Provided by: tcllib_1.17-dfsg-1_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.
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>