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12 Variables

A variable is a name used in a program to stand for a value. In Lisp, each variable is represented by a Lisp symbol (see Symbols). The variable name is simply the symbol’s name, and the variable’s value is stored in the symbol’s value cell1. See Symbol Components. In Emacs Lisp, the use of a symbol as a variable is independent of its use as a function name.

As previously noted in this manual, a Lisp program is represented primarily by Lisp objects, and only secondarily as text. The textual form of a Lisp program is given by the read syntax of the Lisp objects that constitute the program. Hence, the textual form of a variable in a Lisp program is written using the read syntax for the symbol representing the variable.

• Global Variables  Variable values that exist permanently, everywhere.
• Constant Variables  Variables 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.
• Watching Variables  Running a function when a variable is changed.
• 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.
• Connection Local Variables  Local variables common for remote connections.
• 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.
• Generalized Variables  Extending the concept of variables.
  1. To be precise, under the default dynamic scoping rule, the value cell always holds the variable’s current value, but this is not the case under the lexical scoping rule. See Variable Scoping, for details.↩