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* "No definition" for "per-file basis in a source code block" mode
@ 2013-04-15  8:34 Wolfkin Chiang
  2013-04-15 11:38 ` Suvayu Ali
  0 siblings, 1 reply; 3+ messages in thread
From: Wolfkin Chiang @ 2013-04-15  8:34 UTC (permalink / raw)
  To: emacs-orgmode


[-- Attachment #1.1: Type: text/plain, Size: 1303 bytes --]

Hi, All,

While I try the "per-file basis in a source code block" mode,
It tells me:
No definition for class `per-file-class' in `org-export-latex-classes'
Please help me to resolve it, thanks!

I command
$ emacs -D -nw --no-splash --batch --kill --file list.org --funcall
org-export-as-latex
And it tells me:
Loading 00debian-vars...
Loading /etc/emacs/site-start.d/50asymptote.el (source)...
Loading /etc/emacs/site-start.d/50dictionaries-common.el (source)...
Loading debian-ispell...
Loading /var/cache/dictionaries-common/emacsen-ispell-default.el (source)...
Loading /var/cache/dictionaries-common/emacsen-ispell-dicts.el (source)...
Loading /etc/emacs/site-start.d/50emacs-goodies-el.el (source)...
Loading /etc/emacs/site-start.d/50geiser.el (source)...
Loading /etc/emacs/site-start.d/50latex-cjk-common.el (source)...
Loading cjk-enc...
Loading /etc/emacs/site-start.d/50latex-cjk-thai.el (source)...
Loading /etc/emacs/site-start.d/50org-mode.el (source)...
Loading /etc/emacs/site-start.d/50python-docutils.el (source)...
Loading /etc/emacs/site-start.d/50thailatex.el (source)...
OVERVIEW
Exporting to LaTeX...
No definition for class `per-file-class' in `org-export-latex-classes'

And it is true that this can be right done once I define the
`per-file-class' in .emacs.

Regards,
Wolfkin

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# #######################################################

#+NAME: setup
#+BEGIN_SRC emacs-lisp :results silent :exports none
(require 'org-latex)
(require 'org-export-latex)
(unless (find "per-file-class" org-export-latex-classes :key 'car :test 'equal)
(add-to-list 'org-export-latex-classes
	     '("per-file-class"
	       "\\documentclass{scrartcl}"
	       ("\\section{%s}" . "\\section*{%s}")
	       ("\\subsection{%s}" . "\\subsection*{%s}")
	       ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
	       ("\\paragraph{%s}" . "\\paragraph*{%s}"))))
#+END_SRC

# #######################################################

#+TITLE:	The Nature of Lisp

#+AUTHOR:	Coffeemug
#+EMAIL:	coffeemug@gmail.com
#+DATE:		Monday, May 8, 2006

#+DESCRIPTION:	
#+KEYWORDS:	
#+LANGUAGE:	en
#+OPTIONS:	H:3 num:t toc:t \n:nil @:t ::t |:t ^:{} -:t f:t *:t <:t
#+OPTIONS:	TeX:t LaTeX:t skip:nil d:nil todo:t pri:nil tags:not-in-toc
#+INFOJS_OPT:	view:nil toc:t ltoc:t mouse:underline buttons:0 path:http://orgmode.org/org-info.js

#+EXPORT_SELECT_TAGS: export
#+EXPORT_EXCLUDE_TAGS: noexport

# #######################################################

#+LATEX_CLASS: per-file-class

#+LaTeX_HEADER: \usepackage{geometry}
#+LaTeX_HEADER: \geometry{left=1.5in,right=1.5in,top=1.5in,bottom=1.5in}

#+LaTeX_HEADER: \usepackage{indentfirst}
#+LaTeX_HEADER: \linespread{1.3}

# #+LaTeX_HEADER: \usepackage{CJK}
# #+LaTeX_HEADER: \begin{CJK}{UTF8}{gbsn}

# #######################################################

* Introduction

When I first stumbled into Lisp advocacy on various corners of the web I
was already an experienced programmer. At that point I had grokked what
seemed at the time a wide range of programming languages. I was proud to
have the usual suspects (C++, Java, C#, etc.) on my service record and
was under impression that I knew everything there is to know about
programming languages. I couldn't have possibly been more wrong.

My initial attempt to learn Lisp came to a crashing halt as soon as I
saw some sample code. I suppose the same thought ran through my mind
that ran through thousands of other minds who were ever in my shoes:
"Why on Earth would anyone want to use a language with such horrific
syntax?!" I couldn't be bothered to learn a language if its creators
couldn't be bothered to give it a pleasant syntax. After all, I was
almost blinded by the infamous Lisp parentheses!

The moment I regained my sight I communicated my frustrations to some
members of the Lisp sect. Almost immediately I was bombarded by a
standard set of responses: Lisp's parentheses are only a superficial
matter, Lisp has a huge benefit of code and data being expressed in the
same manner (which, obviously, is a huge improvement over XML), Lisp has
tremendously powerful metaprogramming facilities that allow programs to
write code and modify themselves, Lisp allows for creation of
mini-languages specific to the problem at hand, Lisp blurs the
distinction between run time and compile time, Lisp, Lisp, Lisp... The
list was very impressive. Needless to say none of it made sense. Nobody
could illustrate the usefulness of these features with specific examples
because these techniques are supposedly only useful in large software
systems. After many hours of debating that conventional programming
languages do the job just fine, I gave up. I wasn't about to invest
months into learning a language with a terrible syntax in order to
understand obscure features that had no useful examples. My time has not
yet come.

For many months the Lisp advocates pressed on. I was baffled. Many
extremely intelligent people I knew and had much respect for were
praising Lisp with almost religious dedication. There had to be
something there, something I couldn't afford not to get my hands on!
Eventually my thirst for knowledge won me over. I took the plunge, bit
the bullet, got my hands dirty, and began months of mind bending
exercises. It was a journey on an endless lake of frustration. I turned
my mind inside out, rinsed it, and put it back in place. I went through
seven rings of hell and came back. And then I got it.

The enlightenment came instantaneously. One moment I understood nothing,
and the next moment everything clicked into place. I've achieved
nirvana. Dozens of times I heard Eric Raymond's statement quoted by
different people: "Lisp is worth learning for the profound enlightenment
experience you will have when you finally get it; that experience will
make you a better programmer for the rest of your days, even if you
never actually use Lisp itself a lot." I never understood this
statement. I never believed it could be true. And finally, after all the
pain, it made sense! There was more truth to it than I ever could have
imagined. I've achieved an almost divine state of mind, an instantaneous
enlightenment experience that turned my view of computer science on its
head in less than a single second.

That very second I became a member of the Lisp cult. I felt something a
ninjitsu master must feel: I had to spread my newfound knowledge to at
least ten lost souls in the course of my lifetime. I took the usual
path. I was rehashing the same arguments that were given to me for years
(only now they actually made sense!), hoping to convert unsuspecting
bystanders. It didn't work. My persistence sparked a few people's
interest but their curiosity dwindled at the mere sight of sample Lisp
code. Perhaps years of advocacy would forge a few new Lispers, but I
wasn't satisfied. There had to be a better way.

I gave the matter careful thought. Is there something inherently hard
about Lisp that prevents very intelligent, experienced programmers from
understanding it? No, there isn't. After all, I got it, and if I can do
it, anybody can. Then what is it that makes Lisp so hard to understand?
The answer, as such things usually do, came unexpectedly. Of course!
Teaching anybody anything involves building advanced concepts on top of
concepts they already understand! If the process is made interesting and
the matter is explained properly the new concepts become as intuitive as
the original building blocks that aided their understanding. That was
the problem! Metaprogramming, code and data in one representation,
self-modifying programs, domain specific mini-languages, none of the
explanations for these concepts referenced familiar territory. How could
I expect anyone to understand them! No wonder people wanted specific
examples. I could as well have been speaking in Martian!

