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Article contents:[[tags: manual]] [[toc:]] == Extensions to the R7RS standard === Brackets and braces The brackets {{[ ... ]}} and the braces {{ { ... } }} are provided as an alternative syntax for {{( ... )}}. A number of reader extensions is provided. === User defined character names User defined character names are supported. See {{char-name}}. Numeric hexadecimal character codes above are supported and can be read using ''#\uXXXX'' and ''#\UXXXXXXXX'', in addition to the standard ''\x...;'' notation. Non-standard characters names supported are {{#\linefeed}}, {{#\vtab}}, {{#\nul}}, {{#\page}} and {{#\esc}}. == Non-standard read syntax === Multiline Block Comment <read>#|</read> #| ... |# A multiline ''block'' comment. May be nested. Implements [[http://srfi.schemers.org/srfi-30/srfi-30.html|SRFI-30]]. === Expression Comment <read>#;</read> #;EXPRESSION Treats {{EXPRESSION}} as a comment. That is, the comment runs through the whole S-expression, regardless of newlines, which saves you from having to comment out every line, or add a newline in the middle of your parens to make the commenting of the last line work, or other things like that. Implements [[http://srfi.schemers.org/srfi-62/srfi-62.html|SRFI-62]]. === External Representation <read>#,</read> #,(CONSTRUCTORNAME DATUM ...) Allows user-defined extension of external representations. (For more information see the documentation for [[http://srfi.schemers.org/srfi-10/srfi-10.html|SRFI-10]]) === Location Expression <read> #$EXPRESSION</read> An abbreviation for {{(location EXPRESSION)}}. === Bytevector strings <read>#u8"..."</read> String syntax for bytevectors, as an alternative to {{#u8(...)}}. The usual escape sequences for strings are recognized. === Keyword <read>#:</read> #:SYMBOL SYMBOL: :SYMBOL Syntax for keywords. Keywords are symbols that evaluate to themselves, and as such don't have to be quoted. Either {{SYMBOL:}} or {{:SYMBOL}} is accepted, depending on the setting of the {{keyword-style}} parameter, but never both. {{#:SYMBOL}} is always accepted. === Multiline String Constant <read>#<<</read> #<<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 <read>#<#</read> #<#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 <read>#></read> #> ... <# Abbreviation for {{(foreign-declare " ... ")}}. === String escape sequences String-literals may contain the following escape sequences: <table style="margin-top: 1em; max-width: 40em"> <tr><th>Escape sequence</th><th>Character</th></tr> <tr><td>{{\n}}</td><td>line feed / newline</td></tr> <tr><td>{{\t}}</td><td>tab</td></tr> <tr><td>{{\r}}</td><td>carriage return</td></tr> <tr><td>{{\b}}</td><td>backspace</td></tr> <tr><td>{{\a}}</td><td>bell</td></tr> <tr><td>{{\v}}</td><td>vertical tab</td></tr> <tr><td>{{\f}}</td><td>form feed</td></tr> <tr><td>{{\x}}''XX;''</td><td>hexadecimal 8-bit character code</td></tr> <tr><td>{{\u}}''XXXX''</td><td>hexadecimal 16-bit Unicode character code</td></tr> <tr><td>{{\U}}''XXXXXXXX''</td><td>hexadecimal 32-bit Unicode character code</td></tr> <tr><td>{{\}}''OOO''</td><td>octal 8-bit character code</td></tr> <tr><td>{{\|}}   {{\"}}    {{\\}}    {{\'}}</td><td>the escaped character</td></tr> </table> === Bang <read>#!</read> #!... 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 === Conditional Expansion <read>#+</read> #+FEATURE EXPR Rewrites to (cond-expand (FEATURE EXPR) (else)) and performs the feature test at macroexpansion time. Therefore, it may not work as expected when used within a macro form. --- Previous: [[Deviations from the standard]] Next: [[Interface to external functions and variables]] Description of your changes:

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