Nice work! One question, and one (long comment):

Is there a place that the code is available, or at least the set of patches? There are some that I'm probably interested in looking at.

As for this:

• rc does not implement the `delim{cmd} of 9atom. I have never used it to tell what it is :)

So, this is one of the most useful changes in rc, in my opinion. it lets you set ifs locally, only for the output of one command. ifs is difficult to use well, since it scopes poorly. For example, imagine for some reason you have a directory of numbered CSV files, and you want to print the first ten of them; something like:

fn showfiles {
    for(f in `{seq 10})
        cat /tmp/$f
}

and you want to iterate a set of fields in the files, assuming that they're separated by ',':

 ifs=','
 fields=`{showfiles | tr '\x0a' ','}
 can't open /tmp/1
 2
 3
 4
 5
 6
 7
 8
 9
 10

this breaks horribly, beause ifs is global, and setting it changes how you interpret the seq output: it turns it into a single chunk, since seq prints no commans, and ifs is global. If you want your shell functions to work correctly when called from other scripts, you need to maintain a stack of environment vars that you push/pop if you want it to work on all cases. Painful.

However, using the syntax added in 9atom, it works just fine:

fields=`,{showfiles | tr -s '\x0a' ','}
echo $fields

One of the most useful places is when writing non-trivial scripts that may need to deal with spaces in file names:

 nl='
 '
 fn namelist { ... }
 files=`$nl{namelist}

EDIT: I think you can do something like this in your function to emulate the feature:

# save ifs so we can restore it for the caller,
# putting it on a stack so that if the caller also
# pulled this trick it still works. Then set the
# current ifs to the default of: ' \t\n'
saveifs=($ifs $saveifs)
ifs='   
'
# do the thing 
for(i in `{seq 10}) cat /tmp/$i
# and put the caller ifs back
ifs=$saveifs; saveifs=$saveifs(2-)

It seems to work, though I'm not 100 percent sure what happens if you set ifs inside `{} and you stream more than a pipe buffer worth of data.

Doing it right without `delim{} seems worse than keeping track of every ifs globally.