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grammar::me::cpu::core(3tGrammar operations and usgrammar::me::cpu::core(3tcl)

______________________________________________________________________________

NAME
       grammar::me::cpu::core - ME virtual machine state manipulation

SYNOPSIS
       package require Tcl  8.4

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

       ::grammar::me::cpu::core disasm asm

       ::grammar::me::cpu::core asm asm

       ::grammar::me::cpu::core new asm

       ::grammar::me::cpu::core lc state location

       ::grammar::me::cpu::core tok state ?from ?to??

       ::grammar::me::cpu::core pc state

       ::grammar::me::cpu::core iseof state

       ::grammar::me::cpu::core at state

       ::grammar::me::cpu::core cc state

       ::grammar::me::cpu::core sv state

       ::grammar::me::cpu::core ok state

       ::grammar::me::cpu::core error state

       ::grammar::me::cpu::core lstk state

       ::grammar::me::cpu::core astk state

       ::grammar::me::cpu::core mstk state

       ::grammar::me::cpu::core estk state

       ::grammar::me::cpu::core rstk state

       ::grammar::me::cpu::core nc state

       ::grammar::me::cpu::core ast state

       ::grammar::me::cpu::core halted state

       ::grammar::me::cpu::core code state

       ::grammar::me::cpu::core eof statevar

       ::grammar::me::cpu::core put statevar tok lex line col

       ::grammar::me::cpu::core run statevar ?n?

_________________________________________________________________

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  represents each ME virtual machine as a Tcl value
       and provides commands to manipulate and query such values to  show  the
       effects	of  executing  instructions,  adding tokens, retrieving state,
       etc.

       The values fully follow the paradigm of	Tcl  that  every  value	 is  a
       string  and while also allowing C implementations for a proper Tcl_Obj‐
       Type to keep all the important data in native data structures.  Because
       of the latter it is recommended to access the state values only through
       the commands of this package to ensure that internal representation  is
       not shimmered away.

       The  actual  structure used by all state values is described in section
       CPU STATE.

API
       The package directly provides only a single command, and all the	 func‐
       tionality is made available through its methods.

       ::grammar::me::cpu::core disasm asm
	      This method returns a list containing a disassembly of the match
	      instructions in asm. The format of asm is specified in the  sec‐
	      tion MATCH PROGRAM REPRESENTATION.

	      Each  element of the result contains instruction label, instruc‐
	      tion name, and the instruction arguments,	 in  this  order.  The
	      label  can  be  the empty string. Jump destinations are shown as
	      labels, strings and tokens unencoded. Token names	 are  prefixed
	      with  their numeric id, if, and only if a tokmap is defined. The
	      two components are separated by a colon.

       ::grammar::me::cpu::core asm asm
	      This method returns code in the format as specified  in  section
	      MATCH  PROGRAM  REPRESENTATION  generated	 from ME assembly code
	      asm, which is in the format as returned by the method disasm.

       ::grammar::me::cpu::core new asm
	      This method creates state value for a ME virtual machine in  its
	      initial state and returns it as its result.

	      The  argument  matchcode	contains  a  Tcl representation of the
	      match instructions the machine has to execute while parsing  the
	      input  stream. Its format is specified in the section MATCH PRO‐
	      GRAM REPRESENTATION.

	      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.

       ::grammar::me::cpu::core lc state location
	      This method takes the state value of a ME	 virtual  machine  and
	      uses  it	to  convert a location in the input stream (as offset)
	      into a line number and column index. The result of the method is
	      a	 2-element  list  containing  the two pieces in the order men‐
	      tioned in the previous sentence.

	      Note that the method cannot convert locations which the  machine
	      has  not	yet read from the input stream. In other words, if the
	      machine has read 7 characters so far it is possible  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	 loca‐
	      tions before the beginning of the stream.

	      This  utility  allows higher levels to convert the location off‐
	      sets found in the error status and the AST into more human read‐
	      able data.

       ::grammar::me::cpu::core tok state ?from ?to??
	      This  method  takes  the state value of a ME virtual machine and
	      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.

	      This  method  places the same restrictions on its location argu‐
	      ments as the method lc.

       ::grammar::me::cpu::core pc state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the current value of the stored program counter.

       ::grammar::me::cpu::core iseof state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the current value of the stored eof flag.

       ::grammar::me::cpu::core at state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the current location in the input stream.

       ::grammar::me::cpu::core cc state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the current token.

       ::grammar::me::cpu::core sv state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns  the  current  semantic  value stored in it.  This is an
	      abstract	syntax	tree  as  specified  in	 the  document	 gram‐
	      mar::me_ast, section AST VALUES.

       ::grammar::me::cpu::core ok state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the match status stored in it.

       ::grammar::me::cpu::core error state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the current error status stored in it.

       ::grammar::me::cpu::core lstk state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the location stack.

       ::grammar::me::cpu::core astk state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the AST stack.

       ::grammar::me::cpu::core mstk state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the AST marker stack.

       ::grammar::me::cpu::core estk state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the error stack.

       ::grammar::me::cpu::core rstk state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the subroutine return stack.

       ::grammar::me::cpu::core nc state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the nonterminal match cache as a dictionary.

       ::grammar::me::cpu::core ast state
	      This  method  takes  the state value of a ME virtual machine and
	      returns the abstract syntax tree currently at the top of the AST
	      stack  stored  in it.  This is an abstract syntax tree as speci‐
	      fied in the document grammar::me_ast, section AST VALUES.

