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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](CONTRIBUTING.md)---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](https://kiwiirc.com/nextclient/irc.libera.chat/?nick=Guest?#disco-lang).

Documentation
-------------

Documentation is [hosted on
readthedocs.io](http://disco-lang.readthedocs.io/en/latest/).

Contributing
------------

If you'd like to contribute to disco development, check out
[CONTRIBUTING.md](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](http://ozark.hendrix.edu/~yorgey/install-haskell.html).

- 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](https://brew.sh/) (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](https://github.com/disco-lang/disco/issues/253).

    - 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](https://github.com/disco-lang/disco/issues/new).  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!