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</dd>
<dt>
-<a href="#sec25">Procedural Only Where Neccesary</a>
+<a href="#sec25">Procedural Only Where Necessary</a>
</dt>
<dt>
<a href="#sec26">Real World</a>
</dl>
</dd>
<dt>
-<a href="#sec30">Sources &amp; Further Reading</a>
+<a href="#sec30">Sources and Further Reading</a>
</dt>
<dd>
<dl>
</dt>
</dl>
</dd>
+<dt>
+<a href="#sec39">Software</a>
+</dt>
+<dd>
+<dl>
+<dt>
+<a href="#sec40">Closer to MOP</a>
+</dt>
+</dl>
+</dd>
</dl>
</dd>
</dl>
</div>
-<!-- Page published by Emacs Muse begins here --><p>In Fall of 2006 I did a small project on Metaobject Protocols for my
+<!-- Page published by Emacs Muse begins here -->
+<p>In Fall of 2006 I did a small project on Metaobject Protocols for my
CS 331 class. Here lie my notes which may perhaps be useful to
others. I hope to expand them into something more useful over time.</p>
((bar <span class="emacs-face-builtin">:accessor</span> bar-of <span class="emacs-face-builtin">:initform</span> (list 1 2 3))))
</pre>
-<p>Slot defintions have several options; the above example shows only the
+<p>Slot definitions have several options; the above example shows only the
<code>:accessor</code> and <code>:initform</code> options which are the most commonly
used. <code>:accessor</code> generates an accessor for the slot (e.g. if you have
an instance of <code>example</code> you can <code>(setf (foo-of some-example-instance)
(options) ...)
(<span class="emacs-face-keyword">defmethod</span> <span class="emacs-face-function-name">generic-name</span> ((parameter type) parameter ...)
- <span class="emacs-face-string">"documentation string"</span>
+ <span class="emacs-face-doc">"documentation string"</span>
body)
(<span class="emacs-face-keyword">defgeneric</span> <span class="emacs-face-function-name">foo</span> (bar baz quux)
- (<span class="emacs-face-builtin">:documentation</span> <span class="emacs-face-string">"Process the baz with the quux capacitor to make the
+ (<span class="emacs-face-builtin">:documentation</span> <span class="emacs-face-doc">"Process the baz with the quux capacitor to make the
foo widget fly into the sky at warp speed"</span>))
(<span class="emacs-face-keyword">defmethod</span> <span class="emacs-face-function-name">foo</span> ((bar example) baz (quux capacitor))
programs. Many of them are merely methods to get around deficiencies
in the language, and can be quite messy to implement in some
languages. Ideally a pattern would be subsumed by the language, but
-real world contraints require language standards to remain fairly
+real world constraints require language standards to remain fairly
static.</p>
<pre class="src">
(<span class="emacs-face-keyword">defgeneric</span> <span class="emacs-face-function-name">example-inspect</span> (instance)
- (<span class="emacs-face-builtin">:documentation</span> <span class="emacs-face-string">"Simple object inspector using CLOS MOP"</span>))
+ (<span class="emacs-face-builtin">:documentation</span> <span class="emacs-face-doc">"Simple object inspector using CLOS MOP"</span>))
(<span class="emacs-face-keyword">defmethod</span> <span class="emacs-face-function-name">example-inspect</span> ((instance t))
(format t <span class="emacs-face-string">"Simple Object~% Value: ~S~%"</span> instance))
implementing methods which override certain aspects of the language
behavior. This class of MOPs are what make MOPs especially
powerful. No longer must a problem be restructured to fit the
-implementation language; the underyling language can be reshaped to
+implementation language; the underlying language can be reshaped to
fit the task at hand, and obfuscation of the intended structure of the
application can be avoided.</p>
<p>In a language lacking a MOP, implementing the observer pattern
requires modifying every accessor of a class to explicitly invoke any
-observers, and neccesitates the addition of a mixin class to the class
-heirarchy. The fact that an object can be observed is a meta property
+observers, and necessitates the addition of a mixin class to the class
+hierarchy. The fact that an object can be observed is a meta property
of the class, and forcing it to be implemented at the application
-level dirties the inheritance heirarchy and adds uneccesary meta
+level dirties the inheritance hierarchy and adds unnecessary meta
details to the program.</p>
<pre class="src">
<span class="emacs-face-comment-delimiter">;;; </span><span class="emacs-face-comment">This metaclass adds a slot to instances which use it, and so the
