There are two examples of simple, yet useful, pre-processors. The first is
literate.ex. It implements literate programming in Euphoria. See literate.ex
and hello.lex for more information about literate programming. To run this
example, at the command prompt, simply type:

eui hello.lex

The second is an ASP type pre-processor for Euphoria. It will take a HTML file
with Euphoria code intermixed in <% ... %> style tags and convert it to a 
legitimate Euphoria function that can be included from any parent program. 

* etml.ex - the actual pre-processor
* etmltest.ex - a test program that outputs the results of an ETML file
* hello.etml - a "Hello, World!" style ETML example file

To run this example, at the command prompt type:

eui etmltest.ex

Now, how does Euphoria know how to process these files? Look in the 
eu.cfg file in this directory. You will notice that there are lines
that look similar to:

-p le,lex:literate.ex

This tells Euphoria that a pre-processor exists for the extensions le and
lex. When it comes across one of these files, it knows that it can translate
the source file into a legitimate Euphoria file by calling literate.ex.

literate.ex and etml.ex adhere to a simple standard for being able to interface
with Euphoria. They must take 2 parameters, in_filename out_filename. They
must read the input from in_filename and write the resulting file to 
out_filename. If an error occurs while processing the input file, the pre-processor
should return a non-zero error code. This will tell Euphoria that the 
pre-processing has failed and it should cease trying any more to run the program.

The last pre-processor here is datesub.ex which is described in the Euphoria
mini-guide about the pre-processor. Please see that for more information.