Outdated CHICKEN release

This is a manual page for an old and unsupported version of CHICKEN. If you are still using it, please consider migrating to the latest version. You can find the manual for the latest release here.

manual

Outdated CHICKEN release
Non-standard read syntax

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] #|

#| ... |#

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

Expression Comment

[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 SRFI-62.

External Representation

[read] #,

#,(CONSTRUCTORNAME DATUM ...)

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

Location Expression

#$EXPRESSION

An abbreviation for (location EXPRESSION).

Blob literals

[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] #:

#: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] #<<

#<<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] #<#

#<#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] #>

#> ... <#

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

String escape sequences

String-literals may contain the following escape sequences:

Escape sequence	Character
`\n`	line feed / newline
`\t`	tab
`\r`	carriage return
`\b`	backspace
`\a`	bell
`\v`	vertical tab
`\f`	form feed
`\x`XX	hexadecimal 8-bit character code
`\u`XXXX	hexadecimal 16-bit Unicode character code
`\U`XXXXXXXX	hexadecimal 32-bit Unicode character code
`\`OOO	octal 8-bit character code
`\\|` `\"` `\\` `\'`	the escaped character

Sharp Prefixed Symbol

[read] #%

#%...

Reads like a normal symbol.

Bang

[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

#cs...

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

Case Insensitive Expression

[read] #ci

#ci...

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

Conditional Expansion

[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: Extensions to the standard

Next: Non-standard macros and special forms