Provided by: tcllib_1.17-dfsg-1_all 
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 Trackers
[http://core.tcl.tk/tcllib/reportlist]. 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>