Editing BETA (programming language) (section)

===Patterns===
A major and peculiar feature of the language is the concept of patterns. In another programming language, such as [[C++]], one would have several classes and procedures. BETA expresses both of these concepts using patterns.

For example, a simple class in C++ would have the form
<syntaxhighlight lang="cpp">
class point {
    int x, y;
};
</syntaxhighlight>
In BETA, the same class could be represented by the pattern
<!-- This isn't Pascal, but syntax is similar -->
<syntaxhighlight lang="pascal">
point: (#
    x, y: @integer
#)
</syntaxhighlight>
That is, a class called ''point'' will have two fields, ''x'' and ''y'', of type [[integer (computer science)|integer]]. The symbols ''(#'' and ''#)'' introduce patterns. The colon is used to declare patterns and variables. The ''@'' sign before the integer type in the field definitions specifies that these are integer fields, and not, by contrast, references, arrays or other patterns.

As another comparison, a procedure in C++ could have the form
<syntaxhighlight lang="cpp">
int max(int x, int y)
{
    if (x >= y)
    {
        return x;
    }
    else
    {
        return y;
    }
}
</syntaxhighlight>
In BETA, such a function could be written using a pattern
<!-- This isn't Pascal, but syntax is similar -->
<syntaxhighlight lang="pascal">
max: (#
    x, y, z: @integer
enter (x, y)
do
    (if x >= y // True then
        x -> z
    else
        y -> z
    if)
exit z
#)
</syntaxhighlight>
The ''x'', ''y'' and ''z'' are local variables. The '''enter''' keyword specifies the input parameters to the pattern, while the '''exit''' keyword specifies the result of the function. Between the two, the '''do''' keyword prefixes the sequence of operations to be made. The conditional block is delimited by ''(if'' and ''if)'', that is the '''if''' keyword becomes part of the opening and closing parenthesis. Truth is checked through ''// True'' within an if block. Finally, the assignment operator ''-&gt;'' assigns the value on its left hand side to the variable on its right hand side.