binding a reference to a variable

[Christian Tanzer]

Andrew Koenig <ark at research.att.com> wrote:

> The point of this example is the . operator, which takes a pattern
> (by value) as its left argument and a variable (by reference) as its
> right argument.  The result is a pattern that matches the same strings
> as the left argument, but if the match is successful, it assigns
> the substring matched to the variable that is the right argument.
>
> As it happens, I can implement much the same idea in C++, though
> the exact details of operator overloading make it look somewhat
> different:
>
>     string id, domain;
>     match(name, pos(0) + (break("@") >> id) + "@" + (rpos(0) >> domain));
>
> and I can also implement a similar idea in ML, though I don't
> think it's worth going into details here.
>
> So I was thinking about how I would do something similar in Python.
>
> Focusing just on the  (break("@") . id)  subexpression, how would
> one implement it?  That's what led me on this path.

How about using a class to implement the matcher and assigning the
matched substrings to a namespace provided by the matcher instance in
question?

Using `* args, ** kw` trickery, you might be able to trade readability
of the matcher code for ease of the matcher clients. For instance:

    m(name, m.pos(0) + m.break(id="@") + "@" + m.rpos(domain=0))

YMMV,

-- 
Christian Tanzer                                         tanzer at swing.co.at
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