# page_util_flow(3tcl) 1.0 page "Parser generator tools"

## Name

page_util_flow - page dataflow/treewalker utility

## Synopsis

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

- ::page::util::flow start flowvar nodevar script
- flow visit node
- flow visitl nodelist
- flow visita node...

## Description

This package provides a single utility command for easy dataflow based manipulation of arbitrary data structures, especially abstract syntax trees.

## API

::page::util::flow start flowvar nodevar script

  This command contains the core logic to drive the walking of an arbitrary data structure which can partitioned into separate parts. Examples of such structures are trees and graphs.

  The command makes no assumptions at all about the API of the structure to be walked, except that that its parts, here called nodes, are identified by strings. These strings are taken as is, from the arguments, and the body, and handed back to the body, without modification.

  Access to the actual data structure, and all decisions regarding which nodes to visit in what order are delegated to the body of the loop, i.e. the script.

  The body is invoked first for the nodes in the start-set specified via start), and from then on for the nodes the body has requested to be visited. The command stops when the set of nodes to visit becomes empty. Note that a node can be visited more than once. The body has complete control about this.

  The body is invoked in the context of the caller. The variable named by nodevar will be set to the current node, and the variable named by flowvar will be set to the command of the flow object through which the body can request the nodes to visit next. The API provided by this object is described in the next section, FLOW API.

  Note that the command makes no promises regarding the order in which nodes are visited, excpt that the nodes requested to be visited by the current iteration will be visited afterward, in some order.

## FLOW API

This section describes the API provided by the flow object made accessible to the body script of ::page::util::flow.

flow visit node

  Invoking this method requests that the node n is visited after the current iteration.

flow visitl nodelist

  Invoking this method requests that all the nodes found in the list nodelist are visited after the current iteration.

flow visita node...

  This is the variadic arguments form of the method visitl, see above.

## 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

dataflow, graph walking, page, parser generator, text processing, tree walking

## Category

Page Parser Generator

## Copyright

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