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Article contents:[[tags: manual]] [[toc:]] == Extensions to the R5RS standard === Identifiers Identifiers may contain special characters if delimited with {{| ... |}}. === Brackets and braces The brackets {{[ ... ]}} and the braces {{ { ... } }} are provided as an alternative syntax for {{( ... )}}. A number of reader extensions is provided. === Non-standard procedures and syntax CHICKEN provides numerous non-standard procedures. See the manual sections on the included library modules ([[Included modules]]) for more information. Here we only document {{cond-expand}} because it is always present in a module, even without imports. ==== cond-expand <macro>(cond-expand FEATURE-CLAUSE ...)</macro> Expands by selecting feature clauses. This form is allowed to appear in non-toplevel expressions. Predefined feature-identifiers are "situation" specific: ; compile : {{chicken}}, {{chicken-5}}, {{compiling}}, {{library}}, {{eval}}, {{extras}}, {{regex}}, {{srfi-0}}, {{srfi-2}}, {{srfi-4}}, {{srfi-6}}, {{srfi-8}}, {{srfi-9}}, {{srfi-10}}, {{srfi-11}}, {{srfi-12}}, {{srfi-15}}, {{srfi-16}}, {{srfi-17}}, {{srfi-23}}, {{srfi-26}}, {{srfi-28}}, {{srfi-30}}, {{srfi-31}}, {{srfi-39}}, {{srfi-55}}, {{srfi-61}}, {{srfi-62}} ; load : {{chicken}}, {{chicken-5}}, {{extras}}, {{srfi-0}}, {{srfi-2}}, {{srfi-6}}, {{srfi-8}}, {{srfi-9}}, {{srfi-10}}, {{srfi-12}}, {{srfi-17}}, {{srfi-23}}, {{srfi-28}}, {{srfi-30}}, {{srfi-39}}, {{srfi-55}}, {{srfi-61}}, {{srfi-62}}. {{library}} is implicit. ; eval : {{csi}}, {{chicken}}, {{chicken-5}}, {{extras}}, {{srfi-0}}, {{srfi-2}}, {{srfi-6}}, {{srfi-8}}, {{srfi-9}}, {{srfi-10}}, {{srfi-11}}, {{srfi-12}}, {{srfi-15}}, {{srfi-16}}, {{srfi-17}}, {{srfi-23}}, {{srfi-26}}, {{srfi-28}}, {{srfi-30}}, {{srfi-31}}, {{srfi-39}}, {{srfi-55}}, {{srfi-61}}, {{srfi-62}}. {{library}} is implicit. Also, features of the form {{chicken-5.X}}, where {{X}} denotes the minor version, are available. The symbols returned by the following procedures from [[Module (chicken platform)|(chicken platform)]] are also available as feature-identifiers in all situations: {{(machine-byte-order)}}, {{(machine-type)}}, {{(software-type)}}, {{(software-version)}}. For example, the {{machine-type}} class of feature-identifiers include {{arm}}, {{alpha}}, {{mips}}, etc. The [[Module (chicken platform)|(chicken platform)]] module also provides a function {{(features)}} that returns a list of all registered features. In addition the following feature-identifiers may exist: {{cross-chicken}}, {{dload}}, {{manyargs}}, {{ptables}}. For further information, see the documentation for [[http://srfi.schemers.org/srfi-0/srfi-0.html|SRFI-0]]. === User defined character names User defined character names are supported. See {{char-name}}. Characters can be given in hexadecimal notation using the ''#\xXX'' syntax where ''XX'' specifies the character code. Character codes above 255 are supported and can be read (and are written) using the ''#\uXXXX'' and ''#\UXXXXXXXX'' notations. Non-standard characters names supported are {{#\tab}}, {{#\linefeed}}, {{#\return}}, {{#\alarm}}, {{#\vtab}}, {{#\nul}}, {{#\page}}, {{#\esc}}, {{#\delete}} and {{#\backspace}}. === Special characters in strings CHICKEN supports special characters preceded with a backslash ''\'' in quoted string constants. ''\n'' denotes the newline-character, ''\r'' carriage return, ''\b'' backspace, ''\t'' TAB, ''\v'' vertical TAB, ''\a'' alarm, ''\f'' formfeed, ''\xXX'' a character with the code {{XX}} in hex and ''\uXXXX'' (and ''\UXXXXXXXX'') a unicode character with the code {{XXXX}}. The latter is encoded in UTF-8 format. == Non-standard read syntax === Escapes in symbols {{| ... |}} may be used to escape a sequence of characters when reading a symbol. {{\X}} escapes a single character in a symbols name: (symbol->string '|abc def|) => "abc def" (symbol->string '|abc||def|) => "abcdef" (symbol->string '|abc|xyz|def|) => "abcxyzdef" (symbol->string '|abc\|def|) => "abc|def" (symbol->string 'abc\ def) => "abc def" === 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> #$EXPRESSION</read> An abbreviation for {{(location EXPRESSION)}}. === Blob literals <read>#${</read> #${ HEX ... } Syntax for literal "blobs" (byte-sequences). Expects hexadecimal digits and ignores any whitespace characters: #;1> ,d '#${deadbee f} blob of size 4: 0: de ad be ef .... === Keyword <read>#:</read> #:SYMBOL SYMBOL: :SYMBOL Syntax for keywords. Keywords are symbol-like objects 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 === Case Sensitive Expression <read>#cs</read> #cs... Read the next expression in case-sensitive mode (regardless of the current global setting). === Case Insensitive Expression <read>#ci</read> #ci... Read the next expression in case-insensitive mode (regardless of the current global setting). === 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: [[Debugging]] Description of your changes:

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