Propellor is a single system, but it's made up of some logically separate
components.

* Propellor is a Haskell library. The library can be installed
  [from hackage](http://hackage.haskell.org/package/propellor)
  in the usual ways. It complies with the
  [[Haskell Package Version Policy|interface_stability]].
* `~/.propellor/` is a git repository, which contains at least your
  `config.hs` file and a cabal file. This gets deployed to each machine
  you manage with propellor, where it's installed as `/usr/local/propellor/`
* There can also be a propellor command in your PATH. If you `apt-get
  install propellor`, you'll get one installed, or `cabal install propellor`
  will put the command in `~/.cabal/bin/propellor`. This propellor command
  is just a wrapper; it builds and runs what you have set up in `~/.propellor/`

Typically, the `~/.propellor/` git repository is set up by running the
propellor command, or by [[cloning propellor|install]]. That makes
the repository contain the full source code to propellor, including
the Haskell library.

So if you want to, you can edit any part of Propellor's source code.
Don't like how a property works, or need to make it more general? Just edit
then copy in `~/.propellor/src/Propellor/` and it will be used. See
[[contributing]] if you want to send your improvements back.

All that really needs to be in `~/.propellor/` though, is a `config.hs`
file, and a cabal file. If you want to set up the repository manually,
and don't want it to contain propellor's source code, here's a stub cabal
file to get you started:

<pre>
Name: foo
Cabal-Version: >= 1.6
Build-Type: Simple
Version: 0

Executable propellor-config
  Main-Is: config.hs
  GHC-Options: -Wall -threaded -O0
  Build-Depends: propellor, base >= 3
</pre>

See [[haskell_newbie]] for an example config.hs file.