Example class 1 from Spot language: If/Else If/Else

class IfTheConditionTok

class IfTheConditionTok(Token):
  """If the condition x>4 is equal to true, follow these instructions:{}. 
	Else if the condition x<4 is equal to true, follow these instructions:{}. 
	Else, follow these instructions: {}."""

	def __init__(self, value = 0):
		self.value = value
		self.labelno = None
		self.condition = None
		self.true_block = None
		self.elseif_label = None
		self.elseif_cond = None
		self.elseif_block = None
		self.else_label = None
		self.else_block = None

	def statementd(self):
		global if_count
		advance(IfTheConditionTok)
		new_if_no = if_count
		self.labelno = "%d" %new_if_no
		if_count += 1
		new_condition = statement()
		self.condition = new_condition
		advance(CommaTok)
		advance(FollowTheseInstructionsTok)
		advance(ColonTok)
		advance(LCurlyTok)
		new_block = parse_block()
		self.true_block = new_block
		advance(RCurlyTok)
		advance(PeriodTok)
		if isinstance(token, ElseIfTok):
			advance(ElseIfTok) 
			self.elseif_label = "elseif_%d" % new_if_no
			new_condition = statement()
			self.elseif_cond = new_condition
			advance(CommaTok)
			advance(FollowTheseInstructionsTok)
			advance(ColonTok)
			advance(LCurlyTok)
			new_block = parse_block()
			self.elseif_block = new_block
			advance(RCurlyTok)
			advance(PeriodTok)
		if isinstance(token, ElseTok):
			advance(ElseTok)
			self.else_label = "else_%d" %new_if_no
			advance(CommaTok)
			advance(FollowTheseInstructionsTok)
			advance(ColonTok)
			advance(LCurlyTok)
			else_block = parse_block()
			self.else_block = else_block
			advance(RCurlyTok)
			advance(PeriodTok)				
		return self

	def eval(self, env):	
		if self.condition.eval(env) == True:
			print "\n>> The if condition is true -->executing if block"
			for statement in self.true_block:
				statement.eval(env)
		elif self.condition.eval(env) == False:
			print "\n>> The if condition is not true-->looking for else if or else"

			if (self.elseif_cond.eval(env) == True and self.elseif_block != None):
				print "\n>> Else if condition is true-->executing else if block"
				for statement in self.elseif_block:
					statement.eval(env)
			if (self.elseif_cond.eval(env) == False and self.else_block != None):
				print "\n>> The else if condition is not true-->executing else block"
				for statement in self.else_block:
					statement.eval(env)
			if (self.elseif_block == None and self.else_block != None):
				print "\n>> Previous conditions were not true-->Executing the else condition"
				for statement in self.else_block:
					statement.eval(env)

	def __repr__(self):
		return "(%s): self.condition = %s, self.true_block = %s, self.else_block = %s " %(self.__class__.__name__, self.condition, self.true_block, self.else_block)
	def codegen(self):
	
		commands = []

		# add if cond code
		if_cond_commands = self.condition.codegen()
		commands.extend(if_cond_commands)
		commands.append("POP EAX")

		# add dif jump comparisons --> if block
		if isinstance(self.condition, GreaterThanOpTok):
			commands.extend(["JG if_%s" % self.labelno]) #jump to ifblocklabel
		elif isinstance(self.condition, LessThanOpTok):
			commands.extend(["JL if_%s" % self.labelno])
		elif isinstance(self.condition, IsEqualToTok):
			commands.extend (["JE if_%s" % self.labelno])
		
		#add elseif cond code
		if self.elseif_block != None:
			elseif_cond_commands = self.elseif_cond.codegen()
			commands.extend(elseif_cond_commands)
			commands.append("POP EAX")

			#add dif jump comparisons --> else if block
			if isinstance(self.elseif_cond, GreaterThanOpTok):
				commands.extend(["JG %s" % self.elseif_label]) #jump to ifblocklabel
			elif isinstance(self.elseif_cond, LessThanOpTok):
				commands.extend(["JL %s" % self.elseif_label])
			elif isinstance(self.elseif_cond, IsEqualToTok):
				commands.extend (["JE %s" % self.elseif_label])

		#else block commands
		if self.else_block != None:
			#jump to else
			else_command = ["JMP %s" %self.else_label]
			commands.extend(else_command)

		#add true block code
		true_block = ["if_%s:" % self.labelno]
		for block in self.true_block:
			true_block.extend(block.codegen())
		true_block.extend(["JMP endif_%s" %self.labelno])
		commands.extend(true_block)

		#add else if true block
		if self.elseif_block!=None:
			else_if_block = ["%s:" %self.elseif_label]
			for block in self.elseif_block:
				else_if_block.extend(block.codegen())
			else_if_block.extend(["JMP endif_%s" %self.labelno])
			commands.extend(else_if_block)
		
		#add else true block
		if self.else_block!=None:
			else_block = ["%s:" %self.else_label]
			for block in self.else_block:
				else_block.extend(block.codegen())
			else_block.extend(["JMP endif_%s" %self.labelno])
			commands.extend(else_block)

		#end if
		commands.extend(["endif_%s:" %self.labelno])
		return commands