grammar::fa::dexec(3tFinite automaton operations and ugrammar::fa::dexec(3tcl)
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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
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DESCRIPTION
This package provides a class for executors constructed from determin-
istic 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 in-
put. 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 tran-
sition, or a final state is entered this will be reported via the call-
back specified via the option -command. Note that conversion of this
into a pull model where the environment retrieves messages from the ob-
ject and the object uses a callback to ask for more symbols is a triv-
ial 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 explana-
tions.
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 ex-
ecutor 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 associ-
ated command.
daName put symbol
Takes the current state of the executor and the symbol and per-
forms the appropriate state transition. Reports any errors en-
countered 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 in-
vokation 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 addi-
tional 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 com-
bination 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 out-
put 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 ex-
pression, regular grammar, regular languages, running, state, trans-
ducer
CATEGORY
Grammars and finite automata
COPYRIGHT
Copyright (c) 2004 Andreas Kupries <andreas_kupries@users.sourceforge.net>
Copyright (c) 2007 Bogdan <rftghost@users.sourceforge.net>
tcllib 0.2 grammar::fa::dexec(3tcl)