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 SF Trackers [
http://sourceforge.net/tracker/?group_id=12883].
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>