[modified] minor semantics of state machines, added machinery to allow them to be nested more easily, added notes

state_machine.lua

@@ -12,6 +12,10 @@
 	on draw, the current state's draw callback is called
 
 	TODO: consider coroutine friendliness
+
+	TODO: consider refactoring the callback signatures to allow using objects with methods
+	      like update(dt)/draw() directly
+	      current pattern means they need to be wrapped (as in :as_state())
 ]]
 
 local path = (...):gsub("state_machine", "")
@@ -41,12 +45,27 @@ end
 --make an internal call
 function state_machine:_call(name, ...)
 	local state = self:_get_state()
-	if state and type(state[name]) == "function" then
+	if state then
-		return state[name](self, state, ...)
+		if type(state[name]) == "function" then
+			return state[name](self, state, ...)
+		elseif type(state) == "function" then
+			return state(self, name, ...)
+		end
 	end
 	return nil
 end
 
+--make an internal call and transition if the return value is a valid state
+--return the value if it isn't a valid state
+function state_machine:_call_and_transition(name, ...)
+	local r = self:_call(name, ...)
+	if self:has_state(r) then
+		self:set_state(r, r == self.current_state)
+		return nil
+	end
+	return r
+end
+
 -------------------------------------------------------------------------------
 --various checks
 
@@ -63,7 +82,7 @@ end
 
 --add a state
 function state_machine:add_state(name, data)
-	if self.has_state(name) then
+	if self:has_state(name) then
 		error("error: added duplicate state "..name)
 	else
 		self.states[name] = data
@@ -77,7 +96,7 @@ end
 
 --remove a state
 function state_machine:remove_state(name)
-	if not self.has_state(name) then
+	if not self:has_state(name) then
 		error("error: removed missed state "..name)
 	else
 		if self:in_state(name) then
@@ -99,13 +118,13 @@ function state_machine:replace_state(name, data, do_transitions)
 	end
 	self.states[name] = data
 	if do_transitions and current then
-		self:_call("enter")
+		self:_call_and_transition("enter")
 	end
 
 	return self
 end
 
---ensure a state doesn't exist
+--ensure a state doesn't exist; transition out of it if we're currently in it
 function state_machine:clear_state(name)
 	return self:replace_state(name, nil, true)
 end
@@ -113,23 +132,52 @@ end
 -------------------------------------------------------------------------------
 --transitions and updates
 
+--set the current state
+--if the enter callback of the target state returns a valid state name, then
+--	it is transitioned to in turn, and so on until the machine is at rest
 function state_machine:set_state(state, reset)
 	if self.current_state ~= state or reset then
 		self:_call("exit")
 		self.current_state = state
-		self:_call("enter")
+		self:_call_and_transition("enter")
 	end
 	return self
 end
 
 --perform an update
 --pass in an optional delta time which is passed as an arg to the state functions
+--if the state update returns a string, and we have that state
+--	then we change state (reset if it's the current state)
+--	and return nil
+--otherwise, the result is returned
 function state_machine:update(dt)
-	return self:_call("update", dt)
+	return self:_call_and_transition("update", dt)
 end
 
+--draw the current state
 function state_machine:draw()
 	self:_call("draw")
 end
 
-return state_machine
+--wrap a state machine in a table suitable for use directly as a state in another state_machine
+--upon entry, this machine will be forced into enter_state
+--the parent will be accessible under m.parent
+function state_machine:as_state(enter_state)
+	if not self._as_state then
+		self._as_state = {
+			enter = function(m, s)
+				self.parent = m
+				self:set_state(enter_state)
+			end,
+			update = function(m, s, dt)
+				return self:update(dt)
+			end,
+			draw = function(m, s)
+				return self:draw()
+			end,
+		}
+	end
+	return self._as_state
+end
+
+return state_machine