Provided by: tcllib_1.19-dfsg-2_all 
NAME
grammar::fa::dexec - Execute deterministic finite automatons
SYNOPSIS
package require Tcl 8.4
package require snit
package require grammar::fa::dexec ?0.2?
::grammar::fa::dexec daName fa ?-any any? ?-command cmdprefix?
daName option ?arg arg ...?
daName destroy
daName put symbol
daName reset
daName state
cmdprefix error code message
cmdprefix final stateid
cmdprefix reset
cmdprefix state stateid
________________________________________________________________________________________________________________
DESCRIPTION
This package provides a class for executors constructed from deterministic finite automatons (DFA).
Executors are objects which are given a string of symbols in a piecemal fashion, perform state
transitions and report back when they enter a final state, or find an error in the input. For the actual
creation of the DFAs the executors are based on we have the packages grammar::fa and grammar::fa::op.
The objects follow a push model. Symbols are pushed into the executor, and when something important
happens, i.e. error occurs, a state transition, or a final state is entered this will be reported via the
callback specified via the option -command. Note that conversion of this into a pull model where the
environment retrieves messages from the object and the object uses a callback to ask for more symbols is
a trivial thing.
Side note: The acceptor objects provided by grammar::fa::dacceptor could have been implemented on top of
the executors provided here, but were not, to get a bit more performance (we avoid a number of method
calls and the time required for their dispatch).
API
The package exports the API described here.
::grammar::fa::dexec daName fa ?-any any? ?-command cmdprefix?
Creates a new deterministic executor with an associated global Tcl command whose name is daName.
This command may be used to invoke various operations on the executor. It has the following
general form:
daName option ?arg arg ...?
Option and the args determine the exact behavior of the command. See section EXECUTOR
METHODS for more explanations.
The executor will be based on the deterministic finite automaton stored in the object fa.
It will keep a copy of the relevant data of the FA in its own storage, in a form easy to
use for its purposes. This also means that changes made to the fa after the construction of
the executor will not influence the executor.
If any has been specified, then the executor will convert all symbols in the input which
are unknown to the base FA to that symbol before proceeding with the processing.
EXECUTOR METHODS
All executors provide the following methods for their manipulation:
daName destroy
Destroys the automaton, including its storage space and associated command.
daName put symbol
Takes the current state of the executor and the symbol and performs the appropriate state
transition. Reports any errors encountered via the command callback, as well as entering a final
state of the underlying FA.
When an error is reported all further invokations of put will do nothing, until the error
condition has been cleared via an invokation of method reset.
daName reset
Unconditionally sets the executor into the start state of the underlying FA. This also clears any
error condition put may have encountered.
daName state
Returns the current state of the underlying FA. This allow for introspection without the need to
pass data from the callback command.
EXECUTOR CALLBACK
The callback command cmdprefix given to an executor via the option -command will be executed by the
object at the global level, using the syntax described below. Note that cmdprefix is not simply the name
of a command, but a full command prefix. In other words it may contain additional fixed argument words
beyond the command word.
cmdprefix error code message
The executor has encountered an error, and message contains a human-readable text explaining the
nature of the problem. The code on the other hand is a fixed machine-readable text. The
following error codes can be generated by executor objects.
BADSYM An unknown symbol was found in the input. This can happen if and only if no -any symbol was
specified.
BADTRANS
The underlying FA has no transition for the current combination of input symbol and state.
In other words, the executor was not able to compute a new state for this combination.
cmdprefix final stateid
The executor has entered the final state stateid.
cmdprefix reset
The executor was reset.
cmdprefix state stateid
The FA changed state due to a transition. stateid is the new state.
EXAMPLES
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please
report such in the category grammar_fa 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
automaton, execution, finite automaton, grammar, parsing, regular expression, regular grammar, regular
languages, running, state, transducer
CATEGORY
Grammars and finite automata
COPYRIGHT
Copyright (c) 2004 Andreas Kupries <andreas_kupries@users.sourceforge.net> Copyright (c) 2007 Bogdan <rftghost@users.sourceforge.net>