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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