[//000000001]: # (pt\_peg\_op \- Parser Tools) [//000000002]: # (Generated from file 'pt\_peg\_op\.man' by tcllib/doctools with format 'markdown') [//000000003]: # (Copyright © 2009 Andreas Kupries ) [//000000004]: # (pt\_peg\_op\(i\) 1\.1\.0 tcllib "Parser Tools")
[ Main Table Of Contents | Table Of Contents | Keyword Index | Categories | Modules | Applications ]
# NAME pt\_peg\_op \- Parser Tools PE Grammar Utility Operations # Table Of Contents - [Table Of Contents](#toc) - [Synopsis](#synopsis) - [Description](#section1) - [API](#section2) - [Bugs, Ideas, Feedback](#section3) - [Keywords](#keywords) - [Category](#category) - [Copyright](#copyright) # SYNOPSIS package require Tcl 8\.5 package require pt::peg::op ?1\.1\.0? [__::peg::peg::op__ __called__ *container*](#1) [__::peg::peg::op__ __dechain__ *container*](#2) [__::peg::peg::op__ __drop unreachable__ *container*](#3) [__::peg::peg::op__ __drop unrealizable__ *container*](#4) [__::peg::peg::op__ __flatten__ *container*](#5) [__::peg::peg::op__ __minimize__ *container*](#6) [__::peg::peg::op__ __modeopt__ *container*](#7) [__::peg::peg::op__ __reachable__ *container*](#8) [__::peg::peg::op__ __realizable__ *container*](#9) # DESCRIPTION Are you lost ? Do you have trouble understanding this document ? In that case please read the overview provided by the *[Introduction to Parser Tools](pt\_introduction\.md)*\. This document is the entrypoint to the whole system the current package is a part of\. This package provides a number of utility commands manipulating a PE grammar \(container\) in various ways\. # API - __::peg::peg::op__ __called__ *container* This command determines the static call structure for the nonterminal symbols of the grammar stored in the *container*\. The result of the command is a dictionary mapping from each symbol to the symbols it calls\. The empty string is the key used to represent the start expression of the grammar\. The grammar in the container is not modified\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __dechain__ *container* This command simplifies all symbols which just chain to a different symbol by inlining the right hand side of the called symbol in its callers\. This works if and only the modes match properly, per the decision table below\. caller called | dechain | notes --------------+---------+----------------------- value value | yes | value is passed value leaf | yes | value is passed value void | yes | caller is implied void leaf value | no | generated value was discarded, inlined would not. called may be implied void. leaf leaf | no | s.a. leaf void | no | s.a. void value | no | caller drops value, inlined would not. void leaf | no | s.a. void void | yes | The result of the command is the empty string\. The grammar in the container is directly modified\. If that is not wanted, a copy of the original container has to be used\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __drop unreachable__ *container* This command removes all symbols from the grammar which are not __reachable__\. The result of the command is the empty string\. The grammar in the container is directly modified\. If that is not wanted, a copy of the original container has to be used\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __drop unrealizable__ *container* This command removes all symbols from the grammar which are not __realizable__\. The result of the command is the empty string\. The grammar in the container is directly modified\. If that is not wanted, a copy of the original container has to be used\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __flatten__ *container* This command flattens \(see __[pt::pe::op](pt\_pexpr\_op\.md)__\) all expressions in the grammar, i\.e\. the start expression and the right hand sides of all nonterminal symbols\. The result of the command is the empty string\. The grammar in the container is directly modified\. If that is not wanted, a copy of the original container has to be used\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __minimize__ *container* This command reduces the provided grammar by applying most of the other methods of this package\. After flattening the expressions it removes unreachable and unrealizable symbols, flattens the expressions again, then optimizes the symbol modes before collapsing symbol chains as much as possible\. The result of the command is the empty string\. The grammar in the container is directly modified\. If that is not wanted, a copy of the original container has to be used\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __modeopt__ *container* This command optimizes the semantic modes of non\-terminal symbols according to the two rules below\. 1. If a symbol X with mode __value__ calls no other symbols, i\.e\. uses only terminal symbols in whatever combination, then this can be represented simpler by using mode __leaf__\. 1. If a symbol X is only called from symbols with modes __leaf__ or __void__ then this symbol should have mode __void__ also, as any AST it could generate will be discarded anyway\. The result of the command is the empty string\. The grammar in the container is directly modified\. If that is not wanted, a copy of the original container has to be used\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __reachable__ *container* This command computes the set of all nonterminal symbols which are reachable from the start expression of the grammar\. This is essentially the transitive closure over __called__ and the symbol's right hand sides, beginning with the start expression\. The result of the command is the list of reachable symbols\. The grammar in the container is not modified\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. - __::peg::peg::op__ __realizable__ *container* This command computes the set of all nonterminal symbols which are realizable, i\.e\. can derive pure terminal phrases\. This is done iteratively, starting with state unrealizable for all and any, and then updating all symbols which are realizable, propagating changes, until nothing changes any more\. The result of the command is the list of realizable symbols\. The grammar in the container is not modified\. The *container* instance has to expose a method API as is provided by the package __[pt::peg::container](pt\_peg\_container\.md)__\. # Bugs, Ideas, Feedback This document, and the package it describes, will undoubtedly contain bugs and other problems\. Please report such in the category *pt* 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 [EBNF](\.\./\.\./\.\./\.\./index\.md\#ebnf), [LL\(k\)](\.\./\.\./\.\./\.\./index\.md\#ll\_k\_), [PEG](\.\./\.\./\.\./\.\./index\.md\#peg), [TDPL](\.\./\.\./\.\./\.\./index\.md\#tdpl), [context\-free languages](\.\./\.\./\.\./\.\./index\.md\#context\_free\_languages), [expression](\.\./\.\./\.\./\.\./index\.md\#expression), [grammar](\.\./\.\./\.\./\.\./index\.md\#grammar), [matching](\.\./\.\./\.\./\.\./index\.md\#matching), [parser](\.\./\.\./\.\./\.\./index\.md\#parser), [parsing expression](\.\./\.\./\.\./\.\./index\.md\#parsing\_expression), [parsing expression grammar](\.\./\.\./\.\./\.\./index\.md\#parsing\_expression\_grammar), [push down automaton](\.\./\.\./\.\./\.\./index\.md\#push\_down\_automaton), [recursive descent](\.\./\.\./\.\./\.\./index\.md\#recursive\_descent), [state](\.\./\.\./\.\./\.\./index\.md\#state), [top\-down parsing languages](\.\./\.\./\.\./\.\./index\.md\#top\_down\_parsing\_languages), [transducer](\.\./\.\./\.\./\.\./index\.md\#transducer) # CATEGORY Parsing and Grammars # COPYRIGHT Copyright © 2009 Andreas Kupries