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grammar::me::cpu(n) Grammar operations and usage grammar::me::cpu(n)
____________________________________________________________________________________________________________
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 hid-den hidden
den 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 con-taining containing
taining 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 con-vert convert
vert 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 lex-eme, lexeme,
eme, 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 ele-ments elements
ments 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://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(n)
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