case matching to element in array?

case matching to element in array?

[Phil Pennock]

I'm probably missing something really obvious here.  :^/  zsh-4.0.6.

As part of a shell function, I need to have one case occur if the
parameter matches an element in an array variable.  This can trivially
be done with if/else/endif.

I'm actually extending an existing function, which already uses "case"
and has several other situations handled.  Changing a dispatch-on-value
from "case" to "if" feels unclean.  I'll use an "if" for now, since I
need to get this done quickly, but I'm hoping there's a better method.

What am I missing in the following example?

-----------------------------< cut here >-------------------------------
function check {
	typeset -aU fred_list
	fred_list=(alpha beta gamma delta)

	case ${(L)1} in
		(foo)
			print Foo
			;;
		(${(j:|:)fred_list})
			print In List of Fred
			;;
		(*)
			print Default
			;;
	esac
}

% check foO
Foo
% check asdf
Default
% check beta
Default
-----------------------------< cut here >-------------------------------

Is there any way to construct the pattern for a case-match from a
variable?  Or is the pattern constructed, but the '|' splitting done
first, so that I'm ending up with a pattern with '|' in it?

If there's not a current method of doing this cleanly, then is it a
reasonable request to ask that the () matches in "case" statements be
extended to allow array contents, with an implicit '|' between the
elements of the array?  This would have the advantage of providing an
easy way to match on a string containing a '|', since you could do:

 set -A foo 'a|b'
 case $bar in
  ($foo) print ni ;;
 esac

which would avoid any need for special escaping.

At least, in the docs which I'm reading now, array-contents aren't
mentioned as a possibility and it doesn't seem to "work" as I describe.

If I've missed something, please enlighten me.

Thanks,
-- 
"We've got a patent on the conquering of a country through the use of force.
 We believe in world peace through extortionate license fees." -Bluemeat

Re: case matching to element in array?

[Peter Stephenson]

Phil Pennock wrote:
> What am I missing in the following example?
> 
> 		(${(j:|:)fred_list})

Change this to

                (${~${(j:|:)fred_list}})

to activate the `|'s.  The extra level of substitution seems to be
necessary to avoid the `|' in the (j:|:) having an effect too soon.

-- 
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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Re: case matching to element in array?

[Peter Stephenson]

Peter Stephenson wrote:
> Phil Pennock wrote:
> > What am I missing in the following example?
> > 
> > 		(${(j:|:)fred_list})
> 
> Change this to
> 
>                 (${~${(j:|:)fred_list}})
> 
> to activate the `|'s.  The extra level of substitution seems to be
> necessary to avoid the `|' in the (j:|:) having an effect too soon.

I worked out why I got confused before:  the canonical form is

                  (${(j:|:)~fred_list})

and I was putting the ~ before the (j:|:), which is why it wasn't
working.

-- 
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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Re: case matching to element in array?

[Bart Schaefer]

On Dec 5,  2:18pm, Peter Stephenson wrote:
} Subject: Re: case matching to element in array?
}
} I worked out why I got confused before:  the canonical form is
} 
}                   (${(j:|:)~fred_list})
} 
} and I was putting the ~ before the (j:|:), which is why it wasn't
} working.

Is there some reason why putting the tilde INSIDE the parens could not
be made to work as well?

    ${(j:|:~)fred_list} == ${(~j:|:)fred_list} == ${(j:|:)~fred_list}


-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Zsh: http://www.zsh.org | PHPerl Project: http://phperl.sourceforge.net   

Re: case matching to element in array?

[Peter Stephenson]

"Bart Schaefer" wrote:
> Is there some reason why putting the tilde INSIDE the parens could not
> be made to work as well?
> 
>     ${(j:|:~)fred_list} == ${(~j:|:)fred_list} == ${(j:|:)~fred_list}

Should be trivial to implement.  It's a historical oddity that `^', `~'
and `=' came before we had far more flags than could be accommodated
without some special syntax to mark them.

-- 
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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and/or privileged material. 
Any review, retransmission, dissemination or other use of, or
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