GNU Emacs Lisp Reference Manual

2.3.4: Symbol Type

A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the name is unique---no two symbols have the same name.

A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently.

A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters `-+=*/'. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a `\' at the beginning of the name to force interpretation as a symbol.) The characters `_~!@$%^&:<>{}' are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, `\t' represents a tab character; in the name of a symbol, however, `\t' merely quotes the letter t. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it's rare to do such a thing.

Common Lisp note: In Common Lisp, lower case letters are always ``folded'' to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct.

Here are several examples of symbol names. Note that the `+' in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the sixth example because the rest of the name makes it invalid as a number.

foo                 ; A symbol named `foo'.
FOO                 ; A symbol named `FOO', different from `foo'.
char-to-string      ; A symbol named `char-to-string'.
1+                  ; A symbol named `1+'
                    ;   (not `+1', which is an integer).
\+1                 ; A symbol named `+1'
                    ;   (not a very readable name).
\(*\ 1\ 2\)         ; A symbol named `(* 1 2)' (a worse name).
+-*/_~!@$%^&=:<>{}  ; A symbol named `+-*/_~!@$%^&=:<>{}'.
                    ;   These characters need not be escaped.