--- name: "dexec" section: "3tcl" platform: "linux" package: "tcllib" version: "2.0+dfsg-4" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/dexec" --- # dexec(3tcl) Execute deterministic finite automatons ``` ``` ## NAME grammar::fa::dexec - Execute deterministic finite automatons ## SYNOPSIS package require **Tcl 8.5 9** package require **snit** package require **grammar::fa::dexec ?0.3?** **::grammar::fa::dexec** *daName* *fa* ?**-any** *any*? ?**-command** *cmdprefix*? **daName** *option* ?*arg arg ...*? *daName* **destroy** *daName* **put** *symbol* *daName* **reset** *daName* **state** *cmdprefix* **error** *code* *message* *cmdprefix* **final** *stateid* *cmdprefix* **reset** *cmdprefix* **state** *stateid* ``` ``` ## DESCRIPTION This package provides a class for executors constructed from deterministic *finite automatons* (DFA). Executors are objects which are given a string of symbols in a piecemal fashion, perform state transitions and report back when they enter a final state, or find an error in the input. For the actual creation of the DFAs the executors are based on we have the packages **grammar::fa** and **grammar::fa::op**. The objects follow a push model. Symbols are pushed into the executor, and when something important happens, i.e. error occurs, a state transition, or a final state is entered this will be reported via the callback specified via the option **-command**. Note that conversion of this into a pull model where the environment retrieves messages from the object and the object uses a callback to ask for more symbols is a trivial thing. *Side note*: The acceptor objects provided by **grammar::fa::dacceptor** could have been implemented on top of the executors provided here, but were not, to get a bit more performance (we avoid a number of method calls and the time required for their dispatch). ## API The package exports the API described here. - **::grammar::fa::dexec** *daName* *fa* ?**-any** *any*? ?**-command** *cmdprefix*? Creates a new deterministic executor with an associated global Tcl command whose name is *daName*. This command may be used to invoke various operations on the executor. It has the following general form: - **daName** *option* ?*arg arg ...*? *Option* and the *arg*s determine the exact behavior of the command. See section **EXECUTOR METHODS** for more explanations. The executor will be based on the deterministic finite automaton stored in the object *fa*. It will keep a copy of the relevant data of the FA in its own storage, in a form easy to use for its purposes. This also means that changes made to the *fa* after the construction of the executor *will not* influence the executor. If *any* has been specified, then the executor will convert all symbols in the input which are unknown to the base FA to that symbol before proceeding with the processing. ## EXECUTOR METHODS All executors provide the following methods for their manipulation: - *daName* **destroy** Destroys the automaton, including its storage space and associated command. - *daName* **put** *symbol* Takes the current state of the executor and the *symbol* and performs the appropriate state transition. Reports any errors encountered via the command callback, as well as entering a final state of the underlying FA. When an error is reported all further invokations of **put** will do nothing, until the error condition has been cleared via an invokation of method **reset**. - *daName* **reset** Unconditionally sets the executor into the start state of the underlying FA. This also clears any error condition **put** may have encountered. - *daName* **state** Returns the current state of the underlying FA. This allow for introspection without the need to pass data from the callback command. ## EXECUTOR CALLBACK The callback command *cmdprefix* given to an executor via the option **-command** will be executed by the object at the global level, using the syntax described below. Note that *cmdprefix* is not simply the name of a command, but a full command prefix. In other words it may contain additional fixed argument words beyond the command word. - *cmdprefix* **error** *code* *message* The executor has encountered an error, and *message* contains a human-readable text explaining the nature of the problem. The *code* on the other hand is a fixed machine-readable text. The following error codes can be generated by executor objects. - **BADSYM** An unknown symbol was found in the input. This can happen if and only if no **-any** symbol was specified. - **BADTRANS** The underlying FA has no transition for the current combination of input symbol and state. In other words, the executor was not able to compute a new state for this combination. - *cmdprefix* **final** *stateid* The executor has entered the final state *stateid*. - *cmdprefix* **reset** The executor was reset. - *cmdprefix* **state** *stateid* The FA changed state due to a transition. *stateid* is the new state. ## EXAMPLES ## BUGS, IDEAS, FEEDBACK This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category *grammar\_fa* 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. When proposing code changes, please provide *unified diffs*, i.e the output of **diff -u**. Note further that *attachments* are strongly preferred over inlined patches. Attachments can be made by going to the **Edit** form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar. ## KEYWORDS automaton, execution, finite automaton, grammar, parsing, regular expression, regular grammar, regular languages, running, state, transducer ## CATEGORY Grammars and finite automata ## COPYRIGHT ``` Copyright (c) 2004 Andreas Kupries Copyright (c) 2007 Bogdan ```