---
name: "page_util_peg"
section: "3tcl"
platform: "linux"
package: "tcllib"
version: "2.0+dfsg-4"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/page_util_peg"
---

# page\_util\_peg(3tcl)

page PEG transformation utilities

```

```

## NAME

page\_util\_peg - page PEG transformation utilities

## SYNOPSIS

package require **page::util::peg ?0.2?**

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* \[http://core.tcl.tk/tcllib/reportlist\]. 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

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

## CATEGORY

Page Parser Generator

## COPYRIGHT

```
Copyright (c) 2007 Andreas Kupries <andreas_kupries@users.sourceforge.net>
```