Provided by: tcllib_1.14-dfsg-1_all bug

NAME

       grammar::me::cpu - Virtual machine implementation II for parsing token streams

SYNOPSIS

       package require Tcl  8.4

       package require grammar::me::cpu  ?0.2?

       ::grammar::me::cpu meName matchcode

       meName option ?arg arg ...?

       meName lc location

       meName tok ?from ?to??

       meName pc state

       meName iseof state

       meName at state

       meName cc state

       meName sv

       meName ok

       meName error

       meName lstk state

       meName astk state

       meName mstk state

       meName estk state

       meName rstk state

       meName nc state

       meName ast

       meName halted

       meName code

       meName eof

       meName put tok lex line col

       meName putstring string lvar cvar

       meName run ?n?

       meName pull nextcmd

       meName reset

       meName destroy

_________________________________________________________________

DESCRIPTION

       This package provides an implementation of the ME virtual machine.  Please go and read the
       document grammar::me_intro first if you do not know what a ME virtual machine is.

       This implementation provides an object-based API and the machines are not  truly  tied  to
       Tcl. A C implementation of the same API is quite possible.

       Internally  the  package  actually  uses  the value-based machine manipulation commands as
       provided by the package grammar::me::cpu::core to perform its duties.

API

   CLASS API
       The package directly provides only a single command for the  construction  of  ME  virtual
       machines.

       ::grammar::me::cpu meName matchcode
              The  command  creates a new ME machine object with an associated global Tcl command
              whose name is meName. This command may be used to invoke various operations on  the
              machine.  It has the following general form:

              meName option ?arg arg ...?
                     Option and the args determine the exact behavior of the command.

       The  argument  matchcode  contains the match instructions the machine has to execute while
       parsing  the  input  stream.  Please  read  section  MATCH  CODE  REPRESENTATION  of   the
       documentation  for  the  package  grammar::me::cpu::core  for  the  specification  of  the
       structure of this value.

       The tokmap argument taken by the implementation provided by the  package  grammar::me::tcl
       is here hidden inside of the match instructions and therefore not needed.

   OBJECT API
       All ME virtual machine objects created by the class command specified in section CLASS API
       support the methods listed below.

       The machines provided by this package provide methods for  operation  in  both  push-  and
       pull-styles.  Push-style  means  that  tokens  are pushed into the machine state when they
       arrive, triggering further execution until they are consumed. In other words, this  allows
       the  machine  to  be  suspended  and resumed at will and an arbitrary number of times, the
       quasi-parallel operation of several machines, and the operation as part of the event loop.

       meName lc location
              This method converts the location of a token given as offset in  the  input  stream
              into  the  associated  line number and column index. The result of the command is a
              2-element list containing the two values, in the order mentioned  in  the  previous
              sentence.   This  allows higher levels to convert the location information found in
              the error status and the generated AST into more human readable data.

              Note that the command is not able to convert locations which have not been  reached
              by the machine yet. In other words, if the machine has read 7 tokens the command is
              able to convert the offsets 0 to 6, but nothing beyond that. This also  shows  that
              it is not possible to convert offsets which refer to locations before the beginning
              of the stream.

       meName tok ?from ?to??
              This method returns a Tcl list containing the part of the input stream between  the
              locations  from  and to (both inclusive). If to is not specified it will default to
              the value of from.  If from is not specified  either  the  whole  input  stream  is
              returned.