I shared my ideas with fellow Lispers. "Well, of course these concepts
aren't explained in terms of familiar territory", they said. "They are
so different, they're unlike anything these people have learned before."
This was a poor excuse. "I do not believe this to be true", I said. The
response was unanimous: "Why don't you give it a try?" So I did. This
article is a product of my efforts. It is my attempt to explain Lisp in
familiar, intuitive concepts. I urge brave souls to read on. Grab your
favorite drink. Take a deep breath. Prepare to be blown away. Oh, and
may the Force be with you.

* XML Reloaded

A thousand mile journey starts with a single step. A journey to
enlightenment is no exception and our first step just happens to be XML.
What more could possibly be said about XML that hasn't already been
said? It turns out, quite a bit. While there's nothing particularly
interesting about XML itself, its relationship to Lisp is fascinating.
XML is the all too familiar concept that Lisp advocates need so much. It
is our bridge to conveying understanding to regular programmers. So
let's revive the dead horse, take out the stick, and venture into XML
wilderness that no one dared venture into before us. It's time to see
the all too familiar moon from the other side.

Superficially XML is nothing more than a standardized syntax used to
express arbitrary hierarchical data in human readable form. To-do lists,
web pages, medical records, auto insurance claims, configuration files
are all examples of potential XML use. Let's use a simple to-do list as
an example (in a couple of sections you'll see it in a whole new light):

#+BEGIN_EXAMPLE
    <todo name="housework">
        <item priority="high">Clean the house.</item>
        <item priority="medium">Wash the dishes.</item>
        <item priority="medium">Buy more soap.</item>
    </todo>
#+END_EXAMPLE

What happens if we unleash our favorite XML parser on this to-do list?
Once the data is parsed, how is it represented in memory? The most
natural representation is, of course, a tree - a perfect data structure
for hierarchical data. After all is said and done, XML is really just a
tree serialized to a human readable form. Anything that can be
represented in a tree can be represented in XML and vice versa. I hope
you understand this idea. It's very important for what's coming next.

Let's take this a little further. What other type of data is often
represented as a tree? At this point the list is as good as infinite so
I'll give you a hint at what I'm getting at - try to remember your old
compiler course. If you have a vague recollection that source code is
stored in a tree after it's parsed, you're on the right track. Any
compiler inevitably parses the source code into an abstract syntax tree.
This isn't surprising since source code is hierarchical: functions
contain arguments and blocks of code. Blocks of code contain expressions
and statements. Expressions contain variables and operators. And so it
goes.

Let's apply our corollary that any tree can easily be serialized into
XML to this idea. If all source code is eventually represented as a
tree, and any tree can be serialized into XML, then all source code can
be converted to XML, right? Let's illustrate this interesting property
by a simple example. Consider the function below:

#+BEGIN_EXAMPLE
                   
    int add(int arg1, int arg2)
    {
        return arg1 + arg2;
    }
#+END_EXAMPLE

Can you convert this function definition to its XML equivalent? Turns
out, it's reasonably simple. Naturally there are many ways to do this.
Here is one way the resulting XML can look like:

#+BEGIN_EXAMPLE
    <define-function return-type="int" name="add">
        <arguments>
            <argument type="int">arg1</argument>
            <argument type="int">arg2</argument>
        </arguments>
        <body>
            <return>
                <add value1="arg1" value2="arg2" />
            </return>
        </body>
    </define>
#+END_EXAMPLE

We can go through this relatively simple exercise with any language. We
can turn any source code into XML, and we can transform the resulting
XML back to original source code. We can write a converter that turns
Java into XML and a converter that turns XML back to Java. We could do
the same for C++. (In case you're wondering if anyone is crazy enough to
do it, take a look at [[http://www.gccxml.org][GCC-XML]]). Furthermore,
for languages that share common features but use different syntax (which
to some extent is true about most mainstream languages) we could convert
source code from one language to another using XML as an intermediary
representation. We could use our Java2XML converter to convert a Java
program to XML. We could then run an XML2CPP converter on the resulting
XML and turn it into C++ code. With any luck (if we avoid using features
of Java that don't exist in C++) we'll get a working C++ program. Neat,
eh?

All this effectively means that we can use XML for generic storage of
source code. We'd be able to create a whole class of programming
languages that use uniform syntax, as well as write transformers that
convert existing source code to XML. If we were to actually adopt this
idea, compilers for different languages wouldn't need to implement
parsers for their specific grammars - they'd simply use an XML parser to
turn XML directly into an abstract syntax tree.

By now you're probably wondering why I've embarked on the XML crusade
and what it has to do with Lisp (after all, Lisp was created about
thirty years before XML). I promise that everything will become clear
soon enough. But before we take our second step, let's go through a
small philosophical exercise. Take a good look at the XML version of our
"add" function above. How would you classify it? Is it data or code? If
you think about it for a moment you'll realize that there are good
reasons to put this XML snippet into both categories. It's XML and it's
just information encoded in a standardized format. We've already
determined that it can be generated from a tree data structure in memory
(that's effectively what GCC-XML does). It's lying around in a file with
no apparent way to execute it. We can parse it into a tree of XML nodes
and do various transformations on it. It's data. But wait a moment! When
all is said and done it's the same "add" function written with a
different syntax, right? Once parsed, its tree could be fed into a
compiler and we could execute it. We could easily write a small
interpreter for this XML code and we could execute it directly.
Alternatively, we could transform it into Java or C++ code, compile it,
and run it. It's code.

So, where are we? Looks like we've just arrived to an interesting point.
A concept that has traditionally been so hard to understand is now
amazingly simple and intuitive. Code is also always data! Does it mean
that data is also always code? As crazy as this sounds this very well
might be the case. Remember how I promised that you'll see our to-do
list in a whole new light? Let me reiterate on that promise. But we
aren't ready to discuss this just yet. For now let's continue walking
down our path.

A little earlier I mentioned that we could easily write an interpreter
to execute our XML snippet of the add function. Of course this sounds
like a purely theoretical exercise. Who in their right mind would want
to do that for practical purposes? Well, it turns out quite a few people
would disagree. You've likely encountered and used their work at least
once in your career, too. Do I have you out on the edge of your seat? If
so, let's move on!

* Ant Reloaded

Now that we've made the trip to the dark side of the moon, let's not
leave quite yet. We may still learn something by exploring it a little
more, so let's take another step. We begin by closing our eyes and
remembering a cold rainy night in the winter of 2000. A prominent
developer by the name of James Duncan Davidson[fn:1] was
hacking his way through [[http://tomcat.apache.org/][Tomcat]] servlet
container. As the time came to build the changes he carefully saved all
his files and ran /make/. Errors. Lots of errors. Something was wrong.
After careful examination James exclaimed: "Is my command not executing
because I have a space in front of my tab?!" Indeed, this was the
problem. Again. James has had enough. He could sense the full moon
through the clouds and it made him adventurous. He created a fresh Java
project and quickly hacked together a simple but surprisingly useful
utility. This spark of genius used Java property files for information
on how to build the project. James could now write the equivalent of the
makefile in a nice format without worrying about the damned spaces ever
again. His utility did all the hard work by interpreting the property
file and taking appropriate actions to build the project. It was neat.
Another Neat Tool. [[http://ant.apache.org/][Ant]].

