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# 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.
## Running tests
Execute the tests with:
```bash
$ elixir bob_test.exs
```
(Replace `bob_test.exs` with the name of the test file.)
### Pending tests
In the test suites, all but the first test have been skipped.
Once you get a test passing, you can unskip the next one by
commenting out the relevant `@tag :pending` with a `#` symbol.
For example:
```elixir
# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
```
Or, you can enable all the tests by commenting out the
`ExUnit.configure` line in the test suite.
```elixir
# ExUnit.configure exclude: :pending, trace: true
```
For more detailed information about the Elixir track, please
see the [help page](http://exercism.io/languages/elixir).
## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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