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 Figure 2–19.
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
.