Dentaku
=======

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http://github.com/rubysolo/dentaku

DESCRIPTION
-----------

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.

EXAMPLE
-------

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 five,
but more will be added soon.  The current functions are
`if`, `not`, `round`, `rounddown`, and `roundup`, 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`, `rounddown`, and `roundup` 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

`round` and `rounddown` round down, while `roundup` rounds up.

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


BUILT-IN OPERATORS AND FUNCTIONS
---------------------------------

Math: `+ - * / %`
Logic: `< > <= >= <> != = AND OR`
Functions: `IF NOT ROUND ROUNDDOWN ROUNDUP`


EXTERNAL FUNCTIONS
------------------

See `spec/external_function_spec.rb` for examples of how to add your own functions.

The short, dense version:

Each rule for an external function consists of three parts: the function's name,
a list of tokens describing its signature (parameters), and a lambda representing the
function's body.

The function name should be passed as a symbol (for example, `:func`).

The token list should consist of `:numeric` or `:string` if a single value of the named
type should be passed; `:non_group` or `:non_group_star` for grouped expressions.

> (what's the difference? when would you use one instead of the other?)

The function body should accept a list of parameters. Each function body will be passed
a sequence of tokens, in order:

1. The function's name
2. A token representing the opening parenthesis
3. Tokens representing the parameter values, separated by tokens representing the commas between parameters
4. A token representing the closing parenthesis

It should return a token (either `:numeric` or `:string`) representing the return value.

Rules can be set individually using Calculator#add_rule, or en masse using Calculator#add_rules.


THANKS
------

Big thanks to [ElkStone Basements](http://www.elkstonebasements.com/) for
allowing me to extract and open source this code.

LICENSE
-------

(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.