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# page_util_peg(n) 1.0 tcllib "Parser generator tools"

## Name

page_util_peg - page PEG transformation utilities

## Synopsis

- package require page::util::peg ?0.1?
- package require snit

- ::page::util::peg::symbolNodeOf tree node
- ::page::util::peg::symbolOf tree node
- ::page::util::peg::updateUndefinedDueRemoval tree
- ::page::util::peg::flatten treequery tree
- ::page::util::peg::getWarnings tree
- ::page::util::peg::printWarnings msg
- ::page::util::peg::peOf tree eroot
- ::page::util::peg::printTclExpr pe

## Description

This package provides a few common operations to PEG transformations. They assume a Normalized PE Grammar Tree as input, see the package page::util::norm::peg, possibly augmented with attributes coming from transformations not in conflict with the base definition.

## API

::page::util::peg::symbolNodeOf tree node

  Given an arbitrary expression node in the AST tree it determines the node (itself or an ancestor) containing the name of the nonterminal symbol the node belongs to, and returns its id. The result is either the root of the tree (for the start expression), or a definition node.

::page::util::peg::symbolOf tree node

  As ::page::util::peg::symbolNodeOf, but returns the symbol name instead of the node.

::page::util::peg::updateUndefinedDueRemoval tree

  The removal of nodes in the AST tree can cause symbols to lose one or more users.

      	A used by B and C,
      	B is reachable,
      	C is not,
      	so A now loses the node in the expression for C calling it,
      	or rather, not calling it anymore.

  This command updates the cross-references and which nonterminals are now undefined.

::page::util::peg::flatten treequery tree

  This commands flattens nested sequence and choice operators in the AST tree, re-using the treeql object treequery to run the query determining which nodes to cut.

::page::util::peg::getWarnings tree

  This command looks at the attributes of the AST tree for problems with the grammar and issues warnings. They do not prevent us from writing the grammar, but still represent problems with it the user should be made aware of.

  The result of the command is a dictionary mapping nonterminal names to their associated warnings.

::page::util::peg::printWarnings msg

  The argument of the command is a dictionary mapping nonterminal names to their associated warnings, as generated by, for example, the command ::page::util::peg::getWarnings.

  The warnings contained therein are formatted and then printed via the log command page_info. This means that this command can be used only from within a plugin managed by the package page::pluginmgr.

::page::util::peg::peOf tree eroot

  This command converts the parsing expression starting at the node eroot in the AST tree into a nested list. The exact syntax of this list specified by the package grammar::peg.

::page::util::peg::printTclExpr pe

  This command converts the parsing expression contained in the nested list pe into a Tcl string which can be placed into a Tcl script. See the package grammar::peg for the exact syntax of pe.

## 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.

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

PEG, page, parser generator, parsing expression grammar, text processing, transformation

## Category

Page Parser Generator

## Copyright

Copyright © 2007 Andreas Kupries <andreas_kupries@users.sourceforge.net>