So what's an "empty" array anyway?

Currently, the constructs'{}'::arraytypeARRAY[]::arraytype
return zero-dimensional arrays, as does the underlying function
construct_empty_array().  I can't immediately find any way at SQL
level to produce an empty array with one or more dimensions.
However, construct_array and construct_md_array will happily build
zero-length arrays of dimension 1 or higher, leading to weirdnesses
such as illustrated here:
http://archives.postgresql.org/pgsql-general/2008-10/msg00915.php

Seems like we ought to clean this up.  I'm not sure which way to jump
though: should we decree that arrays of no elements must always have
zero dimensions, or should we get rid of that and standardize on, say,
1-D array with lower bound 1 and upper bound 0?

A somewhat related issue that I noticed while poking at this is that
array_dims() returns NULL for a zero-dimension array.  That seems a bit
bogus too; wouldn't an empty string be saner?  Of course the issue
goes away if we get rid of zero-dimension arrays.

Thoughts?
        regards, tom lane