2.1 Identifiers

Most identifiers allowed by other programming languages are also acceptable to Scheme. The precise rules for forming identifiers vary among implementations of Scheme, but in all implementations a sequence of letters, digits, and “extended alphabetic characters” that begins with a character that cannot begin a number is an identifier. In addition, +, -, and ... are identifiers. Here are some examples of identifiers:

     
     lambda                   q
     list->vector             soup
     +                        V17a
     <=?                      a34kTMNs
     the-word-recursion-has-many-meanings
     

Extended alphabetic characters may be used within identifiers as if they were letters. The following are extended alphabetic characters:

     
     ! $ % & * + - . / : < = > ? @ ^ _ ~

See section Lexical structure for a formal syntax of identifiers.

Identifiers have two uses within Scheme programs:

• Any identifier may be used as a variable or as a syntactic keyword (see sections see Variables; syntactic keywords; and regions and see Macros).
• When an identifier appears as a literal or within a literal (see section see Literal expressions), it is being used to denote a symbol (see section see Symbols).