yamlate

A cross-language interpreter library that dynamically evaluates YAML attributes given variable bindings

What it does:

Given a mapping of variables to values, it evaluates YAML properties written in a special language dynamically. It also can update the variables in the mapping so it can change its "state".

Language features inside YAML are prefixed with '~>' so the interpreter can know to evaluate them.

Hypothetical use case:

Lets say that you want to gather data from around a couple thousand bug species. Each bug has different behavior. Some change their wing color based on the season, and others change their wing color when another bug is nearby. Once a bug changes their wing color when another bug is nearby, the other bug leaves and there is no longer another bug nearby.

One way to model this is to hardcode the bug behavior using something similar to a strategy pattern. You could create a thousand different code files for all of the bugs.

One problem with this is that writing code for every bug ties the data to the code which makes it hard for non-developers to understand the core logic and ties the data to a specific language (Java, Python, etc).

Another way is to use a markup language like XML or a data serialization format like YAML so that the data is abstracted from the code.

One problem with this is that there is a lot of complex logic and data is being transformed (the other bug leaving changes the environment) so something like YAML won't be enough.

With Yamlate, you can do something like this:

cricket:
  wing_span: 3.5
  wing_color:
    - if:
      - '~> current_season == "spring"'
      - do:
        - 'red'
        else:
        - 'blue'
        
beetle:
  wing_span: 2.9
  wing_color:
    - if:
      - '~> another_beetle_nearby == 1'
      - do:
        - '~> another_beetle_nearby = 0'
        - 'blue'
        else:
        - 'red'

# etc... for all of the bugs

This allows you to have the advantages of YAML with the ability to model more complex logic.

You can also write a program in your favorite language (right now only python :P) to retrieve the data:

lib = ctypes.cdll.LoadLibrary("../target/release/libyamlate.dylib")
yamlate = Yamlate(lib)

with yamlate.new_environment() as environment:
    environment.set_integer('another_beetle_nearby', 1)
    environment.set_string('current_season', 'spring')
        
    with open('../examples/bug.yaml', 'r') as yaml_file:
        data = yaml_file.read()
            
        with yamlate.new_yaml_from_str(data) as root_yaml:
            with root_yaml.hash_get('cricket') as cricket_yaml:
                with cricket_yaml.hash_get('wing_color') as wing_yaml:
                    with wing_yaml.evaluate(environment) as cricket_wing_result:
                        # should print 'red'
                        print cricket_wing_result.get_string()
                                        
            with root_yaml.hash_get('beetle') as beetle_yaml:
                with beetle_yaml.hash_get('wing_color') as wing_yaml:
                    with wing_yaml.evaluate(environment) as beetle_wing_result:
                        # should print 'blue'
                        print beetle_wing_result.get_string()
                        
                        # should print '0'
                        print environment.get_integer('another_beetle_nearby')

Note: the python wrapper is pretty verbose, hopefully I can refactor it into something better

For the full example look at the python/python_example_bug.py for the python file and the examples/bug.yaml for the YAML file

Why Rust?

Exposes a C interface so that all languages with C FFI support (essentially all modern languages) can call into the library
Performance characteristics similar to C and C++
Safe by default (prevents not only memory problems but a whole host of other problems as well)
Easy testing out of the box (no confusing linking or setup problems like in C/C++)

Building

You have to use cargo to build the project into a dynamic library.

cargo build --release

The resulting library is at ./target/release/libyamlate.dylib

Contributing

Contributions are welcome! Make sure that all of the existing test cases pass (from cargo test) and if you are adding features you are adding additional test cases.

Make sure that you are not getting any warnings from clippy.

If you are getting clippy warnings there will be a line after the warning with something like this:

help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#<clippy_warning_here>