pt(n)                            Parser Tools                            pt(n)



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NAME
       pt - Parser Tools Application

SYNOPSIS
       package require Tcl  8.5

       pt generate resultformat ?options...? resultfile inputformat inputfile

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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 document describes pt, the main application of the module, a
       parser generator. Its intended audience are people who wish to create a
       parser for some language of theirs. Should you wish to modify the
       application instead, please see the section about the application's
       Internals for the basic references.

       It resides in the User Application Layer of Parser Tools.

       IMAGE: arch_user_app

COMMAND LINE
       pt generate resultformat ?options...? resultfile inputformat inputfile
              This sub-command of the application reads the parsing expression
              grammar stored in the inputfile in the format inputformat,
              converts it to the resultformat under the direction of the
              (format-specific) set of options specified by the user and
              stores the result in the resultfile.

              The inputfile has to exist, while the resultfile may be created,
              overwriting any pre-existing content of the file. Any missing
              directory in the path to the resultfile will be created as well.

              The exact form of the result for, and the set of options
              supported by the known result-formats, are explained in the
              upcoming sections of this document, with the list below
              providing an index mapping between format name and its
              associated section. In alphabetical order:


              c      A resultformat. See section C Parser.

              container
                     A resultformat. See section Grammar Container.

              critcl A resultformat. See section C Parser Embedded In Tcl.

              json   A input- and resultformat. See section JSON Grammar
                     Exchange.

              oo     A resultformat. See section TclOO Parser.

              peg    A input- and resultformat. See section PEG Specification
                     Language.

              snit   A resultformat. See section Snit Parser.

       Of the seven possible results four are parsers outright (c, critcl, oo,
       and snit), one (container) provides code which can be used in
       conjunction with a generic parser (also known as a grammar
       interpreter), and the last two (json and peg) are doing double-duty as
       input formats, allowing the transformation of grammars for exchange,
       reformatting, and the like.

       The created parsers fall into three categories:

       IMAGE: gen_options

       Specialized parsers implemented in C
              The fastest parsers are created when using the result formats c
              and critcl. The first returns the raw C code for the parser,
              while the latter wraps it into a Tcl package using CriTcl.

              This makes the latter much easier to use than the former. On the
              other hand, the former can be adapted to the users' requirements
              through a multitude of options, allowing for things like usage
              of the parser outside of a Tcl environment, something the critcl
              format doesn't support. As such the c format is meant for more
              advanced users, or users with special needs.

              A disadvantage of all the parsers in this section is the need to
              run them through a C compiler to make them actually executable.
              This is not something everyone has the necessary tools for. The
              parsers in the next section are for people under such
              restrictions.

       Specialized parsers implemented in Tcl
              As the parsers in this section are implemented in Tcl they are
              quite a bit slower than anything from the previous section. On
              the other hand this allows them to be used in pure-Tcl
              environments, or in environments which allow only a limited set
              of binary packages. In the latter case it will be advantageous
              to lobby for the inclusion of the C-based runtime support (notes
              below) into the environment to reduce the impact of Tcl's on the
              speed of these parsers.

              The relevant formats are snit and oo. Both place their result
              into a Tcl package containing a snit::type, or TclOO class
              respectively.

              Of the supporting runtime, which is the package pt::rde, the
              user has to know nothing but that it does exist and that the
              parsers are dependent on it. Knowledge of the API exported by
              the runtime for the parsers' consumption is not required by the
              parsers' users.

       Interpreted parsing implemented in Tcl
              The last category, grammar interpretation. This means that an
              interpreter for parsing expression grammars takes the
              description of the grammar to parse input for, and uses it guide
              the parsing process.  This is the slowest of the available
              options, as the interpreter has to continually run through the
              configured grammar, whereas the specialized parsers of the
              previous sections have the relevant knowledge about the grammar
              baked into them.

              The only places where using interpretation make sense is where
              the grammar for some input may be changed interactively by the
              user, as the interpretation allows for quick turnaround after
              each change, whereas the previous methods require the generation
              of a whole new parser, which is not as fast.  On the other hand,
              wherever the grammar to use is fixed, the previous methods are
              much more advantageous as the time to generate the parser is
              minuscule compared to the time the parser code is in use.

              The relevant result format is container.  It (quickly) generates
              grammar descriptions (instead of a full parser) which match the
              API expected by ParserTools' grammar interpreter.  The latter is
              provided by the package pt::peg::interp.

       All the parsers generated by critcl, snit, and oo, and the grammar
       interpreter share a common API for access to the actual parsing
       functionality, making them all plug-compatible.  It is described in the
       Parser API specification document.

PEG SPECIFICATION LANGUAGE
       peg, a language for the specification of parsing expression grammars is
       meant to be human readable, and writable as well, yet strict enough to
       allow its processing by machine. Like any computer language. It was
       defined to make writing the specification of a grammar easy, something
       the other formats found in the Parser Tools do not lend themselves too.

