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Article contents:[[toc:]] [[tags: eggs]] == interfaces This extension provides a simple abstraction for defining abstract interfaces with separate implementations. === Documentation ==== interface <macro>(interface NAME DEFINITION ...)</macro> Declares {{NAME}} to be an ''interface'' that provides the definitions {{DEFINITION ...}}. {{DEFINITION}} should be a value definition of the form (define NAME [VALUE]) or (define (NAME VAR ...) [BODY ...]) The values and bodies of the given definitions are optional and default to {{(void)}} (for value definitions) or a procedure that signals a runtime error (for procedure definitions). If a value/body is given, it provides a default for later implementations of this interface (see below). ==== implementation <macro>(implementation NAME DEFINITION ...)</macro> Defines an ''implementation'' of interface {{NAME}}. An implementation is a record structure holding the given definitions. Note that {{implementation}} returns a first-class object, in contrast to {{interface}} which is a declaration. Each definition declared in the interface can be accessed by invoking the definition-name with an implementation as its sole argument. === Example <enscript highlight=scheme> (interface counter (define (counter-new)) (define (counter-inc c)) (define (counter-get c))) (define simple-counter (implementation counter (define (counter-new) 0) (define counter-inc add1) (define counter-get identity))) (let ((c1 ((counter-new simple-counter)))) (print ((counter-get simple-counter) c1)) ; ==> "0" (let ((c2 ((counter-inc simple-counter) c1))) (print ((counter-get simple-counter) c2)))) ; ==> "1" (define logged-counter (implementation counter (define (counter-inc c) (let ((c2 (add1 c))) (print "increasing counter " c " to " c2 "! is this cool or what?") c2)))) </enscript> === Requirements [[records]] == Author [[/users/felix winkelmann|felix winkelmann]] == Repository This egg is hosted on the CHICKEN Subversion repository: [[https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/interfaces|https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/interfaces]] If you want to check out the source code repository of this egg and you are not familiar with Subversion, see [[/egg-svn-checkout|this page]]. == License This code is in the public domain == Version History ; 0.4 : ported to CHICKEN 5 ; 0.3 : fixed bug related to implementation constructors exported from modules ; 0.2 : added missing dependency ; 0.1 : Initial release Description of your changes:

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