# Forth

Implement an evaluator for a very simple subset of Forth.

[Forth](https://en.wikipedia.org/wiki/Forth_%28programming_language%29)
is a stack-based programming language. Implement a very basic evaluator
for a small subset of Forth.

Your evaluator has to support the following words:

- `+`, `-`, `*`, `/` (integer arithmetic)
- `DUP`, `DROP`, `SWAP`, `OVER` (stack manipulation)

Your evaluator also has to support defining new words using the
customary syntax: `: word-name definition ;`.

To keep things simple the only data type you need to support is signed
integers of at least 16 bits size.

You should use the following rules for the syntax: a number is a
sequence of one or more (ASCII) digits, a word is a sequence of one or
more letters, digits, symbols or punctuation that is not a number.
(Forth probably uses slightly different rules, but this is close
enough.)

Words are case-insensitive.

## Rust Installation

Refer to the [exercism help page][help-page] for Rust installation and learning
resources.

## Writing the Code

Execute the tests with:

```bash
$ cargo test
```

All but the first test have been ignored. After you get the first test to
pass, open the tests source file wich is located in the `tests` directory
and remove the `#[ignore]` flag from the next test and get the tests to pass
again. Each separate test is a function with `#[test]` flag above it.
Continue, until you pass every test. 

If you wish to run all tests without editing the tests source file, use:

```bash
$ cargo test -- --ignored
```

To run a specific test, for example `some_test`, you can use:

```bash
$ cargo test some_test
```

If the specfic test is ignored use:

```bash
$ cargo test some_test -- --ignored
```

To learn more about Rust tests refer to the [online test documentation][rust-tests]

Make sure to read the [Modules](https://doc.rust-lang.org/book/second-edition/ch07-00-modules.html) chapter if you
haven't already, it will help you with organizing your files.

## Feedback, Issues, Pull Requests

The [exercism/rust](https://github.com/exercism/rust) repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!

If you want to know more about Exercism, take a look at the [contribution guide](https://github.com/exercism/docs/blob/master/contributing-to-language-tracks/README.md).

[help-page]: http://exercism.io/languages/rust
[modules]: https://doc.rust-lang.org/book/second-edition/ch07-00-modules.html
[cargo]: https://doc.rust-lang.org/book/second-edition/ch14-00-more-about-cargo.html
[rust-tests]: https://doc.rust-lang.org/book/second-edition/ch11-02-running-tests.html

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.