Yodl stands for `Your Own Document Language' (originally: Yet Oneother
Document Language) and is basically a
pre-processor to convert document files in a special macro language (the Yodl
language) to any output format. The Yodl language is not a `final' language,
in the sense that it can be viewed or printed directly. Rather, a document in
the Yodl language is a `pre-document', that is converted with some macro
package to an output format, to be further processed.
Yodl was designed in 1996 by Karel Kubat when he needed a good document
preprocessor to convert output to either LaTeX (for printing) or to
HTML for publishing
via a WWW site. Although SGML does this too, he wanted something that is used
`intuitively' and with greater ease. This is reflected in the syntax of the
Yodl language, in the available macros of the Yodl macro package, and very
probably also in other aspects of Yodl. However, Yodl is designed to convert
to any output format; so it is possible to write a macro package that
converts Yodl documents to, say, the man format for manual pages.
Some highlights of Yodl:
Yodl allows the inclusion of files. This makes it easier to split up
a document into `logical' parts, each kept in a separate file. Thus, a `main
document' file can include all the sub-parts. (Imagine that you're the editor
of a journal. Authors are likely to send in their submissions in separate
files; inclusion can then be very handy!)
Yodl is
described.)
Yodl supplies an extension if none is present. The default
extension is .yo, but can be defined to anything in the compilation of the
Yodl program.
Yodl supports conditional parsing of its input, controlled by defined
symbols. This resembles the #ifdef / #else / #endif preprocessor
macros of the C language. Yodl also supports other if clauses, e.g.,
to test for the presence of an argument to a macro.
Yodl offers hooks to define counters, to modify them, and to use them
in a document. Thereby Yodl offers the possibility for automatic numbering of
e.g., sections. Of course, some document languages (e.g., LaTeX) offer this
too; but some don't. When converting a Yodl document to, say, HTML, this
feature is very handy.
Yodl is designed to be easy to use: Yodl uses `normal' characters to
identify commands in the text, instead of insisting weird-looking tags or
escape characters. Editing a document in the Yodl macro language is designed
to be as easy as possible.
Yodl supports `character
conversion tables' which define how a character should appear in the output.
Yodl from the point of the user: how can
macros be defined, how is the program used etc.. Next, my own macro package is
presented and the macros therein described. Finally, this document holds
technical information about the installation and the inner workings of Yodl.
Yodl Version 4.00.00 some old features were removed, and several new ones
were introducted.
Yodl
2.00.00, were removed:
SUBST definitions;
SUBST definitions
that was active just before the last PUSHSUBST call;
verb macro now starts with PUSHSUBST(0) and ends with
POPSUBST().
Yodl
2.00.00, were removed:
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First of all, Yodl may lower the threshold of new users to start writing
documents. An example of an excellent, though not very user-friendly document
language is LaTeX. Typing all the backslash and curly brace characters in
LaTeX and remembering that an asterisk must be typed as $*$ may be hard
at first. In such situations, a properly configured Yodl macro set removes
these obstacles and thereby helps novices. Yodl is designed to be easy to
learn. As the Yodl package is growing, so is the manual. The ease of
`learning Yodl' may thus somewhat diminish, but just keep in mind: as long as
you need just plain texts, Yodl does OK. If you want more functionality, e.g.,
the composition of manual pages for Unix, dig into the documentation.
Second, Yodl permits to create more than one macro set, defining the same commands, but leading to different output actions. Thereby, the same input file can be converted to several output formats, depending on the loaded macro set. In this, Yodl is a `general front' document language, which converts a Yodl document to a specialized language for further processing. This was of course one of my reasons to write Yodl: I needed a good converter for either LaTeX or HTML.
Third, Yodl always allows an `escape route' to the output format. Most situations can be handled with Yodl macros, but sure enough, some users will want special actions for a given output format. A typical example for the necessity of such an escape route is the typesetting of mathematical formulas. Say you want to use Yodl for a document that is converted either to LaTeX (being a very good mathematical typesetter) or to HTML (a very poor mathematical typesetter). An approach might be to decide inside the document how to typeset a mathematical formula. Yodl provides conditional command processing to accomplish this. The decision would be based on the output format: for LaTeX, you'd typeset the formula using all the facilities that LaTeX offers, and for HTML you'd use poor-mans typesetting. Typically, other pre-processors for documents don't allow such escape routes. Well, Yodl does.