Commands to meet other robots

[byorgey]

This is an idea that came out of the discussion on #212 . The basic version would be to have a command like meet : cmd (() + robot) which gives you a reference to another robot in the same cell as you (or perhaps up to a certain distance away), if there is one. With lists (see #97 and #154), there could also be some kind of meetAll : cmd (list robot).

[byorgey]

Instead of a function that returns a list, we could have a function that lets you fold over the robots nearby. This is just as good as having a list but without requiring any special data structures. Something like meetAll : (robot -> b -> b) -> b -> cmd b, or maybe meetAll : (robot -> b -> cmd b) -> b -> cmd b.

[xsebek]

@byorgey I like the second meetAll that takes the function (robot -> b -> cmd b).

I take it will not be possible to use it with atomic? 😄

[byorgey]

@byorgey I like the second meetAll that takes the function (robot -> b -> cmd b).

Yes, I agree.

I take it will not be possible to use it with atomic? 😄

Haha, definitely not!

[byorgey]

I had almost convinced myself that the version with robot -> b -> b is better, but after playing with things for a while I'm convinced that the robot -> b -> cmd b version is superior.

• It is easy to implement the robot -> b -> b version in terms of the robot -> b -> cmd b version:

  def meetAllPure : (robot -> b -> b) -> b -> cmd b = \f. meetAll (\r. \b. return (f r b)) end
  

  Going the other direction is also possible but not as nice.
• The version with cmd will often be convenient when you want to run some command for each nearby robot, e.g. give each one a bitcoin:

  def makeItRain : cmd unit = meetAll (\r. \b. give r "bitcoin") () end
  

• The version with cmd is implicitly running the resulting commands in some particular order under the hood, but since it's going to iterate through the nearby robots in some arbitrary order anyway, you can't really complain about that.
• If you want complete control over the order in which the resulting commands get run or anything more fancy, you can always use b = cmd unit. (You just might have to throw in a call to join or two.)