for some operations such as comparison or addition.

Instances of class number are commonly used to implement counters:

count_instances(Device, Class, Instances) :-
        new(I, number(0)),
        send(Device, for_all, @default,
                 if(message(@arg1, instance_of, Class),
                    message(I, plus, 1))),
        get(I, value, Instances),
        send(I, done).

See also class real.

See also

- class binary_expression
- pce<-max_integer

1.109.1 Instance variables

number-value: alien:long

Represented value. This is an int and thus limited to the range

`@pce <-min_integer` .. `@pce <-min_integer`

1.109.2 Send methods

number ->minus: int|number

Subtract argument from value.

number ->plus: int|number

Add argument to value.

number ->times: int|number

Multiply value by argument.

number ->divide: int|number

Basic arithmetic operations. Note that arithmetic may also be performed by the function classes /, +, - and *. Numbers are useful as accumulators (see the various examples in this class). Functions are more convenient in expressions.

number ->equal: int|number|real

Succeeds if the argument represents the same value. Note that PCE type conversion converts real objects, number objects and text to ints and thus all the following succeed:

?- send(number(1), equal, 1).
?- send(number(1), equal, 1.0).
?- send(number(1), equal, number(1)).
?- send(number(1), equal, '1').

number ->larger_equal: int|number|real

Test if larger-or-equal than argument.

number ->less_equal: int|number|real

Test if less-or-equal than argument.

number ->not_equal: int|number|real

Test if not-equal to argument.

number ->smaller: int|number|real

Test if less than argument.

number ->larger: int|number|real

Compare the receiver to the argument by value. The receiver is tested to be {number->larger, number->smaller, ...} than the argument.

number ->minimum: int|number

Set value to largest of current and argument.

number ->maximum: int|number

Set number<-value to the {number->maximum, number->minimum} of the current number<-value and the argument. Useful in may computations. Suppose Chain is a chain holding string and we which to know the widest string given the font Font:

width_of_strings(Chain, Font, Width) :-
        new(W, number(0)),
        send(Chain, for_all,
                 message(W, maximum, ?(Font, width, @arg1))),
        get(W, value, Width),
        send(W, done).

1.109.3 Get methods

number <-catch_all: selector=name, argument=unchecked ... -> copy=number

Makes all send operations available as get operations so that the receiving number is not modified:

?- new(N, number(2)),
   get(N, plus, 3, N2),
   get(N2, value, V2).

V2 = 5
N2 = @1687003/number
N = @1686999/number

First creates a new number object with the same number<-value, invokes the method as a send method and, if the send succeeds, returns the copy.

number <-compare: int|number|real -> {smaller,equal,larger}

Compare to the argument. The result smaller implies the receiver is smaller than the argument. Intended to support chain->sort and friends. To sort a chain of integers by value:

send(Chain, sort, ?(@arg1, compare, @arg2)).