Allow array-like pair dereferencing

[cjllanwarne]

As mentioned a couple of times, the pair dereferencing is not intuitive (you have to look it up in the docs to be able to find it). Perhaps we could additionally support array-style dereferencing?

Pair[Int, Int] p = (100, 22)
Int one_hundred = p[0]
Int twenty_two = p[1]

[patmagee]

I like this approach better than the .left and .right way tbh. To me, this is more consistent with a two element tuple, whereas left/right are not really used anywhere else in the wild for referencing somehting that even remotely looks like a pair

[cjllanwarne]

@patmagee if we do this, a more intuitive json input might be a good idea too- do you have any thoughts on what that might look like? Right now it's:

{
  "pair": {
    "left": 100,
    "right": 22
  }
}

[patmagee]

@cjllanwarne The One thing I DO like about pair is that it differentiates itself from an array type, however it could be interpreted as a fancy map like type.

One way would be the simplest, which would be a 2 element Array

{
   "pair": [ 100, 22 ]
}

this is similar to the Pair-literal of (100,22)

[geoffjentry]

left/right always struck me as being too tied to Scala's Either (where I also dislike the left/right terminology).

[jdidion]

Related to #279. But I wouldn't mind either pair[0], pair[1] or pair.0, pair.1. Would still continue to support left and right.