Re: Block comments ala Ray

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Sat, Feb 13, 2021 at 12:35 AM Stephane Chazelas
<stephane@xxxxxxxxxxxx> wrote:
>
> 2021-02-09 22:05:13 -0800, Bart Schaefer:
> [...]
> > !# This begins a block comment.
> > This is merely rambling.
> > This #! is the last line of the block
> [...]
>
> - those !#, #! look too much like a shebang.

Which actually doesn't matter, because #! isn't special anywhere but
the first line.

> - !# is already histsubst syntax.

Also doesn't matter, this was intended only to operate where history
is disabled anyway.

> - It's also the !# extendedglob

You mean "zero or more occurrences of '!' "?  This is another reason I
was only allowing "!#" at the start of a line.  Under what
circumstances would you begin a new line with that glob?

> - It's also (POSIXly) invoking the !# command.

Yes, I mentioned that.  It seems pretty damn unlikely to use that, as
it has no effect other than to set $? to 1.

> Also consider
>   scripts that do:
>
>   cat > script <<EOF
>   #! /bin/sh -
>   ...
>   EOF
>
>   making it difficult to comment out those codes

That one has some relevance, and argues for requiring #! to be
followed immediately by a newline, if not also preceded by one.

> - syntax is a bit obscure and uncommon.

Intentionally so, yes.  It has to be something that would essentially
never appear in an existing script.

>   Would we allow blanks
>   before the !# for indentation purposes.

No.

>   Would those !# be
>   recognised if the previous line ends in a \ or inside
>   heredocs?

No, because it's handled by the lexer.  It's not recognized anywhere
any other comment isn't.

>   Does it have to be delimited with whitespace? Can we
>   use !########### .. ##############!? That ! is easy to miss.

Those are among the reasons I didn't think forming "inline comments"
was a good idea.

>   Would we allow escaping the closing #!? How?

No, because you can't escape anything inside a comment.

> - assuming we allow nesting (which would be useful to comment
>   out sections of code that contain block comments),

I hadn't considered nesting.  You can't nest C /* ... */ comments, and
this was not intended to work any differently.

> - <<# .. #>> allows inline comments, but looks more like a
>   redirection operator than a comment.

That's why I rejected <# ... #>.

> To me, there are more useful features that could be added to zsh
> before that one.

This is like saying we should solve problems on earth before we spend
money on space exploration.  It's a false dichotomy.

> Or ksh's <#((...)), <#.. <>;  redirection operators.

The possibility of wanting to add those would also argue against using
"<#" or "<<#" as a comment introducer.