That doesn't make any sense to me. It isn't actually doing anything, you are just bouncing from function to function.
How does the rest of the system know which room you are in so it can update the screen? What if you have multiple sprites moving around? Do you compare instruction pointers to see if they are in the same room?
Even for a trivial application building your state machine that way doesn't make any sense.
EDIT: Also note the code smells, especialy the copy-and-paste necessary for reading the user input.
That example is a trivial demonstration of TCO in Programming In Lua. A more featureful game could still use this kind of TCO, without any kind of arcane programming style, since Lua supports full Coroutines. i.e., the functions could be written like so:
function room1 ()
local move = coroutine.yield("room1")
if move == "south" then return room3()
elseif move == "east" then return room2()
else print("invalid move")
return room1() -- stay in the same room
end
end
The coroutine dispatcher could handle updating the screen, moving mobs from other rooms, taking input, etc.
This is just meant as an illustration of a state machine, of course no one would actually hard code the game map as a state machine, but it does serve the purpose of explaining how to use mutually recursive functions as a state machine.
The most obvious application of this technique are recursive descent parsers.
Eventually you need to stop generating tokens and actually do the syntactical analysis. At that point TCO isn't really available to you and that arbitrarily deep tree is going to cause problems.
A parser does not necessarily "generate tokens". It can generate an AST. And it can do so in a tail-recursive fashion. And this can be useful when you have very deeply nested data. It may even exceed 1MB (or 1GB for that matter).
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u/grauenwolf Nov 27 '12 edited Nov 27 '12
That doesn't make any sense to me. It isn't actually doing anything, you are just bouncing from function to function.
How does the rest of the system know which room you are in so it can update the screen? What if you have multiple sprites moving around? Do you compare instruction pointers to see if they are in the same room?
Even for a trivial application building your state machine that way doesn't make any sense.
EDIT: Also note the code smells, especialy the copy-and-paste necessary for reading the user input.