fcn range(ns){
   fcn(w){
      if (w.atEnd) return(Void.Stop);
      a:=b:=w.next(); n:=0;
      while(b+1 == (c:=w.peekN(n))){ n+=1; b=c }
      if(n>1){do(n){w.next()}; return("%d-%d".fmt(a,b)); }
      a
   } :
   (0).pump(*,List,_.fp(ns.walker().tweak(Void,Void))).concat(",");
}