Js 37 try monad

[jdesiloniz]

This PR contains our first basic implementation of the Try monad, with the following features:

• It's based on the category theory Swiftz types, conforming to Pointed, Functor, Applicative and Monad.
• Encapsulates Swift's throwable functions, by using the new do/try blocks in Swift 2.0. Encapsulated operations are evaluated. An operation result is stored in an Success type containing its value, or in a Failure type containing the catched exception.
• It allows pattern matching to decompose it, and has utility methods like isSuccess, isFailure, getOrElse... to work with its values.
• It implements the more important HOF with the same syntax (mostly) as in Scala: map, flatMap, filter, recover, recoverWith.
• CONS: Because of the strict nature of the Swift data-type system, so far recover and recoverWith only allow to return instances of Try of the same generic type as the original instance on which the function is applied to.

This PR also includes a couple of modifications to PartialFunctions to allow some functionality to Try's recover and recoverWith functions.

Could you please review, @anamariamv? Also, it'd be nice to have your thoughts on this, @raulraja

Thanks!

[anamariamv]

@raulraja could you review please? I reviewed it and I think that it's Ok.

[raulraja]

Looks great! Another handy OP here would be the catamorphism via fold. Not sure if Swiftz already implements a Foldable instance but the convenience method would be handy. Something in pseudo code like...

myTry<T> fold (fail = (ex) -> T , succ = (result) -> T)

[raulraja]

In any case this LGTM and we should consider adding our own foldable ops like the ones in Scalaz if SwiftZ doesn't already do so.

[jdesiloniz]

@raulraja You're right. Swiftz includes Foldable. I'll take a look on how to conform Try to the fold methods, or to implement one of our own if Swiftz's ones don't make sense. I'm going to create a separate issue for this :). Thanks!