XPCE Reference Manual: Section 1.11

1.11 class binary_expression

Binary arithmetic expression with binary_expression<-left and binary_expression<-right operants. Class binary_expression has the subclasses

+ Addition

- Subtraction and negation

Multiplication

/ Division

PCE expression objects are first of all designed for supporting graphics calculations. The intermediate results are calculated in fixed-point arithmetic (1/1024 resolution). The result is rounded to the nearest integer value.

Binary expressions are used by class = for the definition of equations used by class spatial. The are also used by class handle and class region to express locations in terms of the dimensions of a related graphical object. Finally, they may be used as function objects in methods.

Note that type conversion converts function objects (and thus also binary expressions) into the value they evaluate too. This implies that

send(Box, size, size(W+2, H+2))

Is a comfortable way to do (graphics) calculations in PCE/Prolog. It must be noted that

W1 is W + 2,
H1 is H + 2,
send(Box. size, size(W1, H1))

is, in generally faster as the first example creates two PCE expressions evaluates then and then destroys them again.

Bugs:

Evaluation of expressions is written in C, bypassing the message passing of PCE. This implies the user cannot define new expression classes.

See also: - class real
- class number

1.11.1 Instance variables

binary_expression <-> left: expression: Operants of the expression. See class binary_condition for a description of the type expression.
binary_expression <-> right: expression: Inherits description from: binary_expression-left

1.11.2 Send methods

binary_expression ->initialise: left=expression, right=expression: Create the expression from its binary_expression<-left and binary_expression<-right operator. As class binary_expression itself does not define evaluation there is little use in creating instances of this class.

1.11.3 Get methods

binary_expression <-value: binding== ... -> value=int|number|real

Determine the value of the expression given the values for the var objects appearing in it. Used by class handle and class region. Example:

?- get(x + 5, value, x=3, X).       ==> X = 8

Note: in this example we can simply write x instead of new(X, var(x)) as x is the name of a predefined var object. See class var.