Parsing with ranges

[%u]

How to parse a simple format with ranges? For example a query string format:

string[string] params = parse("foo=1&bar=1%202&baz=1+2+3");
assert(params["foo"] == "1");
assert(params["bar"] == "1 2");
assert(params["baz"] == "1 2 3");

parse() should accept a string, an stream or anything else that make sense.

Thanks