redef class FlowContext
	private var set_vars: Set[Variable] = new HashSet[Variable]

	private fun is_variable_set(variable: Variable): Bool
	do
		if self.set_vars.has(variable) then return true
		var previous = self.previous
		if previous.length == 0 then return false
		if previous.length == 1 then return previous.first.is_variable_set(variable)
		for p in self.previous do
			if not p.is_variable_set(variable) then
				return false
			end
		end
		# Cache the result
		self.set_vars.add(variable)
		return true
	end
end

redef class FlowContext
	# Store changes of types because of type evolution
	private var vars = new HashMap[Variable, nullable MType]

	# Adapt the variable to a static type
	# Warning1: do not modify vars directly.
	# Warning2: sub-flow may have cached a unadapted variable
	private fun set_var(v: TypeVisitor, variable: Variable, mtype: nullable MType)
	do
		if variable.declared_type == mtype and not variable.is_adapted then return
		if vars.has_key(variable) and vars[variable] == mtype then return
		self.vars[variable] = mtype
		v.dirty = true
		variable.is_adapted = true
		#node.debug "set {variable} to {mtype or else "X"}"
	end

	# Look in the flow and previous flow and collect all first reachable type adaptation of a local variable
	private fun collect_types(variable: Variable): Array[nullable MType]
	do
		#node.debug "flow for {variable}"
		var res = new Array[nullable MType]

		var todo = [self]
		var seen = new HashSet[FlowContext]
		while not todo.is_empty do
			var f = todo.pop
			if f.is_unreachable then continue
			if seen.has(f) then continue
			seen.add f

			if f.vars.has_key(variable) then
				# Found something. Collect it and do not process further on this path
				res.add f.vars[variable]
				#f.node.debug "process {variable}: got {f.vars[variable] or else "X"}"
			else
				todo.add_all f.previous
				todo.add_all f.loops
				if f.previous.is_empty then
					# Root flowcontext mean a parameter or something related
					res.add variable.declared_type
					#f.node.debug "root process {variable}: got {variable.declared_type or else "X"}"
				end
			end
		end
		#self.node.debug "##### end flow for {variable}: {res.join(" ")}"
		return res
	end
end