grammar::me::cpu::core(n)Grammar operations and usagegrammar::me::cpu::core(n)



______________________________________________________________________________

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_ObjType 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
       functionality 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
              section MATCH PROGRAM REPRESENTATION.

              Each element of the result contains instruction label,
              instruction 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
              PROGRAM 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
              mentioned 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
              locations before the beginning of the stream.

              This utility allows higher levels to convert the location
              offsets found in the error status and the AST into more human
              readable 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
              arguments 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
              grammar::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
              specified 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
              processed. 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
              associated 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
              modifications back into the variable.

              The execution loop will run 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.

   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,
       referenced 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
       absolute 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
       location 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
       status, 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://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::core(n)
