Initial sketch of optics module

[travisbrown]

This is a partial port from Argonaut in response to #39 and this question. If we can get some docs and tests in place before Shapeless 2.3.0 is out, I'd be happy to publish this with 0.2.0, but I don't want to wait for it.

[codecov-io]

Current coverage is 75.10%

Merging #78 into master will increase coverage by +1.93% as of 7df3639

Powered by Codecov. Updated on successful CI builds.

[travisbrown]

Example usage:

import cats.data.Xor
import io.circe._, generic.auto._, jawn._, optics._
import monocle.macros.Lenses

@Lenses case class Foo(count: Int)
@Lenses case class Qux(foo: Foo, s: String)

val toQux = JsonPath.root.x.y.at(2).as[Qux]
val incrementCount = toQux.composeLens(Qux.foo).composeLens(Foo.count).modify(_ + 1)

val Xor.Right(json) = parse("""
  { "x" : { "y" : [0, 1, { "foo" : { "count" : 3  }, "s" : "abcde" }] } }
""")

And then:

scala> json
res0: io.circe.Json =
{
  "x" : {
    "y" : [
      0,
      1,
      {
        "foo" : {
          "count" : 3
        },
        "s" : "abcde"
      }
    ]
  }
}

scala> incrementCount(json)
res1: io.circe.Json =
{
  "x" : {
    "y" : [
      0,
      1,
      {
        "s" : "abcde",
        "foo" : {
          "count" : 4
        }
      }
    ]
  }
}

[julien-truffaut]

I believe that as is not lawful because decoder is not injective e.g.

case class Point(x: Int, y: Int)

val decoder: Decoder[Point] = ...
decoder.decodeJson(obj("x" -> int(1), "y" -> int(2))) == decoder.decodeJson(obj("x" -> int(1), "y" -> int(2), "z" -> int(5))) 

[julien-truffaut]

You can upgrade monocle to 1.2.0-M2 and define a Plated instance

[travisbrown]

I'm going to merge this when it's green on the understanding that the JsonPath API is subject to change.

[dwijnand]

The readme brought me here ("We are likely to add an experimental optics subproject in 0.3.0"), so given this is merged I think the readme should be updated.