parserfun.py

lex = Lexer()
lex['WS'] = regex.compile(r'\s+')
lex.ignore('WS')
lex['N'] = regex.compile(r'\d+')
for c in '+*()':
    lex[c] = c

class MathBuilder(Builder):
    """
    e.wrap -> t;
    e.add -> e + t;
    t.wrap -> f;
    t.mul -> t * f;
    f.lit -> N;
    f.paren -> ( e );
    """
    def wrap(self, x):
        return x
    def paren(self, _0, x, _1):
        return x
    def lit(self, n):
        return int(n.value)
    def add(self, a, _, b):
        return a + b
    def mul(self, a, _, b):
        return a * b

if __name__ == '__main__':
    parser = make_parser(SLR1, MathBuilder)
    for tok in lex.feed('1 + (2 * 3)', end=True):
        parser.feed(tok)
    print(parser.feed(EOF))