Re: PATCH: `try' syntax

[Peter Stephenson <pws@csr.com>]

Bart Schaefer wrote:
> * A "shortloops" form "try { ... }" might be nice, or maybe should be the
> only form.

It's rather nonstandard.

> * How about making this work with any loop body by replacing "do" with
> "try"?  Then get rid of "try" as a standalone reserved word and instead
> use "repeat 1; try ... always ... done"

That's mixing up the syntax in exactly the way I wanted to avoid.
I wanted the `try' bit to be separate so that it was clear what
was going on.

> * Rather than putting colons or some other unlikely character in front of
> the name, use plain words and start with them "disable"d, so that in order
> to use this syntax one must first "enable -r try always tried".  (This
> technique could apply to other extension syntax as well.)

Yes, it's interesting, but the problem with functions is difficult.
An extra flag to autoload could specify extended syntax.

> * Tangential thought: Is it really necessary to disable e.g. both "case"
> and "esac" or is it sufficient to disable (and enable) "case"?

Currently you do need to disable both.

> So does that mean that
> 
>    :try
>      setopt errexit
>      false
>      print not reached 1
>    :always
>      print reached
>    :tried
>    print not reached 2
> 
> prints only "reached"?  Then that's a non-obvious way to accomplish what
> Oliver wanted:
> 
> > > It'd be really useful to have a way to skip over the rest of the try
> > > block, going straight to the always code.

You'd need to use errreturn, since exit is immediate.  Otherwise
it works.

Oliver wrote:
> Or, thinking along those lines, you could use something like
> { ... } always { ... }
> That currently finds a syntax error at always.

This is definitely an interesting suggestion...

Syntactically, it's still a bit tricky.  Either `always' is a keyword,
or it isn't.  If it is it generates a syntax error when used elsewhere.
If it isn't, we have to convert the string into a token in this one
case.  Maybe that's not so hard, though.

The other part is that we don't know till we get to the `always'
whether there is an always present.  Possibly it could just be
tacked onto ordinary current-shell structures.

As things stand I'm not sure I'm going to have any free time before
2008, but if I do is this worth trying?  (In other words, is it
reasonably agreeable to everyone interested?)

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 692070


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