Given something like:

PRIMES=1 3 5 7 11
NUMBERS=1 2 3 4 5 6 7 8 9 10 11 12

I want to be able to refer to the elements of NUMBERS excluding those
of PRIMES.  Right now this can't be done - other than with a hideous
.for loop.  Expressions like:

echo "${NUMBERS:@n@$n is ${(${PRIMES:M$n} == ""):?not:} prime,@}"

don't work because ${PRIMES} is expanded to nothing before being
passed to the conditional logic - which insists on having a variable
reference and so chokes.   Also

echo "${NUMBERS:@n@$n is ${empty(${PRIMES:M$n}):?not:} prime,@}"

doesn't work either - not exactly sure why...

Of course the real reason I want this isn't for printing non-primes
;-)  But for avoiding cycles in auto-generated dependencies.

I can think of several approaches...

1. Allow something like:

   ${NUMBERS:${PRIMES:S,^,N,:ts}}

   Which would be treated as

   ${NUMBERS:N1:N3:N5:N...}

2. Make cond.c not require a variable reference for string
   comparisons.  This would allow:

   ${NUMBERS:@n@${("${PRIMES:M$n}" == ""):?$n:}@}

   to work.

3. Provide a means of saying "don't" expand yet, so that ${PRIMES:M$n}
   could be passed down to cond.c - or perhaps make that implicit if
   :? is present.

4. Make:

   ${PRIMES:M$n:?:$n}

   work as expected?  Ie. if ${PRIMES:M$n} is empty, then :? should
   eval false.

   
Thoughts? (on the above ;-)
--sjg