NAME

       pt_parse_peg - Parser Tools PEG Parser

SYNOPSIS

       package require Tcl  8.5

       package require pt::parse::peg  1

       pt::parse::peg ?objectName?

       objectName destroy

       objectName parse chan

       objectName parset text

________________________________________________________________________________________________________________

DESCRIPTION

       Are  you lost ?  Do you have trouble understanding this document ?  In that case please read the overview
       provided by the Introduction to Parser Tools. This document is the entrypoint to  the  whole  system  the
       current package is a part of.

       This  package  provides  a  class  whose instances are parsers for parsing expression grammars in textual
       form.

CLASS API

       pt::parse::peg ?objectName?
              The class command constructs parser instances, i.e. objects. The result  of  the  command  is  the
              fully-qualified name of the instance command.

              If no objectName is specified the class will generate and use an automatic name. If the objectName
              was specified, but is not fully qualified the command will be created in the current namespace.

INSTANCES API

       All parser instances provide at least the methods shown below:

       objectName destroy
              This  method  destroys  the parser instance, releasing all claimed memory and other resources, and
              deleting the instance command.

              The result of the command is the empty string.

       objectName parse chan
              This method runs the parser using the contents of chan as input (starting at the current  location
              in  the  channel), until parsing is not possible anymore, either because parsing has completed, or
              run into a syntax error.

              Note here that the Parser Tools are based on Tcl 8.5+. In other words, the channel argument is not
              restricted to files, sockets, etc. We have the full power of reflected channels available.

              It should also be noted that the parser pulls the characters from the input  stream  as  it  needs
              them.  If a parser created by this package has to be operated in a push aka event-driven manner it
              will be necessary to go to Tcl 8.6+ and use the coroutine::auto to wrap it into a coroutine  where
              read is properly changed for push-operation.

              Upon successful completion the command returns an abstract syntax tree as its result.  This AST is
              in the form specified in section AST serialization format.  As a plain nested Tcl-list it can then
              be  processed  with  any Tcl commands the user likes, doing transformations, semantic checks, etc.
              To help in this the package pt::ast provides a set of convenience commands for validation  of  the
              tree's  basic  structure,  printing it for debugging, and walking it either from the bottom up, or
              top down.

              When encountering a syntax error the command will throw an error instead.  This error  will  be  a
              4-element Tcl-list, containing, in the order listed below:

              [1]    The string pt::rde identifying it as parser runtime error.

              [2]    The  location  of  the  parse  error,  as character offset from the beginning of the parsed
                     input.

              [3]    The location of parse error, now as a 2-element list containing line-number and  column  in
                     the line.

              [4]    A  set  of atomic parsing expressions indicating encoding the characters and/or nonterminal
                     symbols the parser expected to see at the location of the parse error,  but  did  not  get.
                     For the specification of atomic parsing expressions please see the section PE serialization
                     format.

       objectName parset text
              This  method runs the parser using the string in text as input.  In all other ways it behaves like
              the method parse, shown above.

BUGS, IDEAS, FEEDBACK

       This document, and the package it describes, will undoubtedly contain bugs and  other  problems.   Please
       report  such  in  the  category pt of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist].  Please
       also report any ideas for enhancements you may have for either package and/or documentation.

       When proposing code changes, please provide unified diffs, i.e the output of diff -u.

       Note further that attachments are strongly preferred over inlined patches. Attachments  can  be  made  by
       going  to the Edit form of the ticket immediately after its creation, and then using the left-most button
       in the secondary navigation bar.

KEYWORDS

       EBNF,  LL(k),  PEG,  TDPL,  context-free  languages,  expression,  grammar,  matching,  parser,   parsing
       expression,  parsing  expression grammar, push down automaton, recursive descent, state, top-down parsing
       languages, transducer

CATEGORY

       Parsing and Grammars

COPYRIGHT

       Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>

tcllib                                                  1                                     pt_parse_peg(3tcl)