After using Ant to build Tomcat for a few months it became clear that
Java property files are not sufficient to express complicated build
instructions. Files needed to be checked out, copied, compiled, sent to
another machine, and unit tested. In case of failure e-mails needed to
be sent out to appropriate people. In case of success "Bad to the Bone"
needed to be played at the highest possible volume. At the end of the
track volume had to be restored to its original level. Yes, Java
property files didn't cut it anymore. James needed a more flexible
solution. He didn't feel like writing his own parser (especially since
he wanted an industry standard solution). XML seemed like a reasonable
alternative. In a couple of days Ant was ported to XML. It was the best
thing since sliced bread.

So how does Ant work? It's pretty simple. It takes an XML file with
specific build instructions (you decide if they're data or code) and
interprets them by running specialized Java code for each XML element.
It's actually much simpler than it sounds. A simple XML instruction like
the one below causes a Java class with an equivalent name to be loaded
and its code to be executed.

#+BEGIN_EXAMPLE
    <copy todir="../new/dir">
        <fileset dir="src_dir"/>
    </copy>
#+END_EXAMPLE

The snippet above copies a source directory to a destination directory.
Ant locates a "copy" task (a Java class, really), sets appropriate
parameters (todir and fileset) by calling appropriate Java methods and
then executes the task. Ant comes with a set of core tasks and anyone
can extend it with tasks of their own simply by writing Java classes
that follow certain conventions. Ant finds these classes and executes
them whenever XML elements with appropriate names are encountered.
Pretty simple. Effectively Ant accomplishes what we were talking about
in the previous section: it acts as an interpreter for a language that
uses XML as its syntax by translating XML elements to appropriate Java
instructions. We could write an "add" task and have Ant execute it when
it encounters the XML snippet for addition presented in the previous
section! Considering that Ant is an extremely popular project, the ideas
presented in the previous section start looking more sane. After all,
they're being used every day in what probably amounts to thousands of
companies!

So far I've said nothing about why Ant actually goes through all the
trouble of interpreting XML. Don't try to look for the answer on its
website either - you'll find nothing of value. Nothing relevant to our
discussion, anyway. Let's take another step. It's time to find out why.

* Why XML?

Sometimes right decisions are made without full conscious understanding
of all the issues involved. I'm not sure if James knew why he chose XML
- it was likely a subconscious decision. At the very least, the reasons
I saw on Ant's website for using XML are all the wrong reasons. It
appears that the main concerns revolved around portability and
extensibility. I fail to see how XML helps advance these goals in Ant's
case. What is the advantage of using interpreted XML over simple Java
source code? Why not create a set of classes with a nice API for
commonly used tasks (copying directories, compiling, etc.) and using
those directly from Java source code? This would run on every platform
that runs Java (which Ant requires anyway), it's infinitely extensible,
and it has the benefit of having a more pleasant, familiar syntax. So
why XML? Can we find a good reason for using it?

It turns out that we can (although as I mentioned earlier I'm not sure
if James was consciously aware of it). XML has the property of being far
more flexible in terms of introduction of semantic constructs than Java
could ever hope to be. Don't worry, I'm not falling into the trap of
using big words to describe incomprehensible concepts. This is actually
a relatively simple idea, though it may take some effort to explain.
Buckle your seat-belt. We're about to make a giant leap towards
achieving nirvana.

How can we represent 'copy' example above in Java code? Here's one way
to do it:

#+BEGIN_EXAMPLE
    CopyTask copy = new CopyTask();
    Fileset fileset = new Fileset();

    fileset.setDir("src_dir");
    copy.setToDir("../new/dir");
    copy.setFileset(fileset);

    copy.execute();
#+END_EXAMPLE

The code is almost the same, albeit a little longer than the original
XML. So what's different? The answer is that the XML snippet introduces
a special semantic construct for copying. If we could do it in Java it
would look like this:

#+BEGIN_EXAMPLE
           
    copy("../new/dir")
    {
        fileset("src_dir");
    }
#+END_EXAMPLE

Can you see the difference? The code above (if it were possible in Java)
is a special operator for copying files - similar to a /for/ loop or a
new /foreach/ construct introduced in Java 5. If we had an automatic
converter from XML to Java it would likely produce the above gibberish.
The reason for this is that Java's accepted syntax tree grammar is fixed
by the language specification - we have no way of modifying it. We can
add packages, classes, methods, but we cannot extend Java to make
addition of new operators possible. Yet we can do it to our heart's
content in XML - its syntax tree isn't restricted by anything except our
interpreter! If the idea is still unclear, consider introducing a
special operator 'unless' to Java:

#+BEGIN_EXAMPLE
                   
    unless(someObject.canFly())
    {
        someObject.transportByGround();
    }
#+END_EXAMPLE

In the previous two examples we extend the Java language to introduce an
operator for copying files and a conditional operator /unless/. We would
do this by modifying the abstract syntax tree grammar that Java compiler
accepts. Naturally we cannot do it with standard Java facilities, but we
can easily do it in XML. Because our XML interpreter parses the abstract
syntax tree that results from it, we can extend it to include any
operator we like.

For complex operators this ability provides tremendous benefits. Can you
imagine writing special operators for checking out source code,
compiling files, running unit testing, sending email? Try to come up
with some. If you're dealing with a specialized problem (in our case
it's building projects) these operators can do wonders to decrease the
amount of code you have to type and to increase clarity and code reuse.
Interpreted XML makes this extremely easy to accomplish because it's a
simple data file that stores hierarchical data. We do not have this
option in Java because it's hierarchical structure is fixed (as you will
soon find out, we do have this option in Lisp). Perhaps this is one of
the reasons why Ant is so successful?

I urge you to take a look at recent evolution of Java and C# (especially
the recently released specification for C# 3.0). The languages are being
evolved by abstracting away commonly used functionality and adding it in
the form of operators. New C# operators for built-in queries is one
example. This is accomplished by relatively traditional means: language
creators modify the accepted abstract syntax tree and add
implementations of certain features. Imagine the possibilities if the
programmer could modify the abstract syntax tree himself! Whole new
sub-languages could be built for specialized domains (for example a
language for building projects, like Ant). Can you come up with other
examples? Think about these concepts for a bit, but don't worry about
them too much. We'll come back to these issues after introducing a few
more ideas. By then things will be a little more clear.

* Almost Lisp

Let's forget about the operator business for the moment and try to
expand our horizons beyond the constraints of Ant's design. I mentioned
earlier that Ant can be extended by writing conventional Java classes.
Ant interpreter then attempts to match XML elements to appropriately
named Java classes and if the match is found the task is executed. An
interesting question begs to be asked. Why not extend Ant in Ant itself?
After all, core tasks contain a lot of conventional programming language
constructs ('if' being a perfect example). If Ant provided constructs to
develop tasks in Ant itself we'd reach a higher degree of portability.
We'd be dependent on a core set of tasks (a standard library, if you
will) and we wouldn't care if Java runtime is present: the core set
could be implemented in anything. The rest of the tasks would be built
on top of the core using Ant-XML itself. Ant would then become a
generic, extensible, XML-based programming language. Consider the
possibilities:

#+BEGIN_EXAMPLE
    <task name="Test">
        <echo message="Hello World!"/>
    </task>
    <Test />
#+END_EXAMPLE

If ant supported the "task" construct, the example above would print
"Hello World!". In fact, we could write a "task" task in Java and make
Ant able to extend itself using Ant-XML! Ant would then be able to build
more complicated primitives on top of simple ones, just like any other
programming language! This is an example of "XML" based programming
language we were talking about in the beginning of this tutorial. Not
very useful (can you tell why?) but pretty damn cool.

