Systems

systems is a set of tools for describing, running and visualizing systems diagrams.

Installation directions are below, and then get started by working through the tutorial or reading through the Jupyter notebook example example.

For a more in-depth look at the system syntax, please read the syntax specification.

Quickest start

Follow the installation instructions below, then write a system definition such as:

Start(10)
Start  > Middle @ 2
Middle > End

You can then evaluate your system (use --csv for an importable format):

cat tmp.txt | systems-run -r 3

        Start   Middle  End
0       10      0       0
1       8       2       0
2       6       3       1
3       4       4       2

See the tutorial for more detailed starting information.

Jupyter notebooks

Likely the easiest way to iterate on a model is within a Jupyter notebook. See an example notebook here. Read this blog post for more installation details.

Installation

To install via PyPi:

pip install systems

To install for local development:

git clone https://github.com/lethain/systems.git
cd systems
python3 -m venv ./env
source ./env/bin/activate
python setup.py develop

Run tests via:

python3 -m unittest tests/test_*.py

Or run a single test via:

python3 tests/test_parse.py TestParse.test_parse_complex_formula

Please open an Github issue if you run into any problems!

Using the command line tools

There are four command line tools that you'll use when creating and debugging systems/

systems-run is used to run models:

$ cat examples/hiring.txt | systems-run -r 3
PhoneScreens    Onsites Offers  Hires   Employees       Departures
0       0               0       0       0       5               0
1       25              0       0       0       5               0
2       25              12      0       0       5               0
3       25              12      6       0       5               0

systems-viz is used to visualize models into Graphviz:

$ cat examples/hiring.txt | systems-viz
// Parsed
digraph {
  rankdir=LR
  0 [label=Candidates]
  1 [label=PhoneScreens]
  // etc, etc, some other stuff
}

Typically you'll pipe the output of systems-viz into dot, for example

$ cat examples/hiring.txt | systems-viz | dot -Tpng -o tmp.png

systems-format reads in a model, tokenizes it and formats the tokens into properly formatted results. This is similar to gofmt, and could be used for ensuring a consistent house formatting style for your diagrams. (It was primarily implemented to support generating human readable error messages instead of surfacing the tokens to humans when errors arise.)

$ cat examples/hiring.txt | systems-fmt
[Candidates] > PhoneScreens @ 25
PhoneScreens > Onsites @ 0.5
# etc etc

systems-lex generates the tokens for a given system file. This is typically most useful when you're extending the lexer to support new types of functionality, but can also be useful for other kinds of debugging:

$ cat examples/hiring.txt | systems-lex
('lines',
   [('line',
     1,
     [('comment', '# wrap with [] to indicate an infinite stock that')]),
    ('line', 2, [('comment', "# isn't included in each table")]),
('line', 3, [('comment', '# integers are implicitly steady rates')]),
('line',
 4,
     [('infinite_stock', 'Candidates', ('params', [])),
  ('flow_direction', '>'),
      ('stock', 'PhoneScreens', ('params', ())),
      ('flow_delimiter', '@'),
      ('flow', '', ('params', (('formula', [('whole', '25')]),)))]),
...
  ]
)

Error messages

The parser will do its best to give you a useful error message. For example, if you're missing delimiters:

cat examples/no_delim.txt | systems-run
line 1 is missing delimiter '>': "[a] < b @ 25"

At worst, it will give you the line number and line that is creating an issue:

cat examples/invalid_flow.txt | systems-run
line 1 could not be parsed: "a > b @ 0..2"

Uploading distribution

If you are trying to install this on PyPi, the steps are roughly:

python3 -m pip install --user --upgrade pip
python3 -m pip install --user --upgrade wheel
python3 -m pip install --user --upgrade twine
python3 setup.py sdist bdist_wheel
twine upload --repository-url https://upload.pypi.org/legacy/ dist/*

That should more or less work. :)