Editing Stack-oriented programming (section)

=== Variables and dictionaries ===
The evaluation of different expressions has already been analysed. The implementation of variables is important for any programming language, but for stack-oriented languages, it is of special concern, as there is only one way to interact with data.

The way variables are implemented in stack-oriented languages such as PostScript usually involves a separate, specialized stack which holds ''dictionaries'' of [[key–value pair|key-value pair]]s. To create a variable, a key (the variable name) must be created first, with which a value is then associated. In PostScript, a name data object is prefixed with a <code>/</code>, so <code>/x</code> is a name data object which can be associated with, for example, the number <code>42</code>. The <code>define</code> command is <code>def</code>, so

<code>/x 42 def</code>

associates with the name <code>x</code> with the number <code>42</code> in the dictionary atop the stack. A difference exists between <code>/x</code> and <code>x</code> – the former is a data object representing a name, and <code>x</code> stands for what is defined under <code>/x</code>.