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The Unison language

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Unison is a modern, statically-typed purely functional language with the ability to describe entire distributed systems using a single program. Here's an example of a distributed map-reduce implementation:

-- comments start with `--`
mapReduce loc fn ifEmpty reduce data = match split data with
  Empty          -> ifEmpty
  One a          -> fn a
  Two left right ->
    fl = forkAt loc '(mapReduce loc fn ifEmpty reduce !left)
    fr = forkAt loc '(mapReduce loc fn ifEmpty reduce !right)
    reduce (await fl) (await fr)

This function can be either simulated locally (possibly with faults injected for testing purposes), or run atop a distributed pool of compute. See this article for more in-depth coverage of how to build distributed computing libraries like this.

Other resources:

Building using Stack

If these instructions don't work for you or are incomplete, please file an issue.

The build uses Stack. If you don't already have it installed, follow the install instructions for your platform. (Hint: brew update && brew install stack)

If you have not set up the Haskell toolchain before and are trying to contribute to Unison on an M1 Mac, we have some tips specifically for you.

$ git clone
$ cd unison
$ stack --version # we'll want to know this version if you run into trouble
$ stack build --fast --test && stack exec unison

To run the Unison Local UI while building from source, you can use the / script. It will download the latest release of unison-local-ui and put it in the expected location for the unison executable created by stack build. When you start unison, you'll see a url where Unison Local UI is running.

See development.markdown for a list of build commands you'll likely use during development.

Language Server Protocol (LSP)

View Language Server setup instructions here.

Codebase Server

When ucm starts it starts a Codebase web server that is used by the Unison Local UI. It selects a random port and a unique token that must be used when starting the UI to correctly connect to the server.

The port, host and token can all be configured by providing environment variables when starting ucm: UCM_PORT, UCM_HOST, and UCM_TOKEN.


See the documentation for configuration here