By the way, take a look at our 'Test' task once again. Congratulations.
You're looking at Lisp code. What on Earth am I talking about? It
doesn't look anything like Lisp? Don't worry, we'll fix that in a bit.
Confused? Good. Let's clear it all up!

* A Better XML

I mentioned in the previous section that self-extending Ant wouldn't be
very useful. The reason for that is XML's verbosity. It's not too bad
for data files but the moment you try writing reasonably complex code
the amount of typing you have to do quickly starts to get in the way and
progresses to becoming unusable for any real project. Have you ever
tried writing Ant build scripts? I have, and once they get complex
enough having to do it in XML becomes really annoying. Imagine having to
type almost everything in Java twice because you have to close every
element. Wouldn't that drive you nuts?

The solution to this problem involves using a less verbose alternative
to XML. Remember, XML is just a format for representing hierarchical
data. We don't have to use XML's angle brackets to serialize trees. We
could come up with many other formats. One such format (incidentally,
the one Lisp uses) is called an s-expression. S-expressions accomplish
the same goals as XML. They're just a lot less verbose, which makes them
much better suited for typing code. I will explain s-expressions in a
little while, but before I do I have to clear up a few things about XML.
Let's consider our XML example for copying files:

#+BEGIN_EXAMPLE
    <copy todir="../new/dir">
        <fileset dir="src_dir"/>
    </copy>
#+END_EXAMPLE

Think of what the parse tree of this snippet would look like in memory.
We'd have a 'copy' node that contains a fileset node. But what about
attributes? How do they fit into our picture? If you've ever used XML to
describe data and wondered whether you should use an element or an
attribute, you're not alone. Nobody can really figure this out and doing
it right tends to be black magic rather than science. The reason for
that is that attributes are really subsets of elements. Anything
attributes can do, elements can do as well. The reason attributes were
introduced is to curb XML's verbosity. Take a look at another version of
our 'copy' snippet:

#+BEGIN_EXAMPLE
    <copy>
        <todir>../new/dir</todir>
        <fileset>
            <dir>src_dir</dir>
        </fileset>
    </copy>
#+END_EXAMPLE

The two snippets hold exactly the same information. However, we use
attributes to avoid typing the same thing more than once. Imagine if
attributes weren't part of XML specification. Writing anything in XML
would drive us nuts!

Now that we got attributes out of the way, let's look at s-expressions.
The reason we took this detour is that s-expressions do not have
attributes. Because they're a lot less verbose, attributes are simply
unnecessary. This is one thing we need to keep in mind when transforming
XML to s-expressions. Let's take a look at an example. We could
translate above snippet to s-expressions like this:

#+BEGIN_EXAMPLE
    (copy
        (todir "../new/dir")
        (fileset (dir "src_dir")))
#+END_EXAMPLE

Take a good look at this representation. What's different? Angle
brackets seem to be replaced by parentheses. Instead of enclosing each
element into a pair of parentheses and then closing each element with a
"(/element)" we simply skip the second parenthesis in "(element" and
proceed. The element is then closed like this: ")". That's it! The
translation is natural and very simple. It's also a lot easier to type.
Do parentheses blind first time users? Maybe, but now that we're
understand the reasoning behind them they're a lot easier to handle. At
the very least they're better than arthritis inducing verbosity of XML.
After you get used to s-expressions writing code in them is not only
doable but very pleasant. And they provide all the benefits of writing
code in XML (many of which we're yet to explore). Let's take a look at
our 'task' code in something that looks a lot more like lisp:

#+BEGIN_EXAMPLE
    (task (name "Test")
        (echo (message "Hello World!")))

    (Test)
#+END_EXAMPLE

S-expressions are called lists in Lisp lingo. Consider our 'task'
element above. If we rewrite it without a line break and with comas
instead of spaces it's starting to look surprisingly like a list of
elements and other lists (the formatting is added to make it easier to
see nested lists):

#+BEGIN_EXAMPLE
    (task, (name, "test"), (echo, (message, "Hello World!")))
#+END_EXAMPLE

We could do the same with XML. Of course the line above isn't really a
list, it's a tree, just like its XML-alternative. Don't let references
to lists confuse you, it's just that lists that contain other lists and
trees are effectively the same thing. Lisp may stand for List
Processing, but it's really tree processing - no different than
processing XML nodes.

Whew. After much rambling we finally got to something that looks like
Lisp (and is Lisp, really). By now the mysterious Lisp parentheses as
well as some claims made by Lisp advocates should become more clear. But
we still have a lot of ground to cover. Ready? Let's move on!

* C Macros Reloaded

By now you must be tired of all the XML talk. I'm tired of it as well.
It's time to take a break from all the trees, s-expressions, and Ant
business. Instead, let's go back to every programmer's roots. It's time
to talk about C preprocessor. What's C got to do with anything, I hear
you ask? Well, we now know enough to get into metaprogramming and
discuss code that writes other code. Understanding this tends to be hard
since all tutorials discuss it in terms of languages that you don't
know. But there is nothing hard about the concept. I believe that a
metaprogramming discussion based on C will make the whole thing much
easier to understand. So, let's see (pun intended).

Why would anyone want to write a program that writes programs? How can
we use something like this in the real world? What on Earth is
metaprogramming, anyway? You already know all the answers, you just
don't know it yet. In order to unlock the hidden vault of divine
knowledge let's consider a rather mundane task of simple database access
from code. We've all been there. Writing SQL queries all over the code
to modify data within tables turns into repetitive hell soon enough.
Even with the new C# 3.0 LINQ stuff this is a huge pain. Writing a full
SQL query (albeit with a nice built in syntax) to get someone's name or
to modify someone's address isn't exactly a programmer's idea of
comfort. What do we do to solve these problems? Enter data access
layers.

The idea is simple enough. You abstract database access (at least
trivial queries, anyway) by creating a set of classes that mirror the
tables in the database and use accessor methods to execute actual
queries. This simplifies development tremendously - instead of writing
SQL queries we make simple method calls (or property assignments,
depending on your language of choice). Anyone who has ever used even the
simplest of data access layers knows how much time it can save. Of
course anyone who has ever written one knows how much time it can kill -
writing a set of classes that mirror tables and convert accessors to SQL
queries takes a considerable chunk of time. This seems especially silly
since most of the work is manual: once you figure out the design and
develop a template for your typical data access class you don't need to
do any thinking. You just write code based on the same template over and
over and over and over again. Many people figured out that there is a
better way - there are plenty of tools that connect to the database,
grab the schema, and write code for you based on a predefined (or a
custom) template.

Anyone who has ever used such a tool knows what an amazing time saver it
can be. In a few clicks you connect the tool to the database, get it to
generate the data access layer source code, add the files to your
project and voilà - ten minutes worth of work do a better job than
hundreds of man-hours that were required previously. What happens if
your database schema changes? Well, you just have to go through this
short process again. Of course some of the best tools let you automate
this - you simply add them as a part of your build step and every time
you compile your project everything is done for you automatically. This
is perfect! You barely have to do anything at all. If the schema ever
changes your data access layer code updates automatically at compile
time and any obsolete access in your code will result in compiler
errors!

