Thanks to all for the pointer to #inspect and the behavior of #join in Ruby.
For some reason the possibility of using 'join' slipped my mind.  Python's
'join' requires the array to already be made of strings or else the effect
of a 'map/str' is required:

a=[1,2,3,4]

  ruby>  a.join(",")                     #->  "1, 2, 3, 4"
python>  string.join(map(str,a), ", ")   #->  "1, 2, 3, 4"

Interesting that Ruby does a #to_s on the elements of the array first.

But I noticed another oddity for nested arrays:

#join flattens the array!!

[[1,2],[3,4]].join(", ")   #-> "1, 2, 3, 4"

while #inspect works fine:

[[1,2],[3,4]].inspect      #-> "[[1, 2], [3, 4]]"

Given that Ruby has a #flatten is this the prefered/expected behavior of
#join ??  If we really wanted the current behavior of #join shouldn't we be
doing a.flatten.join(", ") ?

                                    * *

Too bad that such a crucial issue as exception raising for out-of-bounds
indexing in an array (or hash) got left out.  As, Dave suggests, I'm curious
to try overloading [], []= to see if/what breaks.

                                    * *

With reference to my own follow-up of my original posting.

When creating a sub-portion of an array that is not valid we get nil instead
of what i'd expect, an empty array, []

a=[1,2,3,4]
a[10]        #->  nil     OK, since there is no array bounds checking
             #            and concomittant exception raising in Ruby

But,

a[10..20]    #->  nil     instead of []

The problem is then that it looks like we can't iterate over an
a segment of an array that might not be valid:

e.g.,

i=10; j=20
for e in a[i..j]
   ...
end

It looks like either nil needs to have the 'each' method defined on it
or else the array segment should be [].  I really think a[i..j], a[i...j],
and a[i,cnt] should return [] for non-existing array segments.

Is there a Ruby idiom for dealing with this situation?
Should we really be explicitly checking our code for non-existing array
segments???

Thanks again.  (does seem to be nice friendly bunch on clr :-)

Raja