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EuroTcl/OpenACS 11 - 12 JULY 2024, VIENNA


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NAME

pt_export_api - Parser Tools Export API

Table Of Contents

SYNOPSIS

package require Tcl 8.5 9

CONVERTER reset
CONVERTER configure
CONVERTER configure option
CONVERTER configure option value...
CONVERTER convert serial
::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 document describes two APIs. First the API shared by all packages for the conversion of Parsing Expression Grammars into some other format, and then the API shared by the packages which implement the export plugins sitting on top of the conversion packages.

Its intended audience are people who wish to create their own converter for some type of output, and/or an export plugin for their or some other converter.

It resides in the Export section of the Core Layer of Parser Tools.

Converter API

Any (grammar) export converter has to follow the rules set out below:

  1. A converter is a package. Its name is arbitrary, however it is recommended to put it under the ::pt::peg::to namespace.

  2. The package provides either a single Tcl command following the API outlined below, or a class command whose instances follow the same API. The commands which follow the API are called converter commands.

  3. A converter command has to provide the following three methods with the given signatures and semantics. Converter commands are allowed to provide more methods of their own, but not less, and they may not provide different semantics for the standardized methods.

    • CONVERTER reset

      This method has to reset the configuration of the converter to its default settings. The result of the method has to be the empty string.

    • CONVERTER configure

      This method, in this form, has to return a dictionary containing the current configuration of the converter.

    • CONVERTER configure option

      This method, in this form, has to return the current value of the specified configuration option of the converter.

      Please read the section Options for the set of standard options any converter has to accept. Any other options accepted by a specific converter will be described in its manpage.

    • CONVERTER configure option value...

      This command, in this form, sets the specified options of the converter to the given values.

      Please read the section Options for the set of standard options a converter has to accept. Any other options accepted by a specific converter will be described in its manpage.

    • CONVERTER convert serial

      This method has to accept the canonical serialization of a parsing expression grammar, as specified in section PEG serialization format, and contained in serial. The result of the method has to be the result of converting the input grammar into whatever the converter is for, per its configuration.

Plugin API

Any (grammar) export plugin has to follow the rules set out below:

  1. A plugin is a package.

  2. The name of a plugin package has the form pt::peg::export::FOO, where FOO is the name of the format the plugin will generate output for.

  3. The plugin can expect that the package pt::peg::export::plugin is present, as indicator that it was invoked from a genuine plugin manager.

    It is recommended that a plugin does check for the presence of this package.

  4. A plugin has to provide a single command, in the global namespace, with the signature shown below. Plugins are allowed to provide more command of their own, but not less, and they may not provide different semantics for the standardized command.

    • ::export serial configuration

      This command has to accept the canonical serialization of a parsing expression grammar and the configuration for the converter invoked by the plugin. The result of the command has to be the result of the converter invoked by the plugin for th input grammar and configuration.

      • string serial

        This argument will contain the canonical serialization of the parsing expression grammar for which to generate the output. The specification of what a canonical serialization is can be found in the section PEG serialization format.

      • dictionary configuration

        This argument will contain the configuration to configure the converter with before invoking it, as a dictionary mapping from options to values.

        Please read the section Options for the set of standard options any converter has to accept, and thus any plugin as well. Any other options accepted by a specific plugin will be described in its manpage.

  5. A single usage cycle of a plugin consists of an invokation of the command export. This call has to leave the plugin in a state where another usage cycle can be run without problems.

Options

Each export converter and plugin for an export converter has to accept the options below in their configure method. Converters are allowed to ignore the contents of these options when performing a conversion, but they must not reject them. Plugins are expected to pass the options given to them to the converter they are invoking.

Usage

To use a converter do

# Get the converter (single command here, not class)
package require the-converter-package

# Provide a configuration
theconverter configure ...

# Perform the conversion
set result [theconverter convert $thegrammarserial]

... process the result ...

To use a plugin FOO do

# Get an export plugin manager
package require pt::peg::export
pt::peg::export E

# Provide a configuration
E configuration set ...

# Run the plugin, and the converter inside.
set result [E export serial $grammarserial FOO]

... process the result ...

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.

Example

Assuming the following PEG for simple mathematical expressions

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;

then its canonical serialization (except for whitespace) is

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.

Example

Assuming the parsing expression shown on the right-hand side of the rule

Expression <- Term (AddOp Term)*

then its canonical serialization (except for whitespace) is

{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. 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 © 2009 Andreas Kupries