Sharpsign is a non-terminating dispatching macro character. It reads an optional sequence of digits and then one more character, and uses that character to select a function to run as a reader macro function.
The standard syntax includes constructs introduced by the # character. The syntax of these constructs is as follows: a character that identifies the type of construct is followed by arguments in some form. If the character is a letter, its case is not important; #O and #o are considered to be equivalent, for example.
Certain # constructs allow an unsigned decimal number to appear between the # and the character.
The reader macros associated with the dispatching macro character # are described later in this section and summarized in the next figure.
dispatch char purpose dispatch char purpose
Backspace signals error { undefined*
Tab signals error } undefined*
Newline signals error + read-time conditional
Linefeed signals error - read-time conditional
Page signals error . read-time evaluation
Return signals error / undefined
Space signals error A, a array
! undefined* B, b binary rational
" undefined C, c complex number
# reference to = label D, d undefined
$ undefined E, e undefined
% undefined F, f undefined
& undefined G, g undefined
' function abbreviation H, h undefined
( simple vector I, i undefined
) signals error J, j undefined
* bit vector K, k undefined
, undefined L, l undefined
: uninterned symbol M, m undefined
; undefined N, n undefined
< signals error O, o octal rational
= labels following object P, p pathname
> undefined Q, q undefined
? undefined* R, r radix-n rational
@ undefined S, s structure
[ undefined* T, t undefined
\ character object U, u undefined
] undefined* V, v undefined
^ undefined W, w undefined
_ undefined X, x hexadecimal rational
` undefined Y, y undefined
| balanced comment Z, z undefined
~ undefined Rubout undefined
Figure 2-19. Standard #Dispatching Macro Character Syntax
The combinations marked by an asterisk (*) are explicitly reserved to the user. No conforming implementation defines them.
Note also that digits do not appear in the preceding table. This is because the notations #0, #1, ..., #9 are reserved for another purpose which occupies the same syntactic space. When a digit follows a sharpsign, it is not treated as a dispatch character. Instead, an unsigned integer argument is accumulated and passed as an argument to the reader macro for the character that follows the digits. For example, #2A((1 2) (3 4)) is a use of #A with an argument of 2.