(format stream
          ;; Are you ready for this one?
          "~:[{~;[~]~:{~S~:[->~S~;~*~]~:^ ~}~:[~; ~]~
           ~{~S->~^ ~}~:[~; ~]~[~*~;->~S~;->~*~]~:[}~;]~]"
          ;; Is that clear?
          ;; I omitted the sprintf-style arguments here - MJD
  )