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Re: Pattern matching lines starting with double comment characters

From: Greg Wooledge
Subject: Re: Pattern matching lines starting with double comment characters
Date: Sun, 26 Feb 2023 08:34:55 -0500

On Sun, Feb 26, 2023 at 08:57:18PM +0900, Koichi Murase wrote:
> 2023年2月26日(日) 17:02 Tapani Tarvainen <>:
> > > The only portable way is to specify each just the same as you do for //:
> > >
> > > pn_ere = "^[[:space:]]*(##|;;|!!|@c|//)[[:space:]]+"
> >
> > Yes. Assuming the intent is to allow exactly two of the comment
> > characters. Which the OP apparently wanted, but at least offhand
> > I can't think of any language that requires blank space after
> > the comment marker and it is actually rather common to use
> > more of them at times.
> To me, the OP's question is clear enough about the double comment
> characters, and it does not feel so strange.  Rather, generalizing it
> to an arbitrary number of comment characters seems strange.  I naively
> wonder what would be the use case for detecting an arbitrary number of
> comment characters.

The thing is, this is at least the *third* thread started pertaining
to whatever this project is.  Here are the first two, that I know of:

In the first message of the first thread, there is a regex that
looks for [#;!]+ among other things.  So, the original precedent was
to look for an arbitrary number of leading comment markers.

At the same time, however, we were given examples that showed exactly
two ## characters.  I believed, at the time, that the author had
cargo-culted the regex from some random source, and was trying to
wedge it into his own project, where it was simply not needed.

But then the requirements kept changing, and changing, and changing.
The only thing that was clear was that all the examples we had been
given fell *completely* short of describing the expected inputs.

After a few iterations, I simply gave up.  We're clearly never going to
be given the actual requirements, all at once, so that we can craft a
working solution.  Anything we do will be invalidated by the next change.

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