Rollex
======

A dice roller expression evaluator implementing the Pratt Parser (AKA Top-Down Operator Precedence) written in Elixir!

You may have seen [Dicer](https://github.com/olhado/dicer)... That was my old library, which used a basic recursive
descent parser/evaluator. This implementation uses a version of a the Pratt Parser algorithm, also known as
Top-Down Operator Precedence. With protocols compiled/consolidated, it runs a touch faster than the RC one.

Any suggestions/merge requests for performance tweaks is greatly appreciated!

Installation
============

Pre-requisites
--------------

* Erlang 17 or greater
* Elixir 1.0.0 or greater
* git (to clone the repository)

Running in Elixir's interactive shell
-------------------------------------

`iex -S mix`

For better performance, compile/consolidate protocols:

`mix compile.protocols`

`iex -pa _build/dev/consolidated -S mix`

From here, execute rolls like this:

`iex(1)> Rollex.roll "1+2+3"`

Adding as a mix dependency
--------------------------

In your mix.exs file:

```elixir
  def application do
    [mod: {MyApp, []},
     applications: [:rollex]]
  end
```

and this:

```elixir
  defp deps do
    [{:rollex, "0.1.0"}]
  end
```

Details
=======

Rollex is an elixir application that lets you evaluate dice rolls with simple arithmetic operators. 

* The operators supported are `+, -, /, *`.
* Grouping is via parentheses
* Polyhedral dice are designated using the `<quantity>d<sides>` format (Ex. 20d8 or D100).
* You can ask Rollex to take the top or bottom X rolls via the `^<quantity>` (take top) and `v<quantity>` (take bottom) symbols (Ex. `10d100^5` [take top 5 results from 10 rolls of a 100-sided die])

Why?
====

Because it was a yet another fun, somewhat non-trivial way to work in Elixir.

Thanks
======

Thanks to [Lukasz Wrobel](http://lukaszwrobel.pl/) for his [short series on RD parsing](http://lukaszwrobel.pl/blog/math-parser-part-1-introduction), as well as [Eli Bendersy's post on TDOP](http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing)!