Data access layers are one good example, but there are plenty of others.
From boilerplate GUI code, to web code, to COM and CORBA stubs, to MFC
and ATL, - there are plenty of examples where the same code is written
over and over again. Since writing this code is a task that can be
automated completely and a programmer's time is far more expensive than
CPU time, plenty of tools have been created that generate this
boilerplate code automatically. What are these tools, exactly? Well,
they are programs that write programs. They perform a simple task that
has a mysterious name of metaprogramming. That's all there is to it.

We could create and use such tools in millions of scenarios but more
often than not we don't. What it boils down to is a subconscious
calculation - is it worth it for me to create a separate project, write
a whole tool to generate something, and then use it, if I only have to
write these very similar pieces about seven times? Of course not. Data
access layers and COM stubs are written hundreds, thousands of times.
This is why there are tools for them. For similar pieces of code that
repeat only a few times, or even a few dozen times, writing code
generation tools isn't even considered. The trouble to create such a
tool more often than not far outweighs the benefit of using one. If only
creating such tools was much easier, we could use them more often, and
perhaps save many hours of our time. Let's see if we can accomplish this
in a reasonable manner.

Surprisingly C preprocessor comes to the rescue. We've all used it in C
and C++. On occasion we all wish Java had it. We use it to execute
simple instructions at compile time to make small changes to our code
(like selectively removing debug statements). Let's look at a quick
example:

#+BEGIN_EXAMPLE
    #define triple(X)    X + X + X
#+END_EXAMPLE

What does this line do? It's a simple instruction written in the
preprocessor language that instructs it to replace all instances of
/triple(X)/ with /X + X + X/. For example all instances of '/triple(5)/'
will be replaced with '/5 + 5 + 5/' and the resulting code will be
compiled by the C compiler. We're really doing a very primitive version
of code generation here. If only C preprocessor was a little more
powerful and included ways to connect to the database and a few more
simple constructs, we could use it to develop our data access layer
right there, from within our program! Consider the following example
that uses an imaginary extension of the C preprocessor:

#+BEGIN_EXAMPLE
    #get-db-schema("127.0.0.1, un, pwd");
    #iterate-through-tables
    #for-each-table
        class #table-name
        {
        };
    #end-for-each
#+END_EXAMPLE

We've just connected to the database schema, iterated through all the
tables, and created an empty class for each. All in a couple of lines
right within our source code! Now every time we recompile the file where
above code appears we'll get a freshly built set of classes that
automatically update based on the schema. With a little imagination you
can see how we could build a full data access layer straight from within
our program, without the use of any external tools! Of course this has a
certain disadvantage (aside from the fact that such an advanced version
of C preprocessor doesn't exist) - we'd have to learn a whole new
"compile-time language" to do this sort of work. For complex code
generation this language would have to be very complex as well, it would
have to support many libraries and language constructs. For example, if
our generated code depended on some file located at some ftp server the
preprocessor would have to be able to connect to ftp. It's a shame to
create and learn a new language just to do this. Especially since there
are so many nice languages already out there. Of course if we add a
little creativity we can easily avoid this pitfall.

Why not replace the preprocessor language with C/C++ itself? We'd have
full power of the language at compile time and we'd only need to learn a
few simple directives to differentiate between compile time and runtime
code!

#+BEGIN_EXAMPLE
    <%
        cout << "Enter a number: ";
        cin >> n;
    %>
    for(int i = 0; i < <%= n %>; i++)
    {
        cout << "hello" << endl;
    }
#+END_EXAMPLE

Can you see what happens here? Everything that's between <% and %> tags
runs when the program is compiled. Anything outside of these tags is
normal code. In the example above you'd start compiling your program in
the development environment. The code between the tags would be compiled
and then ran. You'd get a prompt to enter a number. You'd enter one and
it would be placed inside the for loop. The for loop would then be
compiled as usual and you'd be able to execute it. For example, if you'd
enter 5 during the compilation of your program, the resulting code would
look like this:

#+BEGIN_EXAMPLE
    for(int i = 0; i < 5; i++)
    {
        cout << "hello" << endl;
    }
#+END_EXAMPLE

Simple and effective. No need for a special preprocessor language. We
get full power of our host language (in this case C/C++) at compile
time. We could easily connect to a database and generate our data access
layer source code at compile time in the same way JSP or ASP generate
HTML! Creating such tools would also be tremendously quick and simple.
We'd never have to create new projects with specialized GUIs. We could
inline our tools right into our programs. We wouldn't have to worry
about whether writing such tools is worth it because writing them would
be so fast - we could save tremendous amounts of time by creating simple
bits of code that do mundane code generation for us!

* Hello, Lisp!

Everything we've learned about Lisp so far can be summarized by a single
statement: Lisp is executable XML with a friendlier syntax. We haven't
said a single word about how Lisp actually operates. It's time to fill
this gap[fn:2].

Lisp has a number of built in data types. Integers and strings, for
example, aren't much different from what you're used to. The meaning of
/71/ or /"hello"/ is roughly the same in Lisp as in C++ or Java. What is
of more interest to us are /symbols/, /lists/, and /functions/. I will
spend the rest of this section describing these data types as well as
how a Lisp environment compiles and executes the source code you type
into it (this is called /evaluation/ in Lisp lingo). Getting through
this section in one piece is important for understanding true potential
of Lisp's metaprogramming, the unity of code and data, and the notion of
domain specific languages. Don't think of this section as a chore
though, I'll try to make it fun and accessible. Hopefully you can pick
up a few interesting ideas on the way. Ok. Let's start with Lisp's
symbols.

A symbol in Lisp is roughly equivalent to C++ or Java's notion of an
identifier. It's a name you can use to access a variable (like
/currentTime/, /arrayCount/, /n/, etc.) The difference is that a symbol
in Lisp is a lot more liberal than its mainstream identifier
alternative. In C++ or Java you're limited to alphanumeric characters
and an underscore. In Lisp, you are not. For example /+/ is a valid
symbol. So is /-/, /=/, /hello-world/, /hello+world/, /*/, etc. (you can
find the exact definition of valid Lisp symbols online). You can assign
to these symbols any data-type you like. Let's ignore Lisp syntax and
use pseudo-code for now. Assume that a function /set/ assigns some value
to a symbol (like /=/ does in Java or C++). The following are all valid
examples:

#+BEGIN_EXAMPLE
    set(test, 5)            // symbol 'test' will equal an integer 5
    set(=, 5)               // symbol '=' will equal an integer 5
    set(test, "hello")      // symbol 'test' will equal a string "hello"
    set(test, =)            // at this point symbol '=' is equal to 5
                            // therefore symbol 'test' will equal to 5
    set(*, "hello")         // symbol '*' will equal a string "hello"
#+END_EXAMPLE

At this point something must smell wrong. If we can assign strings and
integers to symbols like /*/, how does Lisp do multiplication? After
all, /*/ means multiply, right? The answer is pretty simple. Functions
in Lisp aren't special. There is a data-type, function, just like
integer and string, that you assign to symbols. A multiplication
function is built into Lisp and is assigned to a symbol /*/. You can
reassign a different value to /*/ and you'd lose the multiplication
function. Or you can store the value of the function in some other
variable. Again, using pseudo-code:

#+BEGIN_EXAMPLE
    *(3, 4)                 // multiplies 3 by 4, resulting in 12
    set(temp, *)            // symbol '*' is equal to the multiply function
                            // so temp will equal to the multiply function
    set(*, 3)               // sets symbol '*' to equal to 3
    *(3, 4)                 // error, symbol '*' no longer equals to a function
                            // it's equal to 3
    temp(3, 4)              // temp equals to a multiply function
                            // so Lisp multiplies 3 by 4 resulting in 12
    set(*, temp)            // symbol '*' equals multiply function again
    *(3, 4)                 // multiplies 3 by 4, resulting in 12
#+END_EXAMPLE

