NAME¶

pt::peg::export::container - PEG Export Plugin. Write CONTAINER format

SYNOPSIS¶

package require Tcl 8.5 9

package require pt::peg::export::container ?1?

package require pt::peg::to::container

export serial configuration

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 implements the parsing expression grammar export plugin for the generation of CONTAINER markup.

It resides in the Export section of the Core Layer of Parser Tools and is intended to be used by pt::peg::export, the export manager, sitting between it and the corresponding core conversion functionality provided by pt::peg::to::container.

IMAGE: arch_core_eplugins

While the direct use of this package with a regular interpreter is possible, this is strongly disrecommended and requires a number of contortions to provide the expected environment. The proper way to use this functionality depends on the situation:

[1]

In an untrusted environment the proper access is through the package pt::peg::export and the export manager objects it provides.

[2]

In a trusted environment however simply use the package pt::peg::to::container and access the core conversion functionality directly.

API¶

The API provided by this package satisfies the specification of the Plugin API found in the Parser Tools Export API specification.

export serial configuration

This command takes the canonical serialization of a parsing expression grammar, as specified in section PEG serialization format, and contained in serial, the configuration, a dictionary, and generates CONTAINER markup encoding the grammar. The created string is then returned as the result of the command.

CONFIGURATION¶

The CONTAINER export plugin recognizes the following configuration variables and changes its behaviour as they specify.

enum mode

The value of this configuration variable controls which methods of pt::peg instances the plugin will use to specify the grammar. There are two legal values

string template

If this configuration variable is set it is assumed to contain a string into which to put the generated code and other configuration data. The various locations are expected to be specified with the following placeholders:

If this configuration variable is not set, or empty, then the plugin falls back to a standard template, which is defined as "@code@".

Note that this plugin may ignore the standard configuration variables user, format, file, and their values, depending on the chosen template.

The content of the standard configuration variable name, if set, is used as name of the grammar in the output. Otherwise the plugin falls back to the default name a_pe_grammar.

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.

It has no direct formal specification beyond what was said above.

PEG calculator (Expression)


    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;


    Sign       <- '-' / '+'                                     ;


    Number     <- Sign? Digit+                                  ;


    Expression <- Term (AddOp Term)*                            ;


    MulOp      <- '*' / '/'                                     ;


    Term       <- Factor (MulOp Factor)*                        ;


    AddOp      <- '+'/'-'                                       ;


    Factor     <- '(' Expression ')' / Number                   ;
END;

snit::type a_pe_grammar {


    constructor {} {


        install myg using pt::peg::container ${selfns}::G


        $myg start {n Expression}


        $myg add   AddOp Digit Expression Factor MulOp Number Sign Term


        $myg modes {


            AddOp      value


            Digit      value


            Expression value


            Factor     value


            MulOp      value


            Number     value


            Sign       value


            Term       value


        }


        $myg rules {


            AddOp      {/ {t -} {t +}}


            Digit      {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}


            Expression {/ {x {t \50} {n Expression} {t \51}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}


            Factor     {x {n Term} {* {x {n AddOp} {n Term}}}}


            MulOp      {/ {t *} {t /}}


            Number     {x {? {n Sign}} {+ {n Digit}}}


            Sign       {/ {t -} {t +}}


            Term       {n Number}


        }


        return


    }


    component myg


    delegate method * to myg
}

PEG SERIALIZATION FORMAT¶

Here we specify the format used by the Parser Tools to serialize Parsing Expression Grammars as immutable values for transport, comparison, etc.

We distinguish between regular and canonical serializations. While a PEG may have more than one regular serialization only exactly one of them will be canonical.

regular serialization

canonical serialization

The canonical serialization of a grammar has the format as specified in the previous item, and then additionally satisfies the constraints below, which make it unique among all the possible serializations of this grammar.

PEG calculator (Expression)


    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;


    Sign       <- '-' / '+'                                     ;


    Number     <- Sign? Digit+                                  ;


    Expression <- Term (AddOp Term)*                            ;


    MulOp      <- '*' / '/'                                     ;


    Term       <- Factor (MulOp Factor)*                        ;


    AddOp      <- '+'/'-'                                       ;


    Factor     <- '(' Expression ')' / Number                   ;
END;

pt::grammar::peg {


    rules {


        AddOp      {is {/ {t -} {t +}}                                                                mode value}


        Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}


        Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}


        Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  mode value}


        MulOp      {is {/ {t *} {t /}}                                                                mode value}


        Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}


        Sign       {is {/ {t -} {t +}}                                                                mode value}


        Term       {is {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}


    }


    start {n Expression}
}

PE SERIALIZATION FORMAT¶

Here we specify the format used by the Parser Tools to serialize Parsing Expressions as immutable values for transport, comparison, etc.

We distinguish between regular and canonical serializations. While a parsing expression may have more than one regular serialization only exactly one of them will be canonical.

Regular serialization

Canonical serialization

The canonical serialization of a parsing expression has the format as specified in the previous item, and then additionally satisfies the constraints below, which make it unique among all the possible serializations of this parsing expression.

    Expression <- Term (AddOp Term)*

    {x {n Term} {* {x {n AddOp} {n Term}}}}

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¶

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

CATEGORY¶

Parsing and Grammars

COPYRIGHT¶

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