Christian Soeller > PDL-2.4.3 > PDL::Doc



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PDL::Doc - support for PDL online documentation


  use PDL::Doc;
  $onlinedc = new PDL::Doc ($docfile);
  @match = $onlinedc->search('m/slice|clump/');


An implementation of online docs for PDL.

PDL documentation conventions ^

For a package like PDL that has a lot of functions it is very desirable to have some form of online help to make it easy for the user to remind himself of names, calling conventions and typical usage of the multitude of functions at his disposal. To make it straightforward to extract the relevant information from the POD documentation in source files that make up the PDL distribution certain conventions have been adopted in formatting this documentation.

The first convention says that all documentation for PDL functions appears in the POD section introduced by

  =head1 FUNCTIONS

Individual functions in this section are introduced by

  =head2 funcname

where signature is the argumentlist for a PP defined function as explained in PDL::PP. Generally, PDL documentation is in valid POD format (see "perlpod") but uses the =for directive in a special way. The =for directive is used to flag to the PDL Pod parser that information is following that will be used to generate online help.

The PDL podparser is derived from the PDL::Pod::Parser class that had to be patched in a few places, partly to fix minor bugs, partly to enhance functionality for perusal by PDL::Doc. Since the PDL::Doc module is still experimental the patched Pod-Parser distribution is included with the current PDL-Doc distribution. Note that PDL::Doc will not work correctly with the released Pod-Parser distribution.

The PDL Pod parser recognises the following =for directives:


indicates that the one line reference for this function follows, e.g.,

   =for ref

   Returns a piddle of lags to parent.

the signature for the current function follows, e.g.,

   =for sig

      Signature: (a(n), [o]b(), [t]tmp(n))

an indication of the possible calling conventions for the current function, e.g.,

   =for usage

      wpic($pdl,$filename[,{ options... }])

lists options for the current function, e.g.,

   =for options

      CONVERTER  => 'ppmtogif',   # explicitly specify pbm converter
      FLAGS      => '-interlaced -transparent 0',  # flags for converter
      IFORM      => 'PGM',        # explicitly specify intermediate format
      XTRAFLAGS  => '-imagename iris', # additional flags to defaultflags
      FORMAT     => 'PCX',        # explicitly specify output image format
      COLOR      => 'bw',         # specify color conversion
      LUT        => $lut,         # use color table information

gives examples of typical usage for the current function:

   =for example

       wpic $pdl, $file;
       $im->wpic('web.gif',{LUT => $lut});
       for (@images) {
         $_->wpic($name[0],{CONVERTER => 'ppmtogif'})

provides information on how the function handles bad values (if $PDL:Config{WITH_BADVAL} is set to 1). The intention is to have this information automatically created for pp-compiled functions, although it can be over-ridden.

The PDL podparser is implemented as a simple state machine. Any of the above =for statements switches the podparser into a state where the following paragraph is accepted as information for the respective field (Ref, Usage, Opt, Example or Bad). Only the text up to the end of the current paragraph is accepted, for example:

  =for example

         ($x,$y) = $a->func(1,3);  # this is part of the accepted info
         $x = func($a,0,1);        # this as well

         $x = func($a,$b);         # but this isn't

To make the resulting pod documentation also easily digestible for the existing pod filters (pod2man, pod2text, pod2html, etc) the actual textblock of information must be separated from the =for directive by at least one blank line. Otherwise, the textblock will be lost in the translation process when the "normal" podformatters are used. The general idea behind this format is that it should be easy to extract the information for online documentation, automatic generation of a reference card, etc but at the same time the documentation should be translated by the standard podformatters without loss of contents (and without requiring any changes in the existing POD format).

The preceding explanations should be further explained by the following example (extracted from PDL/IO/Misc/misc.pd):

   =head2 rcols()

   =for ref

   Read ASCII whitespaced cols from file into piddles efficiently.

   If no columns are specified all are assumed
   Will optionally only process lines matching a pattern.
   Can take file name or *HANDLE.

   =for usage

    Usage: ($x,$y,...) = rcols(*HANDLE|"filename", ["/pattern/",$col1, $col2,] ...)


   =for example

     ($x,$y)    = rcols 'file1'
     ($x,$y,$z) = rcols 'file2', "/foo/",3,4
     $x = PDL->rcols 'file1';

   Note: currently quotes are required on the pattern.

which is translated by, e.g, the standard pod2text converter into:


    Read ASCII whitespaced cols from file into piddles efficiently.

    If no columns are specified all are assumed Will optionally only
    process lines matching a pattern. Can take file name or *HANDLE.



      ($x,$y)    = rcols 'file1'
      $x = PDL->rcols 'file1';

    Note: currently quotes are required on the pattern.

It should be clear from the preceding example that readable output can be obtained from this format using the standard converters and the reader will hopefully get a feeling how he can easily intersperse the special =for directives with the normal POD documentation.

Which directives should be contained in the documentation

The module documentation should start with the

  =head1 NAME

  PDL::Modulename -- do something with piddles

section (as anyway required by pod2man) since the PDL podparser extracts the name of the module this function belongs to from that section.

Each function that is not only for internal use by the module should be documented, introduced with the =head2 directive in the =head1 FUNCTIONS section. The only field that every function documented along these lines should have is the Ref field preceding a one line description of its intended functionality (suitable for inclusion in a concise reference card). PP defined functions (see PDL::PP) should have a Sig field stating their signature. To facilitate maintainance of this documentation for such functions the 'Doc' field has been introduced into the definition of pp_def (see again PDL::PP) which will take care that name and signature of the so defined function are documented in this way (for examples of this usage see, for example, the PDL::Slices module, especially slices.pd and the resulting Similarly, the 'BadDoc' field provides a means of specifying information on how the routine handles the presence of bad values: this will be autpmatically created if BadDoc is not supplied, or set to undef.

Furthermore, the documentation for each function should contain at least one of the Usage or Examples fields. Depending on the calling conventions for the function under consideration presence of both fields may be warranted.

If a function has options that should be given as a hash reference in the form

   {Option => Value, ...}

then the possible options (and aproppriate values) should be explained in the textblock following the =for Opt directive (see example above and, e.g., PDL::IO::Pic).

It is well possible that some of these conventions appear to be clumsy at times and the author is keen to hear of any suggestions for better alternatives.



  $onlinedc = new PDL::Doc ('file.pdl',[more files]);


add another file to the online database associated with this object.


set the name of the output file for this online db


Make sure that the database is slurped in


save the database (i.e., the hash of PDL symbols) to the file associated with this object.


Return the PDL symhash (e.g. for custom search operations)


Search a PDL symhash

  $onldc->search($regex, $fields [, $sort])

Searching is by default case insensitive. Other flags can be given by specifying the regexp in the form m/regex/ismx where / can be replaced with any other non-alphanumeric character. $fields is an array reference for all hash fields that should be matched against the regex. Valid fields are

  Name,    # name of the function
  Module,  # module the function belongs to
  Ref,     # the one-line reference description
  Example, # the example for this function
  Opt,     # options
  File,    # the path to the source file this docs have been extracted from


Scan a source file using the PDL podparser to extract information for online documentation


Scan whole directory trees for online documentation in .pm (module definition) and *.pod (general documentation) files (using the File::Find module).


extract the complete documentation about a function from its source file using the PDL::Pod::Parser filter.



Quite a few shortcomings which will hopefully be fixed following discussions on the pdl-porters mailing list.


Copyright 1997 Christian Soeller <> and Karl Glazebrook <> All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is separated from the PDL distribution, the copyright notice should be included in the file.

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