on $*:TEXT:/^!chanlist$/iS:#:msg # I'm in: $regsubex($str(.,$chan(0)),/(.)/g,$chan(\n) $chr(32))

no need for $+()

on $*:TEXT:/^!chanlist$/iS:#: {
  var %i 1,%m
  while $chan(%i) { %m = %m $v1 | inc %i }
  msg # I'm in: %m
}