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grammar::fa::dexec(n)               Finite automaton operations and usage              grammar::fa::dexec(n)



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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 deterministic finite automatons (DFA).
       Executors are objects which are given a string of symbols in a piecemal fashion, perform state  tran-sitions transitions
       sitions 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 fol-lowing following
              lowing 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 con-dition condition
              dition 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 combi-nation. combination.
                     nation.

       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://source -
       forge.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, regu-lar regular
       lar 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>




grammar_fa                                           0.2                               grammar::fa::dexec(n)