disco: Functional programming language for teaching discrete math.

Disco is a programming language intended to teach basic functional programming principles in the context of a discrete mathematics course.

Design principles

• Includes those features, and only those features, useful in the context of a discrete math course. This is not intended to be a general-purpose language.
• Syntax is as close to standard mathematical practice as possible, to make it easier for mathematicians to pick up, and to reduce as much as possible the incongruity between the language and the mathematics being explored and modeled.
• Tooling, error messages, etc. are very important---the language needs to be accessible to undergrads with no prior programming experience. (However, this principle is, as of yet, only that---there is no tooling or nice error messages to speak of.)

Feel free to look around, ask questions, etc. You can also contribute---collaborators are most welcome.

Community

Check out the disco IRC channel, #disco-lang on Libera.Chat. If you're not familiar with IRC, you can connect via this web client.

Documentation

Documentation is hosted on readthedocs.io.

Contributing

If you'd like to contribute to disco development, check out CONTRIBUTING.md.

Building disco

• The first step is to install the Haskell programming language (the language in which Disco is implemented). If you don't already have Haskell installed, you can follow the directions here.

• Now, at a command prompt, run cabal update, which will download the latest information about Haskell packages.

• Now run cabal install disco at a command prompt.

  • Note that this may take a very long time, on the order of an hour or so.

  • The good news is that most of this work only needs to be done once, even if you later install an updated version of disco. Even if installation fails partway through, the work already completed up to that point need not be redone.

  • On OSX, if building fails with an error like ghc: could not execute: opt, it means you need to install LLVM. The easiest way to do this is to first follow the instructions to install Homebrew (if you don't already have it), and then type

    brew install llvm
    

    at a terminal prompt.

    • If this fails with an error like Could not resolve HEAD to a revision, then try running these two commands at a terminal prompt:

      rm -rf $(brew --repo homebrew/core)
      brew tap homebrew/core
      

      Then re-run the brew install llvm command.

    • After installing llvm, you may need to close and re-open the terminal before running cabal install disco again.

• If it works, you should be able to now type disco at a command prompt, which should display a message like this:

  Welcome to Disco!
  A language for programming discrete mathematics.
  Disco>
  

• If installation seems like it succeeded but the disco command is not recognized, it may be an issue with your path environment variable settings. Try running disco using an explicit path:

  • ~/.cabal/bin/disco on Linux, OSX, or WSL2
  • C:\cabal\bin\disco on Windows
  • If those don't work, poke around and see if you can figure out where the cabal/bin folder is on your computer, and run disco from there.
  • If you wish, you may add the cabal/bin folder (wherever it is located) to your Path (Windows) or PATH (Linux/OSX) environment variable, so that you can run disco simply by typing disco. However, this step is optional.

• On Windows, if disco crashes with an error about foldr after you try to type anything (or if it simply closes the entire window when you type anything), the problem is probably that you need to enable UTF-8 mode.

  • Open a command prompt, and type

    chcp 65001
    

  • Now start disco as before (by typing disco or C:\cabal\bin\disco or whatever worked).

  • You will have to do this every time you run disco. Alternatively, you can create a file called disco.cmd containing those two commands, for example:

    chcp 65001
    C:\cabal\bin\disco
    

    Now you can simply double-click on disco.cmd to run disco.

If you encounter any difficulties, please let me know --- either come talk to me or open a GitHub issue. These instructions will be kept up-to-date with whatever helpful tips or workarounds I learn. So even if you encounter a difficulty but figure out the solution youself, let me know --- that way I can include the problem and solution here so others can benefit!