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# page(n) 1.0 tcllib "Development Tools"

## Name

page - Parser Generator

## Synopsis

- page ?options...? ?input ?output??

## Description

The application described by this document, page, is actually not just a parser generator, as the name implies, but a generic tool for the execution of arbitrary transformations on texts.

Its genericity comes through the use of plugins for reading, transforming, and writing data, and the predefined set of plugins provided by Tcllib is for the generation of memoizing recursive descent parsers (aka packrat parsers) from grammar specifications (Parsing Expression Grammars).

page is written on top of the package page::pluginmgr, wrapping its functionality into a command line based application. All the other page::* packages are plugin and/or supporting packages for the generation of parsers. The parsers themselves are based on the packages grammar::peg, grammar::peg::interp, and grammar::mengine.

### COMMAND LINE

page ?options...? ?input ?output??

  This is general form for calling page. The application will read the contents of the file input, process them under the control of the specified options, and then write the result to the file output.

  If input is the string - the data to process will be read from stdin instead of a file. Analogously the result will be written to stdout instead of a file if output is the string -. A missing output or input specification causes the application to assume -.

  The detailed specifications of the recognized options are provided in section OPTIONS.

  path input (in)

    This argument specifies the path to the file to be processed by the application, or -. The last value causes the application to read the text from stdin. Otherwise it has to exist, and be readable. If the argument is missing - is assumed.

  path output (in)

    This argument specifies where to write the generated text. It can be the path to a file, or -. The last value causes the application to write the generated documented to stdout.

    If the file output does not exist then [file dirname $output] has to exist and must be a writable directory, as the application will create the fileto write to.

    If the argument is missing - is assumed.

### OPERATION

... reading ... transforming ... writing - plugins - pipeline ...

### OPTIONS

This section describes all the options available to the user of the application. Options are always processed in order. I.e. of both --help and --version are specified the option encountered first has precedence.

Unknown options specified before any of the options -rd, -wr, or -tr will cause processing to abort with an error. Unknown options coming in between these options, or after the last of them are assumed to always take a single argument and are associated with the last plugin option coming before them. They will be checked after all the relevant plugins, and thus the options they understand, are known. I.e. such unknown options cause error if and only if the plugin option they are associated with does not understand them, and was not superceded by a plugin option coming after.

Default options are used if and only if the command line did not contain any options at all. They will set the application up as a PEG-based parser generator. The exact list of options is

    -c peg

And now the recognized options and their arguments, if they have any:

--help
-h
-?

  When one of these options is found on the command line all arguments coming before or after are ignored. The application will print a short description of the recognized options and exit.

--version
-V

  When one of these options is found on the command line all arguments coming before or after are ignored. The application will print its own revision and exit.

-P

  This option signals the application to activate visual feedback while reading the input.

-T

  This option signals the application to collect statistics while reading the input and to print them after reading has completed, before processing started.

-D

  This option signals the application to activate logging in the Safe base, for the debugging of problems with plugins.

-r parser
-rd parser
--reader parser

  These options specify the plugin the application has to use for reading the input. If the options are used multiple times the last one will be used.

-w generator
-wr generator
--writer generator

  These options specify the plugin the application has to use for generating and writing the final output. If the options are used multiple times the last one will be used.

-t process
-tr process
--transform process

  These options specify a plugin to run on the input. In contrast to readers and writers each use will not supersede previous uses, but add each chosen plugin to a list of transformations, either at the front, or the end, per the last seen use of either option -p or -a. The initial default is to append the new transformations.

-a
--append

  These options signal the application that all following transformations should be added at the end of the list of transformations.

-p
--prepend

  These options signal the application that all following transformations should be added at the beginning of the list of transformations.

--reset

  This option signals the application to clear the list of transformations. This is necessary to wipe out the default transformations used.

-c file
--configuration file

  This option causes the application to load a configuration file and/or plugin. This is a plugin which in essence provides a pre-defined set of commandline options. They are processed exactly as if they have been specified in place of the option and its arguments. This means that unknown options found at the beginning of the configuration file are associated with the last plugin, even if that plugin was specified before the configuration file itself. Conversely, unknown options coming after the configuration file can be associated with a plugin specified in the file.

  If the argument is a file which cannot be loaded as a plugin the application will assume that its contents are a list of options and their arguments, separated by space, tabs, and newlines. Options and argumentes containing spaces can be quoted via double-quotes (") and quotes ('). The quote character can be specified within in a quoted string by doubling it. Newlines in a quoted string are accepted as is.

### PLUGINS

page makes use of four different types of plugins, namely: readers, writers, transformations, and configurations. Here we provide only a basic introduction on how to use them from page. The exact APIs provided to and expected from the plugins can be found in the documentation for page::pluginmgr, for those who wish to write their own plugins.

Plugins are specified as arguments to the options -r, -w, -t, -c, and their equivalent longer forms. See the section OPTIONS for reference.

