Scala Traversable

Going a bit further in Functional Programming concepts with Traversable

We already saw a few concepts so far such as Functor and Applicative.
Let’s dig deeper !

Traversable solves a specific problem. How to apply an operation to many inputs at once without leaving the “Box/Container/F” ?

Without Traversable, we would have to perform something like this:

val input: List[Int] = List(1,2,3)
val operation: Int => F[Int] = ???

val output: List[F[Int]] = input.map( i => operation(i))

But how do we manage to get F[List[A]] instead of List[F[A]] ? Traversable !

To implement traverse we re-use what we built in the previous episodes: Functor and Applicative. So we can chain the operation and wrap into F.

With traverse which allows you to apply an operation to many element and stay inside F, we also get for free sequence which allow you to flip List[F[A]] inside out into F[List[A]]. You will see it in Future.sequence for instance that is very convenient to wait or combine many Future together.

As a note: input.map(f).sequence is the same as input.traverse(f).

Reveal more information and clues
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