invocable all

procedure main(stk,ws:' \t')
    while write("-> ",read() ? (while (pos(0) & break stk)       |
        push(stk,numeric(x := (tab(upto(~ws)),tab(many(~ws)))\1) |
                 (p := proc(x,3|2|1))!getArgs(stk,args(p),[]) )  |
        break ["error"] )[1])
end

procedure getArgs(stk, i, a) # need args in reverse of stack order
    every 1 to i do push(a, pop(stk)|fail)
    return a
end