Dependency Injection docs

[peterneyens]

Did I miss something, or do we need something else?

I tried to come up with a simple but not too trivial example of using Reader / Kleisli as target data type where you do not want the environment or config to be part of your algebra (like with ReaderM), but I couldn't come up with something small but still useful.

I don't know if it makes sense to add something trivial like :

@free trait Calc[F[_]] {
  def sum(a: Int, b: Int): FreeS[F, Int]
}

type IntReader[A] = Reader[Int, A]

implicit val handler: Calc.Handler[IntReader] = new Calc.Handler[IntReader] {
  def sum(a: Int, b: Int): IntReader[Int] = Reader(n => a + (b * n))
}

Calc[Calc.Op].sum(1, 2).exec[IntReader].run(5) // 11 (= 1 + 2 x 5)

Resolves #132.

[codecov-io]

Codecov Report

Merging #195 into master will not change coverage.
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  Hits          231      231           
  Misses         92       92

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[raulraja]

I think we need to mention here that we include synthetic implicits in all Algebras and Modules so you can inject them anywhere by requiring them implicitly, that should be the main part of the docs. then provide examples of that. The actual Reader example should be mentioned as an alternative secondary technique just to show that freestyle supports other styles of DI via the reader effect where you can inject other things beside config