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,
#!optional
and
#!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.