You are looking at historical revision 3679 of this page. It may differ significantly from its current revision.

• egg

Introduction

POS is a portable object system for Scheme.

Requirements

An implementation of syntax-rules (syntax-case, syntactic-closures or alexpander)

Documentation

 POS offers the following features:

 1.  It is very portable

  Only uses R5RS standard facilities including define-syntax/syntax-rules

 2.  Very small

  Consists of only 1 constant, 1 function and 1 macro

 3.  Supports the following OO features

  a.  multiple inheritance
  b.  class and instance variables and methods
  c.  strong instance and class variable encapsulation
  d.  very easy instance variable access from within methods
  e.  very simple to use
  f.  no MOP

 4.  Open source and freely available

 Classes are defined with a single macro as follows:

 (define-class	class-name   [class-defn-clause] ...)

 class-name:  the name of the new class (as a symbol)

  example:   myclass

 class-defn-clause consists of any combination of class definition
 clauses in any order.  The following lists the various types
 available.

 class-variables: a list of class variables with initial values (in let
 format).  The 'cvars' is a required literal.

  example:  (cvars
	      (a 1)
	      (b 2))

 instance-variables: a list of instance variables with initial values (in let
 format).  The 'ivars' is a required literal.

  example:  (ivars
	      (c 3)
	      (d 4))

 class-methods:  a list of class method definitions in the format:
 The 'cmeths' is a required literal.

  (cmeths
     meth1  meth2  ...  )

 where each meth looks as follows:

  (meth-name (self arg1 arg2 ...)
	  code...)

 instance-methods:  have the same format as class-methods except that
 the literal 'imeths' is used.

 Built-in class methods:

  'name  ;;  returns the string name of the class

  'super 'meth arg1 ...  ;; executes a super-method (meth)

  'class  ;; return #f (so you know you have a class object)

 Built-in instance methods:

  'class  ;; returns the class object of the instance

  'super 'meth arg1 ...  ;; executes a super-method (meth)

 Instance variables defined in the class where the instance method is
 defined are accessible (set or get) as any other local variable.

 Class variables defined in the class where the class method is defined
 are accessible (set or get) as any other local variable.  Class methods
 and class variables work analogously to their instance counter parts
 as they should (contrary to Java).

 'self' can be used as in other OO languages.  'self' in class methods
 refers to the class object.

 Execution of methods on an object (class or instance):

  (object  'method  arg1  arg2  ...)

 Creation of new instances can occur in two ways.  The first way is to
 use use the primitive function "make" as follows:

  (define ins (make <myclass>))

 This creates an instance of the <myclass> class with all instance
 variables set to their default values and no special processing.

 The other way is to create a class method which takes potential
 arguments, creates a new instance, and performs any additional
 initialization processes.  See example-02.scm for an example of this.

 Note that the <> around class names is just a convention and not
 necessary.

License

Copyright (c) 2006 Blake McBride (blake@mcbride.name)
All rights reserved.
 
Free for any use so long as this note remains intact.

No warranty of any kind either express or implied.
Use at your own risk.

Author

Blake McBride (blake(at)mcbride(dot)name)

History

1.0

Initial release