Each such argument will be first treated as the name of a file and this file is loaded as the plugin. If however there is no file with that name, then it will be translated into the name of a package, and this package is then loaded. For each type of plugins the package management searches not only the regular paths, but a set application- and type-specific paths as well. Please see the section PLUGIN LOCATIONS for a listing of all paths and their sources.

-c name

  Configurations. The name of the package for the plugin name is "page::config::name".

  We have one predefined plugin:

  peg

    It sets the application up as a parser generator accepting parsing expression grammars and writing a packrat parser in Tcl. The actual arguments it specifies are:

        	--reset
        	--append
        	--reader    peg
        	--transform reach
        	--transform use
        	--writer    me

-r name

  Readers. The name of the package for the plugin name is "page::reader::name".

  We have five predefined plugins:

  peg

    Interprets the input as a parsing expression grammar (PEG) and generates a tree representation for it. Both the syntax of PEGs and the structure of the tree representation are explained in their own manpages.

  hb

    Interprets the input as Tcl code as generated by the writer plugin hb and generates its tree representation.

  ser

    Interprets the input as the serialization of a PEG, as generated by the writer plugin ser, using the package grammar::peg.

  lemon

    Interprets the input as a grammar specification as understood by Richard Hipp's LEMON parser generator and generates a tree representation for it. Both the input syntax and the structure of the tree representation are explained in their own manpages.

  treeser

    Interprets the input as the serialization of a struct::tree. It is validated as such, but nothing else. It is not assumed to be the tree representation of a grammar.

-w name

  Writers. The name of the package for the plugin name is "page::writer::name".

  We have eight predefined plugins:

  identity

    Simply writes the incoming data as it is, without making any changes. This is good for inspecting the raw result of a reader or transformation.

  null

    Generates nothing, and ignores the incoming data structure.

  tree

    Assumes that the incoming data structure is a struct::tree and generates an indented textual representation of all nodes, their parental relationships, and their attribute information.

  peg

    Assumes that the incoming data structure is a tree representation of a PEG or other other grammar and writes it out as a PEG. The result is nicely formatted and partially simplified (strings as sequences of characters). A pretty printer in essence, but can also be used to obtain a canonical representation of the input grammar.

  tpc

    Assumes that the incoming data structure is a tree representation of a PEG or other other grammar and writes out Tcl code defining a package which defines a grammar::peg object containing the grammar when it is loaded into an interpreter.

  hb

    This is like the writer plugin tpc, but it writes only the statements which define stat expression and grammar rules. The code making the result a package is left out.

  ser

    Assumes that the incoming data structure is a tree representation of a PEG or other other grammar, transforms it internally into a grammar::peg object and writes out its serialization.

  me

    Assumes that the incoming data structure is a tree representation of a PEG or other other grammar and writes out Tcl code defining a package which implements a memoizing recursive descent parser based on the match engine (ME) provided by the package grammar::mengine.

-t name

  Transformers. The name of the package for the plugin name is "page::transform::name".

  We have two predefined plugins:

  reach

    Assumes that the incoming data structure is a tree representation of a PEG or other other grammar. It determines which nonterminal symbols and rules are reachable from start-symbol/expression. All nonterminal symbols which were not reached are removed.

  use

    Assumes that the incoming data structure is a tree representation of a PEG or other other grammar. It determines which nonterminal symbols and rules are able to generate a finite sequences of terminal symbols (in the sense for a Context Free Grammar). All nonterminal symbols which were not deemed useful in this sense are removed.

### PLUGIN LOCATIONS

The application-specific paths searched by page either are, or come from:

1. The directory "~/.page/plugin"

2. The environment variable PAGE_PLUGINS

3. The registry entry HKEY_LOCAL_MACHINE\SOFTWARE\PAGE\PLUGINS

4. The registry entry HKEY_CURRENT_USER\SOFTWARE\PAGE\PLUGINS

The type-specific paths searched by page either are, or come from:

1. The directory "~/.page/plugin/<TYPE>"

2. The environment variable PAGE_<TYPE>_PLUGINS

3. The registry entry HKEY_LOCAL_MACHINE\SOFTWARE\PAGE\<TYPE>\PLUGINS

4. The registry entry HKEY_CURRENT_USER\SOFTWARE\PAGE\<TYPE>\PLUGINS

Where the placeholder <TYPE> is always one of the values below, properly capitalized.

1. reader

2. writer

3. transform

4. config

The registry entries are specific to the Windows(tm) platform, all other platforms will ignore them.

The contents of both environment variables and registry entries are interpreted as a list of paths, with the elements separated by either colon (Unix), or semicolon (Windows).

## Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category page of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

## See Also

page::pluginmgr

## Keywords

parser generator, text processing

## Category

Page Parser Generator

## Copyright

Copyright © 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>