CODE EXAMPLE FOR PYTHON

create programming language in python

from sly import Parser

class BasicParser(Parser):
	#tokens are passed from lexer to parser
	tokens = BasicLexer.tokens

	precedence = (
		('left', '+', '-'),
		('left', '*', '/'),
		('right', 'UMINUS'),
	)

	def __init__(self):
		self.env = { }

	@_('')
	def statement(self, p):
		pass

	@_('var_assign')
	def statement(self, p):
		return p.var_assign

	@_('NAME "=" expr')
	def var_assign(self, p):
		return ('var_assign', p.NAME, p.expr)

	@_('NAME "=" STRING')
	def var_assign(self, p):
		return ('var_assign', p.NAME, p.STRING)

	@_('expr')
	def statement(self, p):
		return (p.expr)

	@_('expr "+" expr')
	def expr(self, p):
		return ('add', p.expr0, p.expr1)

	@_('expr "-" expr')
	def expr(self, p):
		return ('sub', p.expr0, p.expr1)

	@_('expr "*" expr')
	def expr(self, p):
		return ('mul', p.expr0, p.expr1)

	@_('expr "/" expr')
	def expr(self, p):
		return ('div', p.expr0, p.expr1)

	@_('"-" expr %prec UMINUS')
	def expr(self, p):
		return p.expr

	@_('NAME')
	def expr(self, p):
		return ('var', p.NAME)

	@_('NUMBER')
	def expr(self, p):
		return ('num', p.NUMBER)


class BasicExecute:
	
	def __init__(self, tree, env):
		self.env = env
		result = self.walkTree(tree)
		if result is not None and isinstance(result, int):
			print(result)
		if isinstance(result, str) and result[0] == '"':
			print(result)

	def walkTree(self, node):

		if isinstance(node, int):
			return node
		if isinstance(node, str):
			return node

		if node is None:
			return None

		if node[0] == 'program':
			if node[1] == None:
				self.walkTree(node[2])
			else:
				self.walkTree(node[1])
				self.walkTree(node[2])

		if node[0] == 'num':
			return node[1]

		if node[0] == 'str':
			return node[1]

		if node[0] == 'add':
			return self.walkTree(node[1]) + self.walkTree(node[2])
		elif node[0] == 'sub':
			return self.walkTree(node[1]) - self.walkTree(node[2])
		elif node[0] == 'mul':
			return self.walkTree(node[1]) * self.walkTree(node[2])
		elif node[0] == 'div':
			return self.walkTree(node[1]) / self.walkTree(node[2])

		if node[0] == 'var_assign':
			self.env[node[1]] = self.walkTree(node[2])
			return node[1]

		if node[0] == 'var':
			try:
				return self.env[node[1]]
			except LookupError:
				print("Undefined variable '"+node[1]+"' found!")
				return 0

              
if __name__ == '__main__':
	lexer = BasicLexer()
	parser = BasicParser()
	print('GFG Language')
	env = {}
	
	while True:
		
		try:
			text = input('GFG Language > ')
		
		except EOFError:
			break
		
		if text:
			tree = parser.parse(lexer.tokenize(text))
			BasicExecute(tree, env)