              Each  element  of  the  returned  list  is  a list of four elements, the token, its
              associated lexeme, line number, and column index,  in  this  order.   This  command
              places the same restrictions on its location arguments as the method lc.

       meName pc state
              This  method  takes the state value of a ME virtual machine and returns the current
              value of the stored program counter.

       meName iseof state
              This method takes the state value of a ME virtual machine and returns  the  current
              value of the stored eof flag.

       meName at state
              This  method  takes the state value of a ME virtual machine and returns the current
              location in the input stream.

       meName cc state
              This method takes the state value of a ME virtual machine and returns  the  current
              token.

       meName sv
              This  command  returns the current semantic value SV stored in the machine. This is
              an abstract syntax tree as specified in the document grammar::me_ast,  section  AST
              VALUES.

       meName ok
              This method returns the current match status OK.

       meName error
              This method returns the current error status ER.

       meName lstk state
              This  method takes the state value of a ME virtual machine and returns the location
              stack.

       meName astk state
              This method takes the state value of a ME  virtual  machine  and  returns  the  AST
              stack.

       meName mstk state
              This  method  takes  the  state  value  of a ME virtual machine and returns the AST
              marker stack.

       meName estk state
              This method takes the state value of a ME virtual machine  and  returns  the  error
              stack.

       meName rstk state
              This  method  takes  the  state  value  of  a  ME  virtual  machine and returns the
              subroutine return stack.

       meName nc state
              This method takes the  state  value  of  a  ME  virtual  machine  and  returns  the
              nonterminal match cache as a dictionary.

       meName ast
              This method returns the current top entry of the AST stack AS.  This is an abstract
              syntax tree as specified in the document grammar::me_ast, section AST VALUES.

       meName halted
              This method returns a boolean value telling  the  caller  whether  the  engine  has
              halted  execution  or not. Halt means that no further matching is possible, and the
              information retrieved via the other method is final. Attempts  to  run  the  engine
              will be ignored, until a reset is made.

       meName code
              This  method  returns  the  code information used to construct the object. In other
              words, the match program executed by the machine.

       meName eof
              This method adds an end of file marker to  the  end  of  the  input  stream.   This
              signals  the  machine  that  the  current contents of the input queue are the final
              parts of the input and nothing will come after. Attempts  to  put  more  characters
              into the queue will fail.

       meName put tok lex line col
              This  method  adds  the  token  tok to the end of the input stream, with associated
              lexeme data lex and line/column information.

       meName putstring string lvar cvar
              This method adds each individual character in the string as a token to the  end  of
              the  input  stream,  from first to last. The lexemes will be empty and the line/col
              information is computed based on the characters encountered and  the  data  in  the
              variables lvar and cvar.

       meName run ?n?
              This methods causes the engine to execute match instructions until either

              ·      n instructions have been executed, or

              ·      a halt instruction was executed, or

              ·      the input queue is empty and the code is asking for more tokens to process.

       If no limit n was set only the last two conditions are checked for.

       meName pull nextcmd
              This method implements pull-style operation of the machine. It causes it to execute
              match instructions until either a halt  instruction  is  reached,  or  the  command
              prefix nextcmd ceases to deliver more tokens.

              The command prefix nextcmd represents the input stream of characters and is invoked
              by the machine whenever the a new  character  from  the  stream  is  required.  The
              instruction  for  handling  this is ict_advance.  The callback has to return either
              the empty list, or a list of 4 elements containing the token, its lexeme attribute,
              and its location as line number and column index, in this order.  The empty list is
              the signal that the end of the input stream has been reached. The lexeme  attribute
              is stored in the terminal cache, but otherwise not used by the machine.

              The  end  of  the  input  stream  for this method does not imply that method eof is
              called for the machine as a whole.  By  avoiding  this  and  still  asking  for  an
              explicit  call  of  the method it is possible to mix push- and pull-style operation
              during the lifetime of the machine.

       meName reset
              This method resets the machine to its initial state, discarding any  state  it  may
              have.

       meName destroy
              This method deletes the object and releases all resurces it claimed.

BUGS, IDEAS, FEEDBACK

       This  document,  and  the  package  it  describes, will undoubtedly contain bugs and other
       problems.  Please report such in  the  category  grammar_me  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

       grammar, parsing, virtual machine

CATEGORY

       Grammars and finite automata

COPYRIGHT

       Copyright (c) 2005-2006 Andreas Kupries <andreas_kupries@users.sourceforge.net>