1. Your problem is "var -s %r = $+(%r,$mid(%t,%a,1))", when it reaches a space in the string, $mid will evalutate to a space and your command will become "var -s %r = $+(%r, )". Obviously you cant $+ a space...
2. Not sure why "var -s $+(%,a,b) 1" does not work, as it works fine when using set -s (note: square braces around it dont help)
