Parser.py

import re

keywords = ['begin','define', 'print', 'if', 'update']
mathematic_operators = ['+','-','*','/','%','=']
comparison_operators = ['==','!=','<>','<=','>=''<','>']

def num_parser(data):
    match = re.match(r'\d+',data) or  re.match(r'-\d+',data)     # matches for numbers and returns a match object 
    if(match):
        return(int(data[:match.end()]), data[match.end():])

def space_parser(data):
    match=re.match(r'\s+',data)         # matches for white spaces and returns a match object 
    if(match):
        return([],data[match.end():])

def word_parser(data):
    match=re.match(r'[a-zA-Z_?]+',data)   # matches for string and returns a match object 
    if(match):
        return(data[:match.end()], data[match.end():])

def keyword_parser(data):               # matches for keywords 
    for keyword in keywords:
        if(data.startswith(keyword)):
            return(data[:len(keyword)],data[len(keyword):])

def mathematic_parser(data):
    for operator in mathematic_operators:
        if(data.startswith(operator)):
            return(data[:len(operator)],data[len(operator):])

def comparison_parser(data):
    for operator in comparison_operators:
        if(data.startswith(operator)):
            return(data[:len(operator)],data[len(operator):])

def comment_parser(data):
    if(data[0] == '#'):
        return(data[0],data[1:])

def parser(data):
    if(data[0]=='('):
        L=[]
        data=data[1:]   
        while(data[0]!=')'):
            output, data = parser(data)
            if(not output):
                continue
            else:
                L.append(output)
        return(L,data[1:])
    else:
        return(space_parser(data) or num_parser(data) or keyword_parser(data) or comment_parser(data) 
                                  or mathematic_parser(data) or comparison_parser(data) or word_parser(data))

#data="(begin (define circle_area (lambda r (* pi (* r r)))))"
#A,_ = parser(data)
#print(A)