[comment {-*- tcl -*- doctools manpage}] [manpage_begin grammar::me::cpu n 0.2] [copyright {2005-2006 Andreas Kupries }] [moddesc {Grammar operations and usage}] [titledesc {Virtual machine implementation II for parsing token streams}] [category {Grammars and finite automata}] [require Tcl 8.4] [require grammar::me::cpu [opt 0.2]] [description] [keywords {virtual machine} parsing grammar] [para] This package provides an implementation of the ME virtual machine. Please go and read the document [syscmd grammar::me_intro] first if you do not know what a ME virtual machine is. [para] 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. [para] Internally the package actually uses the value-based machine manipulation commands as provided by the package [package grammar::me::cpu::core] to perform its duties. [section API] [subsection {CLASS API}] The package directly provides only a single command for the construction of ME virtual machines. [list_begin definitions] [call [cmd ::grammar::me::cpu] [arg meName] [arg matchcode]] The command creates a new ME machine object with an associated global Tcl command whose name is [arg meName]. This command may be used to invoke various operations on the machine. It has the following general form: [list_begin definitions] [call [cmd meName] [method option] [opt [arg "arg arg ..."]]] [arg Option] and the [arg arg]s determine the exact behavior of the command. [list_end] [para] The argument [arg matchcode] contains the match instructions the machine has to execute while parsing the input stream. Please read section [sectref-external {MATCH CODE REPRESENTATION}] of the documentation for the package [package grammar::me::cpu::core] for the specification of the structure of this value. [para] The [arg tokmap] argument taken by the implementation provided by the package [package grammar::me::tcl] is here hidden inside of the match instructions and therefore not needed. [list_end] [para] [subsection {OBJECT API}] All ME virtual machine objects created by the class command specified in section [sectref {CLASS API}] support the methods listed below. [para] 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. [list_begin definitions] [call [arg meName] [method lc] [arg 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. [para] [emph 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 [const 0] to [const 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. [call [arg meName] [method tok] [opt "[arg from] [opt [arg to]]"]] This method returns a Tcl list containing the part of the input stream between the locations [arg from] and [arg to] (both inclusive). If [arg to] is not specified it will default to the value of [arg from]. If [arg from] is not specified either the whole input stream is returned. [para] 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 [method lc]. [call [arg meName] [method pc] [arg state]] This method takes the state value of a ME virtual machine and returns the current value of the stored program counter. [call [arg meName] [method iseof] [arg state]] This method takes the state value of a ME virtual machine and returns the current value of the stored eof flag. [call [arg meName] [method at] [arg state]] This method takes the state value of a ME virtual machine and returns the current location in the input stream. [call [arg meName] [method cc] [arg state]] This method takes the state value of a ME virtual machine and returns the current token. [call [arg meName] [method sv]] This command returns the current semantic value [term SV] stored in the machine. This is an abstract syntax tree as specified in the document [syscmd grammar::me_ast], section [sectref-external {AST VALUES}]. [call [arg meName] [method ok]] This method returns the current match status [term OK]. [call [arg meName] [method error]] This method returns the current error status [term ER]. [call [arg meName] [method lstk] [arg state]] This method takes the state value of a ME virtual machine and returns the location stack. [call [arg meName] [method astk] [arg state]] This method takes the state value of a ME virtual machine and returns the AST stack. [call [arg meName] [method mstk] [arg state]] This method takes the state value of a ME virtual machine and returns the AST marker stack. [call [arg meName] [method estk] [arg state]] This method takes the state value of a ME virtual machine and returns the error stack. [call [arg meName] [method rstk] [arg state]] This method takes the state value of a ME virtual machine and returns the subroutine return stack. [call [arg meName] [method nc] [arg state]] This method takes the state value of a ME virtual machine and returns the nonterminal match cache as a dictionary. [call [arg meName] [method ast]] This method returns the current top entry of the AST stack [term AS]. This is an abstract syntax tree as specified in the document [syscmd grammar::me_ast], section [sectref-external {AST VALUES}]. [call [arg meName] [method 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 [method run] the engine will be ignored, until a [method reset] is made. [call [arg meName] [method code]] This method returns the [arg code] information used to construct the object. In other words, the match program executed by the machine. [call [arg meName] [method 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. [call [arg meName] [method put] [arg tok] [arg lex] [arg line] [arg col]] This method adds the token [arg tok] to the end of the input stream, with associated lexeme data [arg lex] and [arg line]/[arg col]umn information. [call [arg meName] [method putstring] [arg string] [arg lvar] [arg cvar]] This method adds each individual character in the [arg 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 [arg lvar] and [arg cvar]. [call [arg meName] [method run] [opt [arg n]]] This methods causes the engine to execute match instructions until either [list_begin itemized] [item] [arg n] instructions have been executed, or [item] a halt instruction was executed, or [item] the input queue is empty and the code is asking for more tokens to process. [list_end] [para] If no limit [arg n] was set only the last two conditions are checked for. [call [arg meName] [method pull] [arg 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 [arg nextcmd] ceases to deliver more tokens. [para] The command prefix [arg 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 [term 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. [para] The end of the input stream for this method does not imply that method [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. [call [arg meName] [method reset]] This method resets the machine to its initial state, discarding any state it may have. [call [arg meName] [method destroy]] This method deletes the object and releases all resurces it claimed. [list_end] [section {BUGS, IDEAS, FEEDBACK}] This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category [emph grammar_me] of the [uri {http://sourceforge.net/tracker/?group_id=12883} {Tcllib SF Trackers}]. Please also report any ideas for enhancements you may have for either package and/or documentation. [manpage_end]