# Parallel Letter Frequency

Count the frequency of letters in texts using parallel computation.

Parallelism is about doing things in parallel that can also be done
sequentially. A common example is counting the frequency of letters.
Create a function that returns the total frequency of each letter in a
list of texts and that employs parallelism.

## Hints
According to [this terminology](http://chimera.labs.oreilly.com/books/1230000000929/ch01.html#sec_terminology) you should write a *parallel* and *deterministic*
program and (by all means!) let Scala deal with the *concurrency* aspect.
Or else your code could quickly get messy and error-prone with all kinds of nasty
concurrency bugs. In particular your program could become indeterministic
which spells in practice: very (in fact, VERY) hard to debug, test and reason about.

Having said that it might be a good idea to first write a sequential solution (and
use the test suite to verify it).
Only then should you try to parallelize it while keeping the sequential and parallel
portions of your code as separate as possible.

A first iteration could be using Scala's [parallel collections](http://docs.scala-lang.org/overviews/parallel-collections/overview.html). You might find
that this is almost too simple (especially if you have followed our advice and
already have a sequential solution).

For the second iteration we recommend you try a solution with [scala.concurrent.Future](http://www.scala-lang.org/api/current/scala/concurrent/Future$.html).
You can consult [this tutorial](http://danielwestheide.com/blog/2013/01/09/the-neophytes-guide-to-scala-part-8-welcome-to-the-future.html) and [its sequel](http://danielwestheide.com/blog/2013/01/16/the-neophytes-guide-to-scala-part-9-promises-and-futures-in-practice.html) for some help.
Make sure that you
- have only one single blocking call to wait for the result
- that it is at the very end of your program, and
- that it has a timeout.

`scala.concurrent.Future` is used in many libraries and the doctor's advice for
parallel and asynchronous programming in Scala. So it is essential for mastering
the language and it should become part of your Scala armory.


The Scala exercises assume an SBT project scheme. The exercise solution source
should be placed within the exercise directory/src/main/scala. The exercise
unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command `sbt test` in the exercise directory.

For more detailed info about the Scala track see the [help
page](http://exercism.io/languages/scala).



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