function 
    /usr/local/lib/janet/spork/misc.janet  on  line  529 , column  1 
    (merge-sorted  a  b  &opt  <? )
    Merges  two  sorted  arrays  so  that  the  result  remains  sorted , using  
    an  optional  comparator.  If  no  comparator  is  given , `<`  is  used.