HELP POPPRINT                                         JLCunningham, July 1982

The library file LIB POPPRINT provides a pretty-printer for lists which
consist of POP program, i.e. the sort of list that can be successfully
*POPVALed (see the example at the end of this help file). The list is printed
in a form which can be re-read or compiled, e.g. strings are printed with
string quotes.

The simplest use, using all the defaults, is to make successive calls to the
procedure POPPRINT with lists to be pretty-printed. The last item in the list
of the last call should be *TERMIN. The output is written to a VED buffer
called 'program.p', e.g.

    lib popprint;
    popprint([define foo(x,y); x*y enddefine;]);
    popprint(['Finished'=>]);
    popprint([^termin]);
    ved program.p;

-- CHANGING DEFAULTS --------------------------------------------------------

The algorithm used is heuristic; in particular it is table-driven (using the
variables SPACETABLE, BREAKLINEBEFORE, and BREAKLINEAFTER) and does not do any
parsing. Procedures and variables provided by the library are:

PRSTRING          print a string with string quotes

SPACETABLE        a boolean table providing heuristic information for the
                  pretty-printer, to decide when not to omit spaces between
                  items.

BREAKLINEBEFORE   a list of POP items which should start a new line of output

BREAKLINEAFTER    a list of POP items which come at the end of a line of output

POPPRINTOUT       a variable containing the character consumer to be used by
                  POPPRINT. It will normally be initialised by a call of
                  STARTPOPPRINT when POPPRINT is first used. The default writes
                  to a ved buffer called 'program.p': see STARTPOPPRINT. If
                  a character consumer produced by DISCOUT is assigned to
                  POPPRINTOUT, then the output file will not be justified, i.e.
                  there will be no indentation.

STARTPOPPRINT     takes a filename as argument (if the filename is a
                  word '.p' will be added), and uses lib vedout to produce a
                  character consumer to be assigned to POPPRINTOUT. So if you
                  want to send output to a differently named ved buffer, call
                  STARTPOPPRINT before the first call of POPPRINT.

POPPRINT          takes a list as argument, and pretty-prints it as POP code to
                  the character consumer POPPRINTOUT. If POPPRINTOUT is false,
                  then STARTPOPPRINT is called prior to any printing with
                  'program.p' as argument.

-- EXAMPLE TO ILLUSTRATE COMPLETELY RE-WRITING A FILE -----------------------

The current heuristics tend to result in lines which are longer than 80
columns; this could possibly look nicer when printed on 132-column paper.
The following would re-write a file (with a different name):

    lib popprint;
    startpopprint('name2.p');
    popprint(pdtolist(incharitem(discin('name1.p'))));
    popprint([^termin]);

When the above code has been executed, there will exist a VED buffer called
NAME2.P containing the re-written file; it will not however have been written
to disc. The buffer can, however, be edited, written etc. as required
(although this is probably not worth doing, since comments and blank lines
will get lost).

See also
HELP *PRINT - for other printing procedures
REF  *SYSIO - for more information on I/O procedures