Mini Shell

# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.


def parse(s):
    s = s.strip()
    expr = []
    while s:
        if s[0:1] == b"(":
            newSexp = []
            if expr:
                expr[-1].append(newSexp)
            expr.append(newSexp)
            s = s[1:]
            continue
        if s[0:1] == b")":
            aList = expr.pop()
            s = s[1:]
            if not expr:
                assert not s
                return aList
            continue
        i = 0
        while s[i : i + 1].isdigit():
            i += 1
        assert i
        length = int(s[:i])
        data = s[i + 1 : i + 1 + length]
        expr[-1].append(data)
        s = s[i + 1 + length :]
    assert False, "this should not happen"


def pack(sexp):
    return b"".join(
        b"(%b)" % (pack(o),)
        if type(o) in (type(()), type([]))
        else b"%d:%b" % (len(o), o)
        for o in sexp
    )