Romanesco

Romanesco allows you to parse simple mathematical expressions, and creates a fully object-oriented expression tree for evaluation.

You can inject variable values at runtime so that formulae can be used, edited and re-saved as part of an application.

Currently Romanesco supports the four basic operators (addition, subtraction, multiplication, division) as well as parentheses. It supports the use of constants and named variables.

Written by Charlie Ablett of Arctic Fox Computer Consulting (NZ) with support from Dr Craig Taube-Schock.

MIT License.

So named because Romanesco broccoli has self-repeating patterns, much like the structure of the resulting expression tree. Also, it's delicious.

Installation

Add this line to your application's Gemfile:

gem 'romanesco'

And then execute:

$ bundle

Or install it yourself as:

$ gem install romanesco

Usage

You can use Romanesco as a basic calculator if you want.

expression = Romanesco.parse("1+10*3")
result = expression.evaluate #=> 31.0
original_expression = expression.to_s #=> "1 + 10 * 3"

If you have variables, inject them as follows:

expression = Romanesco.parse("a * (b + c)")
result = expression.evaluate(a: 5, b: 2, c: 10) # => 100.0
original_expression_string = expression.to_s # => "a * (b + c)"

In fact, you can inject anything that responds to the message evaluate(options)...

class OneHundred
  def evaluate(options)
    100
  end
end

expression = Romanesco.parse("one_hundred + 2.2")
result = expression.evaluate(one_hundred: OneHundred.new) # => 102.2        

... including other expressions (Don't worry, in this case we can detect infinite loops):

dangerous_animals = Romanesco.parse("honey_badgers + dangerous_australian_animals")
australian = Romanesco.parse("box_jellyfish + snakes")
result = dangerous_animals.evaluate(box_jellyfish: 10, snakes: 4, dangerous_australian_animals: australian, honey_badgers: 1) #=> 15    

Get a list of the variables you'll need by calling required_variables:

expression = Romanesco.parse("(lions + tigers) * bears")
required = expression.required_variables #=> [:lions, :tigers, :bears]

If you're missing any variables, Romanesco will let you know:

expression = Romanesco.parse("maine_coon * japanese_bobtail")
 
begin
  expression.evaluate
rescue Romanesco::MissingVariables => e
  e.missing_variables #=> [:maine_coon, :japanese_bobtail]
end

Otherwise, you can provide a default value for any missing variables:

expression = Romanesco.parse("maine_coon * japanese_bobtail")

expression.evaluate({}, 3) #=> 9.0

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request