Several defining constructs appear in CLIPS: defmodule, defrule, deffacts, deftemplate, defglobal, deffunction, defclass, definstances, defmessagehandler, defgeneric, and defmethod. All constructs in CLIPS are surrounded by parentheses. The construct opens with a left parenthesis and closes with a right parenthesis. Defining a construct differs from calling a function primarily in effect. Typically a function call leaves the CLIPS environment unchanged (with some notable exceptions such as resetting or clearing the environment or opening a file). Defining a construct, however, is explicitly intended to alter the CLIPS environment by adding to the CLIPS knowledge base. Unlike function calls, constructs never have a return value.
As with any programming language, it is highly beneficial to comment
CLIPS code. All constructs (with the exception of defglobal) allow
a comment directly following the construct name. Comments also
can be placed within CLIPS code by using a semicolon (;).
Everything from the semicolon until the next return
character will be ignored by CLIPS. If the semicolon is the first
character in the line, the entire line will be treated as a comment.
Examples of commented code will be provided throughout the reference
manual. Semicolon commented text is not saved by CLIPS when loading
constructs (however, the optional comment string within a construct
is saved).