3.4.3.4 Identifiers

Most identifiers allowed by other programming languages are also acceptable to Scheme. In general, a sequence of letters, digits, and “extended alphabetic characters” is an identifier when it begins with a character that cannot begin a representation of a number object. In addition, +, -, and ... are identifiers, as is a sequence of letters, digits, and extended alphabetic characters that begins with the two–character sequence ->. Here are some examples of identifiers:

lambda         q                soup
list->vector   +                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:

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

Moreover, all characters whose Unicode scalar values are greater than 127 and whose Unicode category is Lu, Ll, Lt, Lm, Lo, Mn, Mc, Me, Nd, Nl, No, Pd, Pc, Po, Sc, Sm, Sk, So, or Co can be used within identifiers. In addition, any character can be used within an identifier when specified via an ?inline-hex-escape. For example, the identifier H\x65;llo is the same as the identifier Hello.

Any identifier may be used as a variable or as a syntactic keyword (scheme basic variables keywords regions and scheme syntax macros) in a Scheme program. Any identifier may also be used as a syntactic datum, in which case it represents a symbol (baselib symbols).