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pt_peg_op(i) Parser Tools pt_peg_op(i) 





NAME


pt_peg_op - Parser Tools PE Grammar Utility Operations






SYNOPSIS


package require Tcl 8.5


package require pt::peg::op ?1.1.0?


::peg::peg::op called container


::peg::peg::op dechain container


::peg::peg::op drop unreachable container


::peg::peg::op drop unrealizable
  container


::peg::peg::op flatten container


::peg::peg::op minimize container


::peg::peg::op modeopt container


::peg::peg::op reachable container


::peg::peg::op realizable container










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. 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.

  

  
::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.



  
::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.

  

  
::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.

  

  
::peg::peg::op flatten container

  
This command flattens (see pt::pe::op) 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.

  

  
::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.

  

  
::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.

  
[2]

  
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.



  
::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.

  

  
::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.

  








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, LL(k), PEG, TDPL, context-free languages, expression,
    grammar, matching, parser, parsing expression, parsing expression grammar,
    push down automaton, recursive descent, state, top-down parsing languages,
    transducer






CATEGORY


Parsing and Grammars






COPYRIGHT


Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>








  

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