       ::grammar::me::cpu::core halted state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns  the  current  halt  status  stored  in  it, i.e. if the
	      machine has stopped or not.

       ::grammar::me::cpu::core code state
	      This method takes the state value of a ME	 virtual  machine  and
	      returns the code stored in it, i.e. the instructions executed by
	      the machine.

       ::grammar::me::cpu::core eof statevar
	      This method takes the state value of a  ME  virtual  machine  as
	      stored in the variable named by statevar and modifies it so that
	      the eof flag inside is set. This signals	to  the	 machine  that
	      whatever	token  are  in the input queue are the last to be pro‐
	      cessed. There will be no more.

       ::grammar::me::cpu::core put statevar tok lex line col
	      This method takes the state value of a  ME  virtual  machine  as
	      stored in the variable named by statevar and modifies it so that
	      the token tok is added to the end of the input queue, with asso‐
	      ciated lexeme data lex and line/column information.

	      The  operation  will  fail  with an error if the eof flag of the
	      machine has been set through the method eof.

       ::grammar::me::cpu::core run statevar ?n?
	      This method takes the state value of a  ME  virtual  machine  as
	      stored  in  the variable named by statevar, executes a number of
	      instructions and stores the state resulting from their modifica‐
	      tions back into the variable.

	      The execution loop will run 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.

   MATCH PROGRAM REPRESENTATION
       A match program is represented by nested Tcl list. The  first  element,
       asm,  is	 a  list  of integer numbers, the instructions to execute, and
       their arguments. The second element, pool, is a list of strings, refer‐
       enced  by  the  instructions, for error messages, token names, etc. The
       third element, tokmap, provides ordering information  for  the  tokens,
       mapping their names to their numerical rank. This element can be empty,
       forcing lexicographic comparison when matching ranges.

       All ME instructions are encoded as integer numbers,  with  the  mapping
       given  below.  A	 number	 of the instructions, those which handle error
       messages, have been given an additional argument to supply that message
       explicitly instead of having it constructed from token names, etc. This
       allows the machine state to store only the message ids instead  of  the
       full strings.

       Jump  destination  arguments are absolute indices into the asm element,
       refering to the instruction to jump to. Any string arguments are	 abso‐
       lute  indices  into the pool element. Tokens, characters, messages, and
       token (actually character) classes to match  are	 coded	as  references
       into the pool as well.

       [1]    "ict_advance message"

       [2]    "ict_match_token tok message"

       [3]    "ict_match_tokrange tokbegin tokend message"

       [4]    "ict_match_tokclass code message"

       [5]    "inc_restore branchlabel nt"

       [6]    "inc_save nt"

       [7]    "icf_ntcall branchlabel"

       [8]    "icf_ntreturn"

       [9]    "iok_ok"

       [10]   "iok_fail"

       [11]   "iok_negate"

       [12]   "icf_jalways branchlabel"

       [13]   "icf_jok branchlabel"

       [14]   "icf_jfail branchlabel"

       [15]   "icf_halt"

       [16]   "icl_push"

       [17]   "icl_rewind"

       [18]   "icl_pop"

       [19]   "ier_push"

       [20]   "ier_clear"

       [21]   "ier_nonterminal message"

       [22]   "ier_merge"

       [23]   "isv_clear"

       [24]   "isv_terminal"

       [25]   "isv_nonterminal_leaf nt"

       [26]   "isv_nonterminal_range nt"

       [27]   "isv_nonterminal_reduce nt"

       [28]   "ias_push"

       [29]   "ias_mark"

       [30]   "ias_mrewind"

       [31]   "ias_mpop"

CPU STATE
       A state value is a list containing the following elements, in the order
       listed below:

       [1]    code: Match instructions, see MATCH PROGRAM REPRESENTATION.

       [2]    pc:   Program counter, int.

       [3]    halt: Halt flag, boolean.

       [4]    eof:  Eof flag, boolean

       [5]    tc:   Terminal cache, and input queue. Structure see below.

       [6]    cl:   Current location, int.

       [7]    ct:   Current token, string.

       [8]    ok:   Match status, boolean.

       [9]    sv:   Semantic value, list.

       [10]   er:   Error status, list.

       [11]   ls:   Location stack, list.

       [12]   as:   AST stack, list.

       [13]   ms:   AST marker stack, list.

       [14]   es:   Error stack, list.

       [15]   rs:   Return stack, list.

       [16]   nc:   Nonterminal cache, dictionary.

       tc, the input queue of tokens waiting for processing and	 the  terminal
       cache  containing  the  tokens  already processing are one unified data
       structure simply holding all tokens and	their  information,  with  the
       current	location  separating  that  which has been processed from that
       which is waiting.  Each element of the queue/cache is a list containing
       the  token,  its	 lexeme information, line number, and column index, in
       this order.

       All stacks have their top element aat the end, i.e. pushing an item  is
       equivalent to appending to the list representing the stack, and popping
       it removes the last element.

       er, the error status is either empty or a list of two elements, a loca‐
       tion  in	 the input, and a list of messages, encoded as references into
       the pool element of the code.

       nc, the nonterminal cache is keyed by nonterminal  name	and  location,
       each  value a four-element list containing current location, match sta‐
       tus, semantic value, and error status, in this order.

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://source‐
       forge.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::core(3tcl)
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