grammar::me::cpu(n)      Grammar operations and usage      grammar::me::cpu(n)



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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

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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

              o      n instructions have been executed, or

              o      a halt instruction was executed, or

              o      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>




grammar_me                            0.2                  grammar::me::cpu(n)
