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The core machinery of Alda, implemented in Clojure.


  • alda.lisp: a Clojure DSL for building a musical score

  • alda.parser: reads Alda code, interprets it as music events, and builds a score using alda.lisp

For more details about how each component works, see the alda-core development guide.



Development on the Alda core library requires that you have the Boot build tool installed. This allows you to run the tests and use other development tasks.

boot dev task

For a convenient development experience, you can follow this workflow:

  1. Make some changes to the code in this repo.

  2. Run boot dev. This runs an Alda server in the foreground using the latest release version of alda/server-clj and your local copy of the code (with your changes) as the alda/core library.

    By default, the server will run on port 27714, but if you'd like, you can specify another port via the -p / --port option.

  3. Now you can test your changes via the alda CLI, e.g.:

$ alda -p 27714 play -c "piano: c"

You might find it most convenient to start an Alda REPL connected to your development Alda server:

$ alda -p 27714 repl

boot test task

To run the unit test suite, run boot test.

When developing, you can run boot watch test in a separate terminal and the tests will re-run every time you make a change to a file.

Adding tests

It is generally good to add new test cases when fixing bugs and adding features. Test-driven development is a good workflow when developing alda-core.

The automated test battery includes smoke tests where we parse and evaluate all of the example Alda scores in the examples/ directory. If you add an additional example score, be sure to add it to the list of score files in test/alda/examples_test.clj.


Alda uses timbre for logging. Every note event, attribute change, etc. is logged at the DEBUG level, which can be useful for debugging purposes.

The default logging level is WARN, so by default, you will not see these debug-level logs; you will only see warnings and errors.

To override this setting (e.g. for development and debugging), you can set the TIMBRE_LEVEL environment variable.

To see debug logs, for example, you can do this:

export TIMBRE_LEVEL=:debug

When running tests via boot test and troubleshooting a failing test, it may be helpful to use debug-level logging by running TIMBRE_LEVEL=:debug boot test.


Copyright © 2012-2018 Dave Yarwood et al

Distributed under the Eclipse Public License version 1.0.

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