[Groff] improved hpf request

[Werner LEMBERG]

Dear friends,


as mentioned earlier on this list, distributing a modified version of
Knuth's `hyphen.tex' is a copyright violation.  To fix this, I've
improved the `hpf' request to read many (but not all) of TeX's
hyphenation patterns unmodified.  From groff_diff.7:

       .hpf file
              Read  hyphenation  patterns from file; this will be
              searched for in the  same  way  that  name.tmac  is
              searched  for  when the -mname option is specified.
              It should have the same format as (simple) TeX pat­
              terns  files.   More  specifically,  the  following
              scanning rules are implemented.

              ·      A percent sign starts a comment (up  to  the
                     end of the line) even if preceded by a back­
                     slash.

              ·      No support for `digraphs' like \$.

              ·      The only multi-character construction recog­
                     nized  is  ^^xx (x is 0-9 or a-f); other use
                     of ^ causes an error.

              ·      No macro expansion.

              ·      hpf checks for the expression \patterns{...}
                     (possibly  with  whitespace before and after
                     the braces).  Everything between the  braces
                     is  taken  as  hyphenation patterns.  Conse­
                     quently, { and } are  not  allowed  in  pat­
                     terns.

              ·      Similarly, \hyphenation{...} gives a list of
                     hyphenation exceptions.

              ·      \endinput is recognized also.

              ·      For backwards compatibility, if \patterns is
                     missing, the whole file is treated as a list
                     of hyphenation  patterns  (only  recognizing
                     the  % character as the start of a comment).

              Use the hpfcode request to map the encoding used in
              hyphenation  patterns files to groff's input encod­
              ing.

              The set of hyphenation patterns is associated  with
              the  current  language set by the hla request.  The
              hpf request is usually invoked by the troffrc file;
              a  second  call  replaces the old patterns with the
              new ones.

And here the description of the new hpfcode request:

       .hpfcode a b c d ...
              After reading a hyphenation patterns file with  the
              hpf  or  hpfa  request, convert all characters with
              character code a in the recently read  patterns  to
              character code b, character code c to d, etc.  Ini­
              tially, all character codes map to themselves.  The
              arguments  of hpfcode must be integers in the range
              0 to 255.  Note that it is  even  possible  to  use
              character  codes  which are invalid in groff other­
              wise.

Here an example for Danish.

  .hla dansk
  .
  .\" for the file dkspecial.tex
  .hpfcode 88 230 \" X æ
  .hpfcode 89 248 \" Y ø
  .hpfcode 90 229 \" Z å
  .
  .hcode Æ æ  æ æ
  .hcode Ø ø  ø ø
  .hcode Å å  å å
  .
  .hpf  dkcommon.tex
  .hpfa dkspecial.tex
  .
  .
  .ll 1.3i
  .hla us
  The phrase \[lq]See also\[rq] means
  .hla dansk
  \[lq]Se også\[rq]
  .hla us
  in Danish.

The result with the latin1 device:

  The    phrase
  "See    also"
  means "Se og­
  så"  in  Dan­
  ish.

Please test and enjoy!


    Werner