You can even do wacky stuff like reassigning plus to minus:

#+BEGIN_EXAMPLE
    set(+, -)               // the value of '-' is a built in minus function
                            // so now symbol '+' equals to a minus function
    +(5, 4)                 // since symbol '+' is equal to the minus function
                            // this results in 1
#+END_EXAMPLE

I've used functions quite liberally in these examples but I didn't
describe them yet. A function in Lisp is just a data-type like an
integer, a string, or a symbol. A function doesn't have a notion of a
name like in Java or C++. Instead, it stands on its own. Effectively it
is a pointer to a block of code along with some information (like a
number of parameters it accepts). You only give the function a name by
assigning it to a symbol, just like you assign an integer or a string.
You can create a function by using a built in function for creating
functions, assigned to a symbol 'fn'. Using pseudo-code:

#+BEGIN_EXAMPLE
    fn [a]
    {
        return *(a, 2);
    }
#+END_EXAMPLE

This returns a function that takes a single parameter named /'a'/ and
doubles it. Note that the function has no name but you can assign it to
a symbol:

#+BEGIN_EXAMPLE
    set(times-two, fn [a] { return *(a, 2); })
#+END_EXAMPLE

We can now call this function:

#+BEGIN_EXAMPLE
    times-two(5)             // returns 10
#+END_EXAMPLE

Now that we went over symbols and functions, what about lists? Well, you
already know a lot about them. Lists are simply pieces of XML written in
s-expression form. A list is specified by parentheses and contains Lisp
data-types (including other lists) separated by a space. For example
(this is real Lisp, note that we use semicolons for comments now):

#+BEGIN_EXAMPLE
    ()                      ; an empty list
    (1)                     ; a list with a single element, 1
    (1 "test")              ; a list with two elements
                            ; an integer 1 and a string "test"
    (test "hello")          ; a list with two elements
                            ; a symbol test and a string "hello"
    (test (1 2) "hello")    ; a list with three elements, a symbol test
                            ; a list of two integers 1 and 2
                            ; and a string "hello"
#+END_EXAMPLE

When a Lisp system encounters lists in the source code it acts exactly
like Ant does when it encounters XML - it attempts to execute them. In
fact, Lisp source code is only specified using lists, just like Ant
source code is only specified using XML. Lisp executes lists in the
following manner. The first element of the list is treated as the name
of a function. The rest of the elements are treated as functions
parameters. If one of the parameters is another list it is executed
using the same principles and the result is passed as a parameter to the
original function. That's it. We can write real code now:

#+BEGIN_EXAMPLE
    (* 3 4)                 ; equivalent to pseudo-code *(3, 4).
                            ; Symbol '*' is a function
                            ; 3 and 4 are its parameters.
                            ; Returns 12.
    (times-two 5)           ; returns 10
    (3 4)                   ; error: 3 is not a function
    (times-two)              ; error, times-two expects one parameter
    (times-two 3 4)          ; error, times-two expects one parameter
    (set + -)               ; sets symbol '+' to be equal to whatever symbol '-'
                            ; equals to, which is a minus function
    (+ 5 4)                 ; returns 1 since symbol '+' is now equal
                            ; to the minus function
    (* 3 (* 2 2))           ; multiplies 3 by the second parameter
                            ; (which is a function call that returns 4).
                            ; Returns 12.
#+END_EXAMPLE

Note that so far every list we've specified was treated by a Lisp system
as code. But how can we treat a list as data? Again, imagine an Ant task
that accepts XML as one of its parameters. In Lisp we do this using a
quote operator /'/ like so:

#+BEGIN_EXAMPLE
    (set test '(1 2))       ; test is equal to a list of two integers, 1 and 2
    (set test (1 2))        ; error, 1 is not a function
    (set test '(* 3 4))     ; sets test to a list of three elements,
                            ; a symbol *, an integer 3, and an integer 4
#+END_EXAMPLE

We can use a built in function /head/ to return the first element of the
list, and a built in function /tail/ to return the rest of the list's
elements:

#+BEGIN_EXAMPLE
    (head '(* 3 4))         ; returns a symbol '*'
    (tail '(* 3 4))         ; returns a list (3 4)
    (head (tail '( * 3 4))) ; (tail '(* 3 4)) returns a list (3 4)
                            ; and (head '(3 4)) returns 3.
    (head test)             ; test was set to a list in previous example
                            ; returns a symbol '*'
#+END_EXAMPLE

You can think of built in Lisp functions as you think of Ant tasks. The
difference is that we don't have to extend Lisp in another language
(although we can), we can extend it in Lisp itself as we did with the
/times-two/ example. Lisp comes with a very compact set of built in
functions - the necessary minimum. The rest of the language is
implemented as a standard library in Lisp itself.

* Lisp Macros

So far we've looked at metaprogramming in terms of a simple templating
engine similar to JSP. We've done code generation using simple string
manipulations. This is generally how most code generation tools go about
doing this task. But we can do much better. To get on the right track,
let's start off with a question. How would we write a tool that
automatically generates Ant build scripts by looking at source files in
the directory structure?

We could take the easy way out and generate Ant XML by manipulating
strings. Of course a much more abstract, expressive and extensible way
is to work with XML processing libraries to generate XML nodes directly
in memory. The nodes can then be serialized to strings automatically.
Furthermore, our tool would be able to analyze and transform existing
Ant build scripts by loading them and dealing with the XML nodes
directly. We would abstract ourselves from strings and deal with higher
level concepts which let us get the job done faster and easier.

Of course we could write Ant tasks that allow dealing with XML
transformations and write our generation tool in Ant itself. Or we could
just use Lisp. As we saw earlier, a list is a built in Lisp data
structure and Lisp has a number of facilities for processing lists
quickly and effectively (/head/ and /tail/ being the simplest ones).
Additionally Lisp has no semantic constraints - you can have your code
(and data) have any structure you want.

Metaprogramming in Lisp is done using a construct called a "macro".
Let's try to develop a set of macros that transform data like, say, a
to-do list (surprised?), into a language for dealing with to-do lists.

Let's recall our to-do list example. The XML looks like this:

#+BEGIN_EXAMPLE
    <todo name="housework">
        <item priority="high">Clean the house.</item>
        <item priority="medium">Wash the dishes.</item>
        <item priority="medium">Buy more soap.</item>
    </todo>
#+END_EXAMPLE

The corresponding s-expression version looks like this:

#+BEGIN_EXAMPLE
    (todo "housework"
        (item (priority high) "Clean the house.")
        (item (priority medium) "Wash the dishes.")
        (item (priority medium) "Buy more soap."))
#+END_EXAMPLE

Suppose we're writing a to-do manager application. We keep our to-do
items serialized in a set of files and when the program starts up we
want to read them and display them to the user. How would we do this
with XML and some other language (say, Java)? We'd parse our XML files
with the to-do lists using some XML parser, write the code that walks
the XML tree and converts it to a Java data structure (because frankly,
processing DOM in Java is a pain in the neck), and then use this data
structure to display the data. Now, how would we do the same thing in
Lisp?

If we were to adopt the same approach we'd parse the files using Lisp
libraries responsible for parsing XML. The XML would then be presented
to us as a Lisp list (an s-expression) and we'd walk the list and
present relevant data to the user. Of course if we used Lisp it would
make sense to persist the data as s-expressions directly as there's no
reason to do an XML conversion. We wouldn't need special parsing
libraries since data persisted as a set of s-expressions is valid Lisp
and we could use Lisp compiler to parse it and store it in memory as a
Lisp list. Note that Lisp compiler (much like .NET compiler) is
available to a Lisp program at runtime.

