omkarmoghe / Open-ELO

Open ELO

Models

Scalar

A Scalar is the simplest object that can be evaluated. It holds a single value. When used in an Expression, this value must respond to the symbol (i.e. support the method) defined by the Expression#operator.

Scalar.new(1)

Variable

A Variable represents a named value stored in the Environment. Unlike Scalars, Variables have no value until they are evaluated by an Environment. Evaluating a Variable that isn't present in the Environment will result in a MissingVariableError.

Variable.new("variable_a")

Expression

An expression represents 2 or more operands that are reduced using a defined operator. The operands of an Expression can be Scalars, Variables, or other Expressions.

And Expression can store its result back into the Environment by defining an output.

# addition
Expression.new(:+, Scalar.new(1), Scalar.new(2))

# multiplication
Expression.new(:*, Variable.new("variable_a"), Scalar.new(2))

# storing output
Expression.new(:+, Scalar.new(1), Scalar.new(2), output: "one_plus_two")

Environment

The Environment holds state in the form of a variables hash and can evaluate Expressions, Scalars, and Variables within a context. The environment handles updates to the state as Expressions run.

environment = Environment.new(
  "variable_a" => 1,
  "variable_b" => 2,
)

environment.evaluate(Variable.new("variable_a"))
#=> 1

environment.evaluate(
  Expression.new(
    :+,
    Variable.new("variable_a"),
    Variable.new("variable_b"),
    output: "variable_c" # defines where to store the result value
  )
)
#=> 3

environment.variables
#=> { "variable_a" => 1, "variable_b" => 2, "variable_c" => 3 }

When evaluating multiple objects at a time, the value of the last object will be returned.

environment = Environment.new
environment.evaluate(
  Scalar.new(1),
  Expression.new(:+, Scalar.new(1), Scalar.new(2))
)
#=> 3

Serialization

All models support serialization via:

• as_json: builds a serializable hash representation of the object
• to_json: builds a JSON string representing the object

Building

1. Make sure you have Ruby installed, see .ruby-version for the version.
2. Install Bundler: gem install bundler
3. Use bundler to install dependencies: bundle install

Testing

Spec files are located in /test. Run all tests using bundle exec rake test.