define count_letters use $words
   { } as $wordHash    [ ] as $keys   [ ]  as $vals
   $words each chr
      dup $wordHash swap get 0 prefer 1 +   # stack: chr cnt
      swap $wordHash swap set
   $wordHash keys copy sort each
      dup $keys push
      $wordHash swap get $vals push
   $keys $vals combine  print "\n" print

"test.dat" as $file
$file read as $all_data
$all_data count_letters