Boolean DSL

Boolean DSL is a simple boolean language for creating business rules

Installation

Add this line to your application's Gemfile:

gem 'boolean_dsl'

And then execute:

$ bundle

Or install it yourself as:

$ gem install boolean_dsl

Usage

A context is simply a Ruby object. A script is a string of our DSL consisting of an expression (described below). The result of the expression will be true or false, and that is what BooleanDsl::Evaluator#outcome will return.

require 'boolean_dsl'

context = Context.new
script = "(1 < 4 or 5 < 4) and (1 == 1 and alpha == 1)"
BooleanDsl::Evaluator.new(script, context).outcome

Attribute references (as described below), are simply the names of method on the context. i.e. in the example above, it will call the alpha method of the context.

DSL

Our DSL consists of these components:

• string, a sequence of characters, delimited by '' (single quotes), may contain any character other than a single quote. Examples:

  'alpha'
  'What is your name?'
  

• integer, a sequence of [+-]?[0-9]*. Examples:

  0
  -654
  458457474
  

• decimal, a sequence of [+-]?[0-9]*.[0-9]*. Examples:

  0.123
  -45.78
  

• percentage, a sequence of [+-]?[0-9]*(.[0-9])?%*. Examples:

  43.56%
  -20%
  

• array, a comma separated list of integer, decimal or string elements wrapped by [] (square brackets)

  [1,2,3]
  

• attribute reference, a sequence of [A-z_][A-z0-9_]*[?]. When an attribute reference is evaluated, the context.send(attribute_reference) is called, and the result is used as the attribute's value. An attribute may optionally be prefixed by a ! (exclamation point). The result is the logial NOT of the attribute's value. Examples:

  beta
  Apple_Tree
  what_i5_YOUR_name?
  !beta
  !Apple_Tree
  !what_i5_YOUR_name?
  

• element is one of a string, percentage, decimal, integer, array or attribute.

• comparison consists of an element, followed by one of ==, !=, <, >, <=, >=, includes, excludes (the operator) followed by another element. When a comparison is evaluated, the 2 elements are compared using the operater supplied. The comparison follows Ruby evaluation rules. The result is used as the result of the comparison. Examples:

  1 < 2
  'test' == beta
  alpha != delta
  8 >= 1
  [1,2,3] includes 3
  

• boolean expression consists of a left side, followed by one of and, or (the operator), followed by a right side.

  The left side consists of a attribute or a comparison. The right side consists of an expression.

  When the boolean expression is evaluated, the results of the 2 sides are evaluated against the operator. The evaluation follows Ruby rules, including short-circuiting.

  The boolean expression may optionally be wrapped in () (parentheses), which forces the content of the parentheses to be evaluated independently of the rest of the script (i.e. it forces operator precedence). Examples:

  1 < 2 and 3 < 4
  beta or gamma != 'test'
  2 < 10 or (potato and 1 != 10)
  (6 > 7)
  

• expression is one of a boolean, comparison, or element. When the expression is evaluated, the result is the result of the boolean, comparison, or element.

  The expression may optionally be wrapped in () (parentheses), , which forces the content of the parentheses to be evaluated independently of the rest of the script (i.e. it forces operator precedence). Examples:

  8 >= 5
  beta == '1' or delta == '3'
  1 < 2 and 'alpha' == 'alpha' and 7 < 12
  8 == 8 or (beta != gamma and (delta > yotta))
  

Each component listed above may be surrounded by a single space; in the examples above, we have done this.

Contributing

1. Fork it ( http://github.com/jobready/boolean_dsl/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 new Pull Request