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interfaces

This extension provides a simple abstraction for defining abstract interfaces with separate implementations.

Documentation

interface

 
 [syntax] (interface NAME DEFINITION ...)

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

 
 [syntax] (implementation NAME DEFINITION ...)

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

 
(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))))

Requirements

/eggref/4/records

Author

felix winkelmann

License

 
Copyright (c) 2009, The CHICKEN Team
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

  Redistributions of source code must retain the above copyright notice,
    this list of conditions and the following disclaimer. 
  Redistributions in binary form must reproduce the above copyright notice,
    this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.
  Neither the name of the author nor the names of its contributors may be
    used to endorse or promote products derived from this software without
    specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

Version History
0.2
added missing dependency
0.1
Initial release