</span><span class="emacs-face-comment-delimiter">;;; </span><span class="emacs-face-comment">system is defined in its own package to avoid name conflicts
</span>(<span class="emacs-face-keyword">defpackage</span> <span class="emacs-face-type">:observer</span>
- (<span class="emacs-face-builtin">:use</span> <span class="emacs-face-builtin">:cl</span> #+sbcl <span class="emacs-face-builtin">:sb-mop</span>)
+ (<span class="emacs-face-builtin">:use</span> <span class="emacs-face-builtin">:cl</span> <span class="emacs-face-builtin">:c2mop</span>)
(<span class="emacs-face-builtin">:export</span> observable register-observer unregister-observer))
(<span class="emacs-face-keyword">in-package</span> <span class="emacs-face-builtin">:observer</span>)
<span class="emacs-face-comment-delimiter">;;; </span><span class="emacs-face-comment">Metaclass
</span>(<span class="emacs-face-keyword">defclass</span> <span class="emacs-face-type">observable</span> (standard-class)
()
- (<span class="emacs-face-builtin">:documentation</span> <span class="emacs-face-string">"Metaclass for observable objects"</span>))
+ (<span class="emacs-face-builtin">:documentation</span> <span class="emacs-face-doc">"Metaclass for observable objects"</span>))
(<span class="emacs-face-keyword">defmethod</span> <span class="emacs-face-function-name">compute-slots</span> ((class observable))
- <span class="emacs-face-string">"Add a slot for storing observers to observable instances"</span>
+ <span class="emacs-face-doc">"Add a slot for storing observers to observable instances"</span>
(cons (make-instance 'standard-effective-slot-definition
<span class="emacs-face-builtin">:name</span> 'observers
<span class="emacs-face-builtin">:initform</span> '(make-hash-table)
slot-name)
(gethash slot-name (slot-value instance 'observers)))
-(<span class="emacs-face-keyword">defmethod</span> (<span class="emacs-face-function-name">setf slot-value-using-class)</span> <span class="emacs-face-builtin">:before</span> (new-value
+(<span class="emacs-face-keyword">defmethod</span> (<span class="emacs-face-function-name">setf slot-value-using-class</span>) <span class="emacs-face-builtin">:before</span> (new-value
(class observable)
instance
slot)
<h3><a name="sec25" id="sec25"></a>
-Procedural Only Where Neccesary</h3>
+Procedural Only Where Necessary</h3>
-<p class="first">Some operations like method invocation are inheretly stateful and so
+<p class="first">Some operations like method invocation are inherently stateful and so
must use a procedural protocol. There is no benefit to be gained from
using a functional protocol, and indeed an attempt would result in
-obtuse code that severely restricted the implementian. Do note that
+obtuse code that severely restricted the implementation. Do note that
only a very small part of method invocation is stateful (the actual
call), and most of it can be implemented functionally (e.g. computing
the discriminating function).</p>
<h4><a name="sec27" id="sec27"></a>
<a href="http://common-lisp.net/project/ucw/">UCW</a> and <a href="http://common-lisp.net/project/bese/arnesi.html">Arnesi</a></h4>
-<p class="first">Arnesi uses the CLOS MOP to implement methods which are transparantly
+<p class="first">Arnesi uses the CLOS MOP to implement methods which are transparently
rewritten into continuation passing style. This allows their execution
to be suspended at certain points and resumed later. UCW builds on top
of this to support a web framework where the statelessness of http is
<h4><a name="sec29" id="sec29"></a>
<a href="http://common-lisp.net/project/elephant/">Elephant</a></h4>
-<p class="first">Elephant uses the CLOS MOP to transparantly store any class to disk
+<p class="first">Elephant uses the CLOS MOP to transparently store any class to disk
and handle paging between the disk store and memory efficiently
without user intervention.</p>
<h2><a name="sec30" id="sec30"></a>
-Sources &amp; Further Reading</h2>
+Sources and Further Reading</h2>
<h3><a name="sec31" id="sec31"></a>
Sources</h3>
+<h3><a name="sec39" id="sec39"></a>
+Software</h3>
+
+<h4><a name="sec40" id="sec40"></a>
+<a href="http://common-lisp.net/project/closer/closer-mop.html">Closer to MOP</a></h4>
+
+<p class="first">Compatibility layer that attempts to present the <em>Art of the Metaobject
+Protocol</em> MOP specification properly in as many Common Lisp
+implementation as possible.</p>
+
+
+
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