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.
Go to the first, previous, next, last section, table of contents.