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_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
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, 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(n)
Mac OS X 10.8 - Generated Sun Sep 9 15:25:53 CDT 2012