# 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