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# doctools::tcl::parse(n) 1 tcllib "Documentation tools"

## Name

doctools::tcl::parse - Processing text in 'subst -novariables' format

## Synopsis

- package require Tcl 8.4
- package require snit
- package require fileutil
- package require logger
- package require struct::list
- package require struct::stack
- package require struct::set
- package require treeql
- package require doctools::tcl::parse

- ::doctools::tcl::parse text tree text ?root?
- ::doctools::tcl::parse file tree path ?root?

## Description

This package provides commands for parsing text with embedded Tcl commands as accepted by the Tcl builtin command subst -novariables. The result of the parsing is an abstract syntax tree.

This is an internal package of doctools, for use by the higher level parsers processing the docidx, doctoc, and doctools markup languages.

## API

::doctools::tcl::parse text tree text ?root?

  The command takes the text and parses it under the assumption that it contains a string acceptable to the Tcl builtin command subst -novariables. Errors are thrown otherwise during the parsing. The format used for these errors in described in section Error format.

  The command returns the empty string as it result. The actual result of the parsing is entered into the tree structure tree, under the node root. If root is not specified the root of tree is used. The tree has to exist and be the command of a tree object which supports the same methods as trees created by the package struct::tree.

  In case of errors tree will be left in an undefined state.

::doctools::tcl::parse file tree path ?root?

  The same as text, except that the text to parse is read from the file specified by path.

## Error format

When the parser encounters a problem in the input it will throw an error using the format described here.

1. The message will contain the reason for the problem (unexpected character or end of input in input), the character in question, if any, and the line and column the problem was found at, in a human readable form. This part is not documented further as its format may change as we see fit. It is intended for human consumption, not machine.

2. The error code however will contain a machine-readable representation of the problem, in the form of a 5-element list containing, in the order listed below

   1. the constant string doctools::tcl::parse

   2. the cause of the problem, one of

      char

        Unexpected character in input

      eof

        Unexpected end of the input

   3. The location of the problem as offset from the beginning of the input, counted in characters. Note: Line markers count as one character.

   4. The line the problem was found on (counted from 1 (one)),

   5. The column the problem was found at (counted from 0 (zero))

## Tree Structure

After successfully parsing a string the generated tree will have the following structure:

1. In the following items the word 'root' refers to the node which was specified as the root of the tree when invoking either text or file. This may be the actual root of the tree.

2. All the following items further ignore the possibility of pre-existing attributes in the pre-existing nodes. If attributes exists with the same names as the attributes used by the parser the pre-existing values are written over. Attributes with names not clashing with the parser's attributes are not touched.

3. The root node has no attributes.

4. All other nodes have the attributes

   type

     The value is a string from the set { Command , Text , Word }

   range

     The value is either empty or a 2-element list containing integer numbers. The numbers are the offsets of the first and last character in the input text, of the token described by the node,.

   line

     The value is an integer, it describes the line in the input the token described by the node ends on. Lines are counted from 1 (one).

   col

     The value is an integer, it describes the column in the line in the input the token described by the node ends on. Columns are counted from 0 (zero).

5. The children of the root, if any, are of type Command and Text, in semi-alternation. This means: After a Text node a Command node has to follow, and anything can follow a Command node, a Text or other Command node.

6. The children of a Command node, if any, are of type Command, and Text, and Word, they describe the arguments of the command.

7. The children of a Word node, if any, are of type Command, Text, in semi-alternation. This means: After a Text node a Command node has to follow, and anything can follow a Command node, a Text or other Command node.

8. A Word node without children represents the empty string.

9. All Text nodes are leaves of the tree.

10. All leaves of the tree are either Text or Command nodes. Word nodes cannot be leaves.

## Bugs, Ideas, Feedback

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

## Keywords

Tcl syntax, command, doctools, parser, subst, word

## Category

Documentation tools

## Copyright

Copyright © 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>