macro 
    /usr/local/lib/janet/spork/test.janet  on  line  77 , column  1 
    (timeit-loop  head  &  body )
    Similar  to  `loop` , but  outputs  performance  statistics  after  
    completion.  Additionally  defines  a  `:timeout`  verb  to  iterate  
    continuously  for  a  given  number  of  seconds.  If  the  first  form  of  
    `body`  is  a  bytes , it  will  be  taken  as  a  custom  tag.