The following list describes additional notations used in Scheme. See Numbers, for a description of the notations used for numbers.
+ - .
The plus sign, minus sign, and period are used in numbers, and may also occur in an identifier. A delimited period (not occurring within a number or identifier) is used in the notation for pairs and to indicate a “rest” parameter in a formal parameter list (see Lambda Expressions).
Parentheses are used for grouping and to notate lists (see Lists).
The double quote delimits strings (see Strings).
The backslash is used in the syntax for character constants (see Characters) and as an escape character within string constants (see Strings).
The semicolon starts a comment.
The single quote indicates literal data; it suppresses evaluation (see Quoting).
The backquote indicates almost-constant data (see Quoting).
The comma is used in conjunction with the backquote (see Quoting).
A comma followed by an at-sign is used in conjunction with the backquote (see Quoting).
The sharp (or pound) sign has different uses, depending on the character that immediately follows it:
These character sequences denote the boolean constants (see Booleans).
This character sequence introduces a character constant (see Characters).
This character sequence introduces a vector constant (see Vectors). A close parenthesis, ‘)’, terminates a vector constant.
#e #i #b #o #d #l #s #x
These character sequences are used in the notation for numbers (see Numbers).
This character sequence introduces an extended comment. The comment is terminated by the sequence ‘|#’. This notation is an MIT/GNU Scheme extension.
This character sequence is used to denote a small set of named
constants. Currently there are only two of these,
#!rest, both of which are used in the
lambda special form
to mark certain parameters as being “optional” or “rest” parameters.
This notation is an MIT/GNU Scheme extension.
This character sequence introduces a bit string (see Bit Strings). This notation is an MIT/GNU Scheme extension.
This character sequence is used to denote objects that do not have a readable external representation (see Custom Output). A close bracket, ‘]’, terminates the object’s notation. This notation is an MIT/GNU Scheme extension.
This character sequence is a convenient shorthand used to refer to objects by their hash number (see Custom Output). This notation is an MIT/GNU Scheme extension.
These character sequences introduce a notation used to show circular structures in printed output, or to denote them in input. The notation works much like that in Common Lisp, and is an MIT/GNU Scheme extension.