# Build and return a full AST.
	fun parse: Start
	do
		push(0, null)

		var lexer = _lexer
		loop
			var token = lexer.peek
			if token isa AError then
				return new Start(null, token)
			end

			var state = self.state
			var index = token.parser_index
			var action_type = parser_action(state, 2)
			var action_value = parser_action(state, 3)

			var low = 1
			var high = parser_action(state, 0) - 1

			while low <= high do
				var middle = (low + high) / 2
				var subindex = middle * 3 + 1 # +1 because parser_action(state, 0) is the length

				var goal = parser_action(state, subindex)
				if index < goal then
					high = middle - 1
				else if index > goal then
					low = middle + 1
				else
					action_type = parser_action(state, subindex+1)
					action_value = parser_action(state, subindex+2)
					break
				end
			end

			if action_type == 0 then # SHIFT
				push(action_value, lexer.next)
			else if action_type == 1 then # REDUCE
				_reduce_table[action_value].action(self)
			else if action_type == 2 then # ACCEPT
				var node2 = lexer.next
				assert node2 isa EOF
				var node1 = pop
				assert node1 isa AModule
				var node = new Start(node1, node2)
				node2.parent = node
				(new ComputeProdLocationVisitor(lexer.file.first_token)).enter_visit(node)
				return node
			else if action_type == 3 then # ERROR
				# skip injected tokens
				while not isset token._location do token = lexer.next
				var node2 = new AParserError.init_parser_error("Syntax Error: unexpected {token}.", token.location, token)
				var node = new Start(null, node2)
				return node
			end
		end
	end