http://github.com/rubysolo/dentaku
Dentaku is a parser and evaluator for a mathematical and logical formula language that allows run-time binding of values to variables referenced in the formulas.
This is probably simplest to illustrate in code:
calculator = Dentaku::Calculator.new
calculator.evaluate('10 * 2')
=> 20
Okay, not terribly exciting. But what if you want to have a reference to a variable, and evaluate it at run-time? Here's how that would look:
calculator.evaluate('kiwi + 5', :kiwi => 2)
=> 7
You can also store the variable values in the calculator's memory and then evaluate expressions against those stored values:
calculator.store(:peaches => 15)
calculator.evaluate('peaches - 5')
=> 10
calculator.evaluate('peaches >= 15')
=> true
For maximum CS geekery, bind is an alias of store.
Dentaku understands precedence order and using parentheses to group expressions to ensure proper evaluation:
calculator.evaluate('5 + 3 * 2')
=> 11
calculator.evaluate('(5 + 3) * 2')
=> 16
A number of functions are also supported. Okay, the number is currently two,
but more will be added soon. The current functions are round and if, and
they work like their counterparts in Excel:
calculator.evaluate('if (pears < 10, 10, 20)', :pears => 5)
=> 10
calculator.evaluate('if (pears < 10, 10, 20)', :pears => 15)
=> 20
Round can be called with or without the number of decimal places:
calculator.evaluate('round(8.2)')
=> 8
calculator.evaluate('round(8.2759, 2)')
=> 8.28
If you're too lazy to be building calculator objects, there's a shortcut just for you:
Dentaku('plums * 1.5', {:plums => 2})
=> 3.0
Math: + - * /
Logic: < > <= >= <> != = AND OR
Functions: IF ROUND
Big thanks to ElkStone Basements for allowing me to extract and open source this code.
(The MIT License)
Copyright © 2012 Solomon White
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.