1.3.7 Additional Notations
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:
     
 
- #t #f
- 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, #!optionaland#!rest, both of which are used in thelambdaspecial 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.