       For either an introduction to or the formal specification of the
       language, please go and read the PEG Language Tutorial.

       When used as a result-format this format supports the following
       options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -template string
              The value of this option is a string into which to put the
              generated text and the values of the other options. The various
              locations for user-data are expected to be specified with the
              placeholders listed below. The default value is "@code@".

              @user@ To be replaced with the value of the option -user.

              @format@
                     To be replaced with the the constant PEG.

              @file@ To be replaced with the value of the option -file.

              @name@ To be replaced with the value of the option -name.

              @code@ To be replaced with the generated text.

JSON GRAMMAR EXCHANGE
       The json format for parsing expression grammars was written as a data
       exchange format not bound to Tcl. It was defined to allow the exchange
       of grammars with PackRat/PEG based parser generators for other
       languages.

       For the formal specification of the JSON grammar exchange format,
       please go and read The JSON Grammar Exchange Format.

       When used as a result-format this format supports the following
       options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -indented boolean
              If this option is set the system will break the generated JSON
              across lines and indent it according to its inner structure,
              with each key of a dictionary on a separate line.

              If the option is not set (the default), the whole JSON object
              will be written on a single line, with minimum spacing between
              all elements.

       -aligned boolean
              If this option is set the system will ensure that the values for
              the keys in a dictionary are vertically aligned with each other,
              for a nice table effect.  To make this work this also implies
              that -indented is set.

              If the option is not set (the default), the output is formatted
              as per the value of indented, without trying to align the values
              for dictionary keys.

C PARSER EMBEDDED IN TCL
       The critcl format is executable code, a parser for the grammar. It is a
       Tcl package with the actual parser implementation written in C and
       embedded in Tcl via the critcl package.

       This result-format supports the following options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -class string
              The value of this option is the name of the class to generate,
              without leading colons.  The default value is CLASS.

              For a simple value X without colons, like CLASS, the parser
              command will be X::X. Whereas for a namespaced value X::Y the
              parser command will be X::Y.

       -package string
              The value of this option is the name of the package to generate.
              The default value is PACKAGE.

C PARSER
       The c format is executable code, a parser for the grammar. The parser
       implementation is written in C and can be tweaked to the users' needs
       through a multitude of options.

       The critcl format, for example, is implemented as a canned
       configuration of these options on top of the generator for c.

       This result-format supports the following options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -template string
              The value of this option is a string into which to put the
              generated text and the other configuration settings. The various
              locations for user-data are expected to be specified with the
              placeholders listed below. The default value is "@code@".

              @user@ To be replaced with the value of the option -user.

              @format@
                     To be replaced with the the constant C/PARAM.

              @file@ To be replaced with the value of the option -file.

              @name@ To be replaced with the value of the option -name.

              @code@ To be replaced with the generated Tcl code.
       The following options are special, in that they will occur within the
       generated code, and are replaced there as well.

              @statedecl@
                     To be replaced with the value of the option state-decl.

              @stateref@
                     To be replaced with the value of the option state-ref.

              @strings@
                     To be replaced with the value of the option string-
                     varname.

              @self@ To be replaced with the value of the option self-command.

              @def@  To be replaced with the value of the option fun-
                     qualifier.

              @ns@   To be replaced with the value of the option namespace.

              @main@ To be replaced with the value of the option main.

              @prelude@
                     To be replaced with the value of the option prelude.

       -state-decl string
              A C string representing the argument declaration to use in the
              generated parsing functions to refer to the parsing state. In
              essence type and argument name.  The default value is the string
              RDE_PARAM p.

       -state-ref string
              A C string representing the argument named used in the generated
              parsing functions to refer to the parsing state.  The default
              value is the string p.

       -self-command string
              A C string representing the reference needed to call the
              generated parser function (methods ...) from another parser
              fonction, per the chosen framework (template).  The default
              value is the empty string.

       -fun-qualifier string
              A C string containing the attributes to give to the generated
              functions (methods ...), per the chosen framework (template).
              The default value is static.

       -namespace string
              The name of the C namespace the parser functions (methods, ...)
              shall reside in, or a general prefix to add to the function
              names.  The default value is the empty string.

       -main string
              The name of the main function (method, ...) to be called by the
              chosen framework (template) to start parsing input.  The default
              value is __main.

       -string-varname string
              The name of the variable used for the table of strings used by
              the generated parser, i.e. error messages, symbol names, etc.
              The default value is p_string.

       -prelude string
              A snippet of code to be inserted at the head of each generated
              parsing function.  The default value is the empty string.

       -indent integer
              The number of characters to indent each line of the generated
              code by.  The default value is 0.

SNIT PARSER
       The snit format is executable code, a parser for the grammar. It is a
       Tcl package holding a snit::type, i.e. a class, whose instances are
       parsers for the input grammar.

       This result-format supports the following options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -class string
              The value of this option is the name of the class to generate,
              without leading colons. Note, it serves double-duty as the name
              of the package to generate too.  The default value is CLASS.