But we can do better. Instead of writing code to walk the s-expression
that stores our data we could write a macro that allows us to treat data
as code! How do macros work? Pretty simple, really. Recall that a Lisp
function is called like this:

#+BEGIN_EXAMPLE
    (function-name arg1 arg2 arg3)
#+END_EXAMPLE

Where each argument is a valid Lisp expression that's evaluated and
passed to the function. For example if we replace /arg1/ above with /(+
4 5)/, it will be evaluated and /9/ would be passed to the function. A
macro works the same way as a function, except its arguments are not
evaluated.

#+BEGIN_EXAMPLE
    (macro-name (+ 4 5))
#+END_EXAMPLE

In this case, (+ 4 5) is not evaluated and is passed to the macro as a
list. The macro is then free to do what it likes with it, including
evaluating it. The return value of a macro is a Lisp list that's treated
as code. The original place with the macro is replaced with this code.
For example, we could define a macro plus that takes two arguments and
puts in the code that adds them.

What does it have to do with metaprogramming and our to-do list problem?
Well, for one, macros are little bits of code that generate code using a
list abstraction. Also, we could create macros named /to-do/ and /item/
that replace our data with whatever code we like, for instance code that
displays the item to the user.

What benefits does this approach offer? We don't have to walk the list.
The compiler will do it for us and will invoke appropriate macros. All
we need to do is create the macros that convert our data to appropriate
code!

For example, a macro similar to our /triple/ C macro we showed earlier
looks like this:

#+BEGIN_EXAMPLE
    (defmacro triple (x)
        '(+ ~x ~x ~x))
#+END_EXAMPLE

The quote prevents evaluation while the tilde allows it. Now every time
/triple/ is encountered in lisp code:

#+BEGIN_EXAMPLE
    (triple 4)
#+END_EXAMPLE

it is replaced with the following code:

#+BEGIN_EXAMPLE
    (+ 4 4 4)
#+END_EXAMPLE

We can create macros for our to-do list items that will get called by
lisp compiler and will transform the to-do list into code. Now our to-do
list will be treated as code and will be executed. Suppose all we want
to do is print it to standard output for the user to read:

#+BEGIN_EXAMPLE
    (defmacro item (priority note)
        '(block
             (print stdout tab "Priority: "
                 ~(head (tail priority)) endl)
             (print stdout tab "Note: " ~note endl endl)))
#+END_EXAMPLE

We've just created a very small and limited language for managing to-do
lists embedded in Lisp. Such languages are very specific to a particular
problem domain and are often referred to as domain specific languages or
/DSLs/.

* Domain Specific Languages

In this article we've already encountered two domain specific languages:
Ant (specific to dealing with project builds) and our unnamed
mini-language for dealing with to-do lists. The difference is that Ant
was written from scratch using XML, an XML parser, and Java while our
language is embedded into Lisp and is easily created within a couple of
minutes.

We've already discussed the benefits of DSLs, mainly why Ant is using
XML, not Java source code. Lisp lets us create as many DSLs as we need
for our problem. We can create domain specific languages for creating
web applications, writing massively multiplayer games, doing fixed
income trading, solving the protein folding problem, dealing with
transactions, etc. We can layer these languages on top of each other and
create a language for writing web-based trading applications by taking
advantage of our web application language and bond trading language.
Every day we'd reap the benefits of this approach, much like we reap the
benefits of Ant.

Using DSLs to solve problems results in much more compact, maintainable,
flexible programs. In a way we create them in Java by creating classes
that help us solve the problem. The difference is that Lisp allows us to
take this abstraction to the next level: we're not limited by Java's
parser. Think of writing build scripts in Java itself using some
supporting library. Compare it to using Ant. Now apply this same
comparison to every single problem you've ever worked on and you'll
begin to glimpse a small share of the benefits offered by Lisp.

* What's next?

Learning Lisp is an uphill battle. Even though in Computer Science terms
Lisp is an ancient language, few people to date figured out how to teach
it well enough to make it accessible. Despite great efforts by many Lisp
advocates, learning Lisp today is still hard. The good news is that this
won't remain the case forever since the amount of Lisp-related resources
is rapidly increasing. Time is on Lisp's side.

Lisp is a way to escape mediocrity and to get ahead of the pack.
Learning Lisp means you can get a better job today, because you can
impress any reasonably intelligent interviewer with fresh insight into
most aspects of software engineering. It also means you're likely to get
fired tomorrow because everyone is tired of you constantly mentioning
how much better the company could be doing if only its software was
written in Lisp. Is it worth the effort? Everyone who has ever learned
Lisp says yes. The choice, of course, remains yours.

* Comments?

Whew. That's enough. I've been writing this article, on and off, for
months. If you find it interesting, have any questions, comments, or
suggestions, please drop a note at
[[mailto:coffeemug@gmail.com][coffeemug@gmail.com]]. I'll be glad to
hear your feedback.

[fn:1]I have never met James, nor does he know about my existence. The
story is entirely fictional and is based on a few postings about Ant's
history I found on the internet.

[fn:2]Lisp has many different dialects (the most popular of which are
Common Lisp and Scheme). Each dialect deals with intricate details
differently yet shares the same set of basic principles. Since the goal
of this article is to give you an understanding of Lisp's principles I
will use Blaise for examples (which at the time of this writing is
vaporware). With some minor modifications these examples can be
translated to other Lisp dialects.


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: "No definition" for "per-file basis in a source code block" mode
  2013-04-15  8:34 "No definition" for "per-file basis in a source code block" mode Wolfkin Chiang
@ 2013-04-15 11:38 ` Suvayu Ali
  0 siblings, 0 replies; 3+ messages in thread
From: Suvayu Ali @ 2013-04-15 11:38 UTC (permalink / raw)
  To: emacs-orgmode

On Mon, Apr 15, 2013 at 04:34:57PM +0800, Wolfkin Chiang wrote:
> Hi, All,
> 
> While I try the "per-file basis in a source code block" mode,
> It tells me:
> No definition for class `per-file-class' in `org-export-latex-classes'
> Please help me to resolve it, thanks!

  (require 'org-latex)
  (require 'org-export-latex)

The above is incorrect.  It should be:

  (require 'ox-latex)

Hope this helps,

-- 
Suvayu

Open source is the future. It sets us free.

^ permalink raw reply	[flat|nested] 3+ messages in thread

* "No definition" for "per-file basis in a source code block" mode
@ 2013-04-08  5:18 Wolfkin Chiang
  0 siblings, 0 replies; 3+ messages in thread
From: Wolfkin Chiang @ 2013-04-08  5:18 UTC (permalink / raw)
  To: emacs-orgmode


[-- Attachment #1.1: Type: text/plain, Size: 1336 bytes --]

Hi, All,

While I try the "per-file basis in a source code block" mode,
It tells me:
No definition for class `per-file-class' in `org-export-latex-classes'

I command
$ emacs -D -nw --no-splash --batch --kill --file tt1.org --funcall
org-export-as-latex
And it tells me:
Loading 00debian-vars...
Loading /etc/emacs/site-start.d/50asymptote.el (source)...
Loading /etc/emacs/site-start.d/50dictionaries-common.el (source)...
Loading debian-ispell...
Loading /var/cache/dictionaries-common/emacsen-ispell-default.el (source)...
Loading /var/cache/dictionaries-common/emacsen-ispell-dicts.el (source)...
Loading /etc/emacs/site-start.d/50emacs-goodies-el.el (source)...
Loading /etc/emacs/site-start.d/50geiser.el (source)...
Loading /etc/emacs/site-start.d/50latex-cjk-common.el (source)...
Loading cjk-enc...
Loading /etc/emacs/site-start.d/50latex-cjk-thai.el (source)...
Loading /etc/emacs/site-start.d/50org-mode.el (source)...
Loading /etc/emacs/site-start.d/50python-docutils.el (source)...
Loading /etc/emacs/site-start.d/50thailatex.el (source)...
OVERVIEW
Exporting to LaTeX...
No definition for class `per-file-class' in `org-export-latex-classes'

And no positive response whill I try to move the source block at begin.
And it is true that this can be right done once I define the
`per-file-class' in .emacs.

