Recursive descent parser example

recursive-descent.py

class Literal(object):
    def __init__(self, c):
        self.literal = c
    def append(self, c):
        self.literal += c
    def __repr__(self):
        return ("<Literal '%s'>"  % self.literal)

class Nested(object):
    def __init__(self, children):
        self.children = children
    def append(self, child):
        self.children.append(child)
    def __repr__(self):
        return ("<Nested %s>" % self.children)

def parseinner(it):
    items = []
    for c in it:
        if c == '(':
            result,closed = parseinner(it)
            if not closed:
                pass # weird
            items.append(result)
        elif c == ')':
            return (Nested(items), True)
        else:
            if items and type(items[-1]) is Literal:
                items[-1].append(c)
            else:
                items.append(Literal(c))
    return (items, False)

def parse(s):
    it = iter(s)
    return parseinner(it)[0]


s = "foo(bar(baz))blim"  
print(parse(s))