Eqn

Eqn uses the Treetop parser generator to safely evaluate mathematical expressions in Ruby.

Installation

Add this line to your application's Gemfile:

gem 'eqn'

And then execute:

$ bundle

Or install it yourself as:

$ gem install eqn

Usage

To evaluate an equation string, run the following:

$ Eqn::Calculator.calc('1 + 1')
# => 2

You can also check if an equation is valid:

$ Eqn::Calculator.valid?('1 + 1')
# => true
$ Eqn::Calculator.valid?('1 + / 1')
# => false

If you want to peek at how Eqn is parsing an equation, run the following to get the syntax tree:

$ Eqn::Parser.parse('1 + 1')
# => <syntax tree is printed>

Eqn follows the standard mathematical order of operations: parentheses, exponentiation, multiplication/division, addition/subtraction. It ignores whitespace, so 1 + 1 === 1+1. (However, it does not ignore whitespace between two numbers, so 1 1 is invalid.)

Variables

Eqn supports dynamically inserting values into an equation. Variables are passed to the calculator method via a hash; variable names may contain any lowercase or uppercase letters. Some examples:

$ Eqn::Calculator.calc('a + 1', a: 1)
# => 2

$ Eqn::Calculator.calc('5 * value', value: 2.5)
# => 12.5

$ Eqn::Calculator.calc('if(a > 10, b, c)', a: 15, b: 1, c: 0) # see below for function documentation
# => 1

Functions

Eqn presently supports four functions:

if

Syntax: if(comparison, value_if_true, value_if_false)

For example, if(5 > 3, 1, 2) would evaluate to 1.

round

Syntax: round(number)

Rounds the number up if the decimal is greater than 0.5 and down otherwise (i.e. "normal" rounding).

roundup

Syntax: roundup(number)

Rounds the number up to the next whole integer (i.e. ceiling function)

rounddown

Syntax: rounddown(number)

Rounds the number down to the next whole integer (i.e. floor function)

Development

After checking out the repo, run bin/setup to install dependencies. Then, run bin/console for an interactive prompt that will allow you to experiment.

The gem uses rspec for testing; run rspec from the application root to execute the tests.

Authorship

Written by Zach Schneider for Aha!, the world's #1 product roadmap software

Contributing

1. Fork it ( https://github.com/schneidmaster/eqn/fork )
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 a new Pull Request