Regards,
Wolfkin

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# #######################################################

#+TITLE:     迴歸“溫良恭儉讓”

#+AUTHOR:    茅于軾
#+EMAIL:     wolfkin.chiang@gmail.com

#+DESCRIPTION:
#+KEYWORDS:
#+LANGUAGE:  zh

#+OPTIONS:   H:3 num:t toc:t \n:nil @:t ::t |:t ^:{} -:t f:t *:t <:t
#+OPTIONS:   TeX:t LaTeX:xelatex skip:nil d:nil todo:t pri:nil tags:not-in-toc
#+INFOJS_OPT: view:nil toc:2 ltoc:t mouse:underline buttons:0 path:http://orgmode.org/org-info.js

#+EXPORT_SELECT_TAGS: export
#+EXPORT_EXCLUDE_TAGS: noexport

#+LINK_UP:
#+LINK_HOME:

# #######################################################

#+NAME: setup
#+BEGIN_SRC emacs-lisp :results silent :exports none
(require 'org-latex)
(require 'org-export-latex)
(unless (find "per-file-class" org-export-latex-classes :key 'car :test 'equal)
(add-to-list 'org-export-latex-classes
	     '("per-file-class"
	       "
\\documentclass{scrartcl}
[NO-DEFAULT-PACKAGES]
[EXTRA]

\\usepackage{hyperref}

\\usepackage[CJKnumber=true]{xeCJK}
\\setCJKmainfont{全字庫正楷體}
\\setCJKsansfont{全字庫正楷體}

\\usepackage{CJKnumb}
"
	       ("\\section{%s}" . "\\section*{%s}")
	       ("\\subsection{%s}" . "\\subsection*{%s}")
	       ("\\subsubsection{%s}" . "\\subsubsection*{%s}")
	       ("\\paragraph{%s}" . "\\paragraph*{%s}"))))
#+END_SRC

# #######################################################

#+LaTeX_CLASS: per-file-class
#+LaTeX_CLASS_OPTIONS: [10pt, a4paper]

#+LaTeX_HEADER: \usepackage{geometry}
#+LaTeX_HEADER: \geometry{left=1.5in,right=1.5in,top=1.5in,bottom=1.5in}

#+LaTeX_HEADER: \usepackage{indentfirst}
#+LaTeX_HEADER: \linespread{1.3}

# #######################################################

中國是禮儀之邦,有五千年的不間斷的文化傳統。這在世界上是獨一無二的。其所以中華民族能夠維繫五千年之久,一個重要原因是百姓之間的關係是良好的,是有利於社會和諧,健康發展的。人們之間遵從不彼此傷害,而且互敬互讓、禮貌相待的原則。如果我們提倡互相鬥爭,把鬥爭深入到每個家庭、學校、單位,中華民族早就自我滅亡了。幾千年來中國人遵循的規則就是“溫,良,恭,儉,讓”五個字。它非常恰當地規定了人與人相處的原則。一個具有這五字修養的人,是溫和的,善良的,對別人恭敬的,講究節約的,不事誇張的,而且是謙讓的,不爭先恐後的。如果我們周圍接觸到的人都具有這五字修養,我們一定生活在一個和平,友好的環境裏。不會有傷腦筋的爭端,更沒有對自己安全的威脅。

其實,這種講究人和人相處的道理,在各種不同的文明中都是存在的。比如在英國,人民講究紳士作風。所謂紳士作風和“溫良恭儉讓”差不多,不過更在乎外在的表現,不像我們所崇尚的更注重內在的修養。但不管是外在表現也好,內在修養也好,其結果都是一個和諧的人際關係,它保證了我們生活的安定、有秩序、不受傷害。

沒有了這五個字,會是什麼結果?看看文化革命的慘痛教訓。用暴力代替了溫和,用醜惡代替了善良,用蔑視代替了恭敬,用張揚代替了節儉,用鬥爭代替了謙讓。這是全民族的浩劫,是全社會痛苦的極大化。十年“文革”中斷了中華民族幾千年的優良傳統。“文革”後中國倒過來向西方學習人與人相處的規則。開始學習講“謝謝你”(thank you)“對不起”(sorry 或pardon me),“請原諒”(excuse me)。文革中從來不講“謝謝”,不講“對不起”,更沒人會講“請原諒”。儘管回過頭來學了西方,我們還遠遠沒有恢復到“文革”前,或解放前的人際關係。馬路上常常能看到人與人吵架,城管打人,張口罵人。更不用說,開車罵人,搶行,不排隊,板着面孔訓人,把“溫良恭儉讓”遠遠拋在了後面。今天我們不但要撿回溫良恭儉讓,更要加以發揮,我認爲,最重要的發揮是把這箇中國的優秀傳統推廣到國際關係方面。

溫良恭儉讓這五個字是金玉之言。但是我們看看國際關係中從來也不用這五個字。有哪位外交官在外交場合上向對方說“對不起”?更不會在正式文件中寫上“請原諒”?相反,倒是經常用馬路上兩個人吵架的語言,生怕向對方屈膝,丟了面子。今天我們看看南北朝鮮互相說的話,極其典型地抄襲了馬路上吵架的話,不過更強硬,更難聽。中日兩國關於釣魚島的事所用的語言也好不到哪裏去。這樣對兩國的百姓有好處嗎?百姓們也不知不覺地覺得強硬纔有面子。從來也不想一想外交場合是不是也應該講“溫良恭儉讓”?到底怎樣對兩國人民更有利?人類文明積累的精華難道只適用於個人關係,不能用於國際關係嗎?

戰爭與和平的大事至今仍然是全世界百姓最爲關心的事。兩次世界大戰的教訓太深刻了。用這麼大的代價獲得的教訓值得我們深深記住。消滅戰爭要多管齊下。國家要走上民主政治之路。像朝鮮這樣的國家最容易發動戰爭。二戰後的幾次戰爭多半發生在獨裁國家之間,或與獨裁政治有關。兩個民主國家不可能會打仗。裁軍也是一條重要的避免戰爭的方法。再就是外交場合下的禮儀,防止越走越偏,擦槍走火。戰爭最終的受害者是老百姓。可是老百姓又是被欺騙上戰場的主體。他們往往上當受騙。百姓的覺醒是消滅戰爭的最根本的道路。希望我們的百姓能監督自己的外交官遵循“溫良恭儉讓”的原則處理外交事務,不讓他們拿戰爭與和平開玩笑,像馬路上吵架的人那樣。


^ permalink raw reply	[flat|nested] 3+ messages in thread

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-- links below jump to the message on this page --
2013-04-15  8:34 "No definition" for "per-file basis in a source code block" mode Wolfkin Chiang
2013-04-15 11:38 ` Suvayu Ali
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2013-04-08  5:18 Wolfkin Chiang

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