ly2mei

Andrew A. Cashner, andrewacashner@gmail.com

Description

Converts files written in a strict dialect of Lilypond to MEI-XML. This program is primarily a proof of concept.

The program is basically a compiler that reads a subset of the Lilypond language and produces MEI. (It does not use the Lilypond program at all.) The program can only work with a predictable, rule-bound portion of the Lilypond language and includes no support at all for Scheme.

Its main feature is that it can read files written in the one-voice-at-a-time, measure-wise format of Lilypond and transform the data to the one-measure-at-a-time format of MEI.

It also implements a basic macro expander that actually allows more flexibility than Lilypond itself. With the definition macro = "string" or macro = { expression in braces } starting on a new line, you can use \macro anywhere, even before the definition, without worrying about the mode or type of expression.

Aspirations and Conclusions

My goal was to evaluate the feasibility of this approach while experimenting with programming techniques that were relatively new to me: object-oriented programming in a lower-level language than I had been using (having just come from a large project in Haskell). I wanted to write clear, well-documented code and after working in a pure-functional language I wanted to use something close to a functional style while getting practice managing memory.

I hoped to be able to convert my own Lilypond projects (editions of 17th-century Spanish villancicos) to MEI. I had written them in a LaTeX-like interface for Lilypond I had developed (my lirio "package"), which aimed to eliminate mixing semantic or content-oriented code with low-level overrides and other Lilypond ugliness. Nevertheless, some complexity was just unavoidable when I had to make both parts and scores (using \keepWithTags for example), add figured bass, and many other features. In the end (so far anyway) this goal remains out of reach but I learned a lot about programming and music encoding.

If you find some part of this project useful or would like to pick it up where I've left off, please reach out.

Limitations

The program is not really intended for general use although it can do a lot.

• No abbreviations or shortcuts. There must be an explicit octave mark and rhythmic value after every single pitch.
• Every bar must be marked with |.
• No Scheme functions.
• Lilypond commands not hard-coded into this program will be ignored.
• Including files works if they just contain simple key = value macro definitions but not if they contain elaborate Lilypond configuration, Scheme code, etc.
• No <<...>> expressions within a music expression.
• No figured bass or chord mode.

Bonus features

The macro expander module in this program actually allows you to define simple macros that Lilypond doesn't allow. Lilypond macros are typed (music mode, lyric mode, etc.), where these macros are simple text substitutions. There is no problem with writing Text = { a -- ny -- thing } and then later writing \lyricmode \Text, where with Lilypond you would have to use \lyricmode to create the macro to begin with.

The program supports many of the commands I created for my own lirio Lilypond "package", which I used for typesetting editions of 17th-century Spanish choral music. So in addition to \time 3/2 you can write \MeterTriple and instead of key f\major you can write \CantusMollis. Coloration brackets work with \color and \endcolor, e.g, a'2\color b'2\endcolor. Section headings, instrument names, and incipit staves are not (yet) supported, unfortunately. (Not for lack of trying...)

Implementation

Written in Object Pascal for the Free Pascal Compiler. Documentation generated by PasDoc.

Requirements

• GNU Make
• fpc
• PasDoc
• For PDF documentation: TeXLive and my code2pdf script (see below)

Build

• Executable: make
• HTML documentation of unit interfaces: make doc and make view to read the docs in the browser
• PDF documentation, including source code: make pdfdoc and make view-pdf
• Clean up: make clean

Testing and Debugging

• Build in test mode (show all compiler messages and report on memory usage): make TEST=1
• Build in debug mode (show all verbose debug messages): make DEBUG=1

Read documentation

• View HTML documentation: make view
• View PDF documentation: make view-pdf

License

Copyright © 2022 Andrew A. Cashner.

This work is made available under the MIT license, see the LICENSE file.

I would love to hear from you if you are using the program or its code (see e-mail above).