11 Variables

A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text of a Lisp program, variables are written using the syntax for symbols.

In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of its use as a function name. See Symbol Components.

The textual form of a Lisp program is given by the read syntax of the Lisp objects that constitute the program. Hence, a variable in a textual Lisp program is written using the read syntax for the symbol representing the variable.

• Global Variables: Variable values that exist permanently, everywhere.
• Constant Variables: Certain "variables" have values that never change.
• Local Variables: Variable values that exist only temporarily.
• Void Variables: Symbols that lack values.
• Defining Variables: A definition says a symbol is used as a variable.
• Tips for Defining: Things you should think about when you define a variable.
• Accessing Variables: Examining values of variables whose names are known only at run time.
• Setting Variables: Storing new values in variables.
• Variable Scoping: How Lisp chooses among local and global values.
• Buffer-Local Variables: Variable values in effect only in one buffer.
• File Local Variables: Handling local variable lists in files.
• Directory Local Variables: Local variables common to all files in a directory.
• Frame-Local Variables: Frame-local bindings for variables.
• Variable Aliases: Variables that are aliases for other variables.
• Variables with Restricted Values: Non-constant variables whose value can not be an arbitrary Lisp object.