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Non-standard read syntax

Multiline Block Comment

#| ... |# 

A multiline block comment. May be nested. Implements SRFI-30

Expression Comment

#;EXPRESSION

Treats EXPRESSION as a comment.

External Representation

#,(CONSTRUCTORNAME DATUM ...)

Allows user-defined extension of external representations. (For more information see the documentation for SRFI-10)

Syntax Expression

#'EXPRESSION

An abbreviation for (syntax EXPRESSION).

Location Expression

#$EXPRESSION

An abbreviation for (location EXPRESSION).

Keyword

#:SYMBOL

Syntax for keywords. Keywords are symbols that evaluate to themselves, and as such don't have to be quoted.

Multiline String Constant

#<<TAG

Specifies a multiline string constant. Anything up to a line equal to TAG (or end of file) will be returned as a single string:

(define msg #<<END
 "Hello, world!", she said.
END
)

is equivalent to

(define msg "\"Hello, world!\", she said.")

Multiline String Constant with Embedded Expressions

#<#TAG

Similar to #<<, but allows substitution of embedded Scheme expressions prefixed with # and optionally enclosed in curly brackets. Two consecutive #s are translated to a single #:

(define three 3)
(display #<#EOF
This is a simple string with an embedded `##' character
and substituted expressions: (+ three 99) ==> #(+ three 99)
(three is "#{three}")
EOF
)

prints

This is a simple string with an embedded `#' character
and substituted expressions: (+ three 99) ==> 102
(three is "3")

Foreign Declare

#> ... <#

Abbreviation for foreign-declare " ... ").

Sharp Prefixed Symbol

#%... 

Reads like a normal symbol.

Bang

#!... 

Interpretation depends on the directly following characters. Only the following are recognized. Any other case results in a read error.

Line Comment

• If followed by whitespace or a slash, then everything up the end of the current line is ignored

Eof Object

• If followed by the character sequence eof, then the (self-evaluating) end-of-file object is returned

DSSSL Formal Parameter List Annotation

• If followed by any of the character sequences optional, rest or key, then a symbol with the same name (and prefixed with #!) is returned

Read Mark Invocation

• If a read mark with the same name as the token is registered, then its procedure is called and the result of the read-mark procedure will be returned

Case Sensitive Expression

#cs...

Read the next expression in case-sensitive mode (regardless of the current global setting).

Case Insensitive Expression

#ci...

Read the next expression in case-insensitive mode (regardless of the current global setting).

Conditional Expansion

#+FEATURE EXPR

Equivalent to

(cond-expand (FEATURE EXPR) (else))

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