From: "Jörg W Mittag" <JoergWMittag+Ruby@...>
Date: 2010-09-29T09:10:15+09:00
Subject: Re: puts and return

Rick DeNatale wrote:
> No, the only difference between && and 'and' is their parsing precedence.
> 
> And nearly every time I've seen and used instead of && I've found a bug.

I use it sometimes for control flow in DSL-ish situations. Here's a
line from a toy recursive descent parser:

    @sign *= -1 if lookahead == '-' and consume

Here, I use `and` specifically as a way to denote control flow. I
agree that encountering a line like this somewhere in the middle of a
generic codebase is very surprising and often puzzling, but in this
case it is a highly stylized codebase with its own idioms.

For example, that same parser also contains the line

    while parse_digit; end

or this one

    parse_string or parse_array

Again, I would *never* write something like this in generic code, but
in this particular case it is my specific idiom to encode the EBNF
rules

    string | digit

and

    digit*

This allows me to distinguish between infrastructure code that is
there to support the parser, and the actual parsing rules themselves,
since the former *always* uses parentheses, `&&`, `||` and `!` and the
latter always uses `and`, `or` and `not` and doesn't use parentheses.

jwm