Opaque robot type

[byorgey]

Currently, all commands which need to identify a robot (e.g. install, give, reprogram) take a string identifying the robot by name. We also store robots by name internally in the robotMap. However, this has several disadvantages: it's not very type safe (for example, are you supposed to give "base" "tree" or give "tree" "base"? And if you misspell the name of a robot, it fails at runtime instead of typechecking time), and necessitates frequent, relatively costly string comparisons.

The basic idea is to add a new type robot which is opaque to the user but is internally represented by Int. Here are my current thoughts:

• Add a new base type robot.
• Change the type of any commands that currently take or return the name of a robot:
  • give : robot -> string -> cmd ()
  • install : robot -> string -> cmd ()
  • reprogram : robot -> cmd a -> cmd ()
  • build : cmd a -> cmd robot
• Note that robots can still have a name, which is displayed when they are viewed. But the name no longer needs to be unique.
• However, note that the build command doesn't take a name any more; in many cases players are probably fine with giving it a descriptive variable name (e.g. lambda_getter <- build get_lambda), but never plan to view it so don't really care what its "display name" is.
• However, we can add a command setname : string -> cmd () which lets a robot set its display name.
• Internally, we can add a new type of Value, VRobot :: Int -> Value. It can pretty-print as something like r105 or <105>, it doesn't really matter that much.
• What about robots that want to e.g. give something back to, say, the base? How can they get a reference to it? I propose adding a special variable parent : robot which is always a reference to a robot's parent (i.e. the robot that built it). So the code for building a robot to get you a thing might look like this:

  child <- build {move; thing <- grab; turn back; move; give parent thing}

  While we're at it we could also add a special global variable base : robot which is a reference to the base.

• We might also want to add a way to get the results of previous commands entered at the REPL, so if you did build and forgot to bind the result to something, it's not lost forever.

[polux]

What should parent return if the parent no longer exists? Should it return a handle to a non-existent robot or should it fail immediately?

[byorgey]

I think it would be safe to return a handle to a non-existent robot (but I could be convinced otherwise). We would just have to make sure that robot handles are never reused, but that should be easy.

[byorgey]

I don't think it should fail immediately if the parent doesn't exist. That would provide a way to instantly communicate a bit of information over any distance. =)

[xsebek]

I would also like to have some function for robots to detect each other in the wild - say meet : cmd (() + robot). :robot:

[byorgey]

Agreed! meet : cmd (() + robot) sounds great. I presume if there is more than one robot there, you just get an arbitrary one? Maybe later there could be a meetAll : cmd (list (robot)).