TCLOO PARSER
       The oo format is executable code, a parser for the grammar. It is a Tcl
       package holding a TclOO class, whose instances are parsers for the
       input grammar.

       This result-format supports the following options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -class string
              The value of this option is the name of the class to generate,
              without leading colons. Note, it serves double-duty as the name
              of the package to generate too.  The default value is CLASS.

GRAMMAR CONTAINER
       The container format is another form of describing parsing expression
       grammars. While data in this format is executable it does not
       constitute a parser for the grammar. It always has to be used in
       conjunction with the package pt::peg::interp, a grammar interpreter.

       The format represents grammars by a snit::type, i.e. class, whose
       instances are API-compatible to the instances of the pt::peg::container
       package, and which are preloaded with the grammar in question.

       This result-format supports the following options:

       -file string
              The value of this option is the name of the file or other entity
              from which the grammar came, for which the command is run. The
              default value is unknown.

       -name string
              The value of this option is the name of the grammar we are
              processing.  The default value is a_pe_grammar.

       -user string
              The value of this option is the name of the user for which the
              command is run. The default value is unknown.

       -mode bulk|incremental
              The value of this option controls which methods of
              pt::peg::container instances are used to specify the grammar,
              i.e. preload it into the container. There are two legal values,
              as listed below. The default is bulk.

              bulk   In this mode the methods start, add, modes, and rules are
                     used to specify the grammar in a bulk manner, i.e. as a
                     set of nonterminal symbols, and two dictionaries mapping
                     from the symbols to their semantic modes and parsing
                     expressions.

                     This mode is the default.

              incremental
                     In this mode the methods start, add, mode, and rule are
                     used to specify the grammar piecemal, with each
                     nonterminal having its own block of defining commands.

       -template string
              The value of this option is a string into which to put the
              generated code and the other configuration settings. The various
              locations for user-data are expected to be specified with the
              placeholders listed below. The default value is "@code@".

              @user@ To be replaced with the value of the option -user.

              @format@
                     To be replaced with the the constant CONTAINER.

              @file@ To be replaced with the value of the option -file.

              @name@ To be replaced with the value of the option -name.

              @mode@ To be replaced with the value of the option -mode.

              @code@ To be replaced with the generated code.

EXAMPLE
       In this section we are working a complete example, starting with a PEG
       grammar and ending with running the parser generated from it over some
       input, following the outline shown in the figure below:

       IMAGE: flow

       Our grammar, assumed to the stored in the file "calculator.peg" is

              PEG calculator (Expression)
                  Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9';
                  Sign       <- '-' / '+';
                  Number     <- Sign? Digit+;
                  Expression <- '(' Expression ')' / (Factor (MulOp Factor)*);
                  MulOp      <- '*' / '/';
                  Factor     <- Term (AddOp Term)*;
                  AddOp      <- '+'/'-';
                  Term       <- Number;
              END;

       From this we create a snit-based parser via

              pt generate  snit calculator.tcl  -class calculator  -name  calculator  peg calculator.peg

       which leaves us with the parser package and class written to the file
       "calculator.tcl".  Assuming that this package is then properly
       installed in a place where Tcl can find it we can now use this class
       via a script like

                  package require calculator

                  lassign $argv input
                  set channel [open $input r]

                  set parser [calculator]
                  set ast [$parser parse $channel]
                  $parser destroy
                  close $channel

                  ... now process the returned abstract syntax tree ...

       where the abstract syntax tree stored in the variable will look like

              set ast {Expression 0 4
                  {Factor 0 4
                      {Term 0 2
                          {Number 0 2
                              {Digit 0 0}
                              {Digit 1 1}
                              {Digit 2 2}
                          }
                      }
                      {AddOp 3 3}
                      {Term 4 4
                          {Number 4 4
                              {Digit 4 4}
                          }
                      }
                  }
              }


       assuming that the input file and channel contained the text
               120+5
       A more graphical representation of the tree would be

       IMAGE: expr_ast

       Regardless, at this point it is the user's responsibility to work with
       the tree to reach whatever goal she desires. I.e. analyze it, transform
       it, etc. The package pt::ast should be of help here, providing commands
       to walk such ASTs structures in various ways.

       One important thing to note is that the parsers used here return a data
       structure representing the structure of the input per the grammar
       underlying the parser. There are no callbacks during the parsing
       process, i.e. no parsing actions, as most other parsers will have.

       Going back to the last snippet of code, the execution of the parser for
       some input, note how the parser instance follows the specified Parser
       API.

INTERNALS
       This section is intended for users of the application which wish to
       modify or extend it. Users only interested in the generation of parsers
       can ignore it.

       The main functionality of the application is encapsulated in the
       package pt::pgen. Please read it for more information.

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 SF Trackers [http://sourceforge.net/tracker/?group_id=12883].
       Please also report any ideas for enhancements you may have for either
       package and/or documentation.

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>




pt                                     1                                 pt(n)
