from list_stack import Stack

"""Various stack applications"""

def is_valid_source( srcfile ):
    """Check to see if the pairs in source code are valid"""
    s = Stack() 
    for line in srcfile :
        for token in line :
            if token in "{[(" :
                s.push( token )
            elif token in "}])" :
                if s.is_empty() :
                    return False
                else :
                    left = s.pop()
                    if (token == "}" and left != "{") or \
			 (token == "]" and left != "[") or \
			 (token == ")" and left != "(") :
                        return False
			   
    return s.is_empty() 

f = open('c_source.txt', 'r')
text = f.read()
print('check to see if source is valid : ', is_valid_source(text))