from std import lib as stdlib

class Undefined:

	pass

def evaluate(node, context):

	if node is None:

		return None

	node_type = node["type"]

	if node_type == "Identifier":

		for ctx in reversed(context):

			if node["name"] in ctx:

				return ctx[node["name"]]

		return Undefined

	cls = node_index[node_type]

	obj = cls(node)

	return obj.eval(context)

class Program:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		program_context = [*context, dict()]

		for node in self.node["body"]:

			evaluate(node, program_context)

class ExpressionStatement:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		evaluate(self.node["expression"], context)

class CallExpression:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		callee = evaluate(self.node["callee"], context)

		arguments = [evaluate(arg, context) for arg in self.node["arguments"]]

		return callee(*arguments)

class MemberExpression:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		obj = evaluate(self.node["object"], context)

		prop = evaluate(self.node["property"], [obj])

		return prop

class BinaryExpression:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		left = evaluate(self.node["left"], context)

		right = evaluate(self.node["right"], context)

		# in fact this doesn't follow JavaScript "+" semantics

		if self.node["operator"] == "+":

			return left+right

		else:

			raise NotImplementedError

class EmptyStatement:

	def __init__(self, node):

		pass

	def eval(self, context):

		pass

class VariableDeclaration:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		for node in self.node["declarations"]:

			evaluate(node, context)

class VariableDeclarator:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		value = evaluate(self.node["init"], context)

		if self.node["id"]["type"] == "Identifier":

			name = self.node["id"]["name"]

			context[-1][name] = value

		else:

			raise NotImplementedError

class Literal:

	def __init__(self, node):

		self.node = node

	def eval(self, context):

		return self.node["value"]

node_index = {cls.__name__: cls for cls in [

	Program, ExpressionStatement, CallExpression, MemberExpression, EmptyStatement, BinaryExpression,

	VariableDeclaration, VariableDeclarator, Literal

]}

def interpret(parse_tree):

	return evaluate(parse_tree, [stdlib])

lib = {

	"document": {"write": print}

}