pt::peg::export::container(n) Parser Tools pt::peg::export::container(n) 







pt::peg::export::container - PEG Export Plugin. Write CONTAINER
    format








package require Tcl 8.5


package require pt::peg::export::container ?1?


package require pt::peg::to::container 


export serial configuration












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 implements the parsing expression grammar export
    plugin for the generation of CONTAINER markup.


It resides in the Export section of the Core Layer of Parser Tools
    and is intended to be used by pt::peg::export, the export manager,
    sitting between it and the corresponding core conversion functionality
    provided by pt::peg::to::container.


IMAGE: arch_core_eplugins


While the direct use of this package with a regular interpreter is
    possible, this is strongly disrecommended and requires a number of
    contortions to provide the expected environment. The proper way to use this
    functionality depends on the situation:



  
[1]

  
In an untrusted environment the proper access is through the package
      pt::peg::export and the export manager objects it provides.

  
[2]

  
In a trusted environment however simply use the package
      pt::peg::to::container and access the core conversion functionality
      directly.










The API provided by this package satisfies the specification of
    the Plugin API found in the Parser Tools Export API
  specification.



  

  
This command takes the canonical serialization of a parsing expression
      grammar, as specified in section PEG serialization format, and
      contained in serial, the configuration, a dictionary, and
      generates CONTAINER markup encoding the grammar. The created string is
      then returned as the result of the command.










The CONTAINER export plugin recognizes the following configuration
    variables and changes its behaviour as they specify.



  

  
The value of this configuration variable controls which methods of
      pt::peg instances the plugin will use to specify the grammar. There
      are two legal values







  

  
In this mode the methods start, add, modes, and
      rules are used to specify the grammar in a bulk manner, i.e. as a
      set of nonterminal symbols, and two dictionaries mapping from the symbols
      to their semantic modes and parsing expressions.
    
This mode is the default.

  

  

  
In this mode the methods start, add, mode, and
      rule are used to specify the grammar piecemal, with each
      nonterminal having its own block of defining commands.







  

  
If this configuration variable is set it is assumed to contain a string
      into which to put the generated code and other configuration data. The
      various locations are expected to be specified with the following
      placeholders:







  
@user@

  
To be replaced with the value of the configuration variable
    user.

  
@format@

  
To be replaced with the the constant CONTAINER.

  
@file@

  
To be replaced with the value of the configuration variable
    file.

  
@name@

  
To be replaced with the value of the configuration variable
    name.

  
@mode@

  
To be replaced with the value of the configuration variable
    mode.

  
@code@

  
To be replaced with the generated code.






If this configuration variable is not set, or empty, then the
    plugin falls back to a standard template, which is defined as
    "@code@".


Note that this plugin may ignore the standard configuration
    variables user, format, file, and their values,
    depending on the chosen template.


The content of the standard configuration variable name, if
    set, is used as name of the grammar in the output. Otherwise the plugin
    falls back to the default name a_pe_grammar.








The container format is another form of describing parsing
    expression grammars. While data in this format is executable it does not
    constitute a parser for the grammar. It always has to be used in conjunction
    with the package pt::peg::interp, a grammar interpreter.


The format represents grammars by a snit::type, i.e. class,
    whose instances are API-compatible to the instances of the
    pt::peg::container package, and which are preloaded with the grammar
    in question.


It has no direct formal specification beyond what was said
  above.






Assuming the following PEG for simple mathematical expressions




PEG calculator (Expression)


    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'	;


    Sign       <- '-' / '+'					;


    Number     <- Sign? Digit+					;


    Expression <- '(' Expression ')' / (Factor (MulOp Factor)*)	;


    MulOp      <- '*' / '/'					;


    Factor     <- Term (AddOp Term)*				;


    AddOp      <- '+'/'-'					;


    Term       <- Number					;
END;



one possible CONTAINER serialization for it is




snit::type a_pe_grammar {


    constructor {} {


        install myg using pt::peg::container ${selfns}::G


        $myg start {n Expression}


        $myg add   AddOp Digit Expression Factor MulOp Number Sign Term


        $myg modes {


            AddOp      value


            Digit      value


            Expression value


            Factor     value


            MulOp      value


            Number     value


            Sign       value


            Term       value


        }


        $myg rules {


            AddOp      {/ {t -} {t +}}


            Digit      {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}


            Expression {/ {x {t \50} {n Expression} {t \51}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}


            Factor     {x {n Term} {* {x {n AddOp} {n Term}}}}


            MulOp      {/ {t *} {t /}}


            Number     {x {? {n Sign}} {+ {n Digit}}}


            Sign       {/ {t -} {t +}}


            Term       {n Number}


        }


        return


    }


    component myg


    delegate method * to myg
}











Here we specify the format used by the Parser Tools to serialize
    Parsing Expression Grammars as immutable values for transport, comparison,
    etc.


We distinguish between regular and canonical
    serializations. While a PEG may have more than one regular serialization
    only exactly one of them will be canonical.



  

  







  
[1]

  
The serialization of any PEG is a nested Tcl dictionary.

  
[2]

  
This dictionary holds a single key, pt::grammar::peg, and its
      value. This value holds the contents of the grammar.

  
[3]

  
The contents of the grammar are a Tcl dictionary holding the set of
      nonterminal symbols and the starting expression. The relevant keys and
      their values are







  

  
The value is a Tcl dictionary whose keys are the names of the nonterminal
      symbols known to the grammar.







  
[1]

  
Each nonterminal symbol may occur only once.

  
[2]

  
The empty string is not a legal nonterminal symbol.

  
[3]

  
The value for each symbol is a Tcl dictionary itself. The relevant keys
      and their values in this dictionary are







  

  
The value is the serialization of the parsing expression describing the
      symbols sentennial structure, as specified in the section PE
      serialization format.

  

  
The value can be one of three values specifying how a parser should handle
      the semantic value produced by the symbol.







  

  
The semantic value of the nonterminal symbol is an abstract syntax tree
      consisting of a single node node for the nonterminal itself, which has the
      ASTs of the symbol's right hand side as its children.

  

  
The semantic value of the nonterminal symbol is an abstract syntax tree
      consisting of a single node node for the nonterminal, without any
      children. Any ASTs generated by the symbol's right hand side are
      discarded.

  

  
The nonterminal has no semantic value. Any ASTs generated by the symbol's
      right hand side are discarded (as well).











  

  
The value is the serialization of the start parsing expression of the
      grammar, as specified in the section PE serialization format.







  
[4]

  
The terminal symbols of the grammar are specified implicitly as the set of
      all terminal symbols used in the start expression and on the RHS of the
      grammar rules.







  

  
The canonical serialization of a grammar has the format as specified in
      the previous item, and then additionally satisfies the constraints below,
      which make it unique among all the possible serializations of this
      grammar.







  
[1]

  
The keys found in all the nested Tcl dictionaries are sorted in ascending
      dictionary order, as generated by Tcl's builtin command lsort
      -increasing -dict.

  
[2]

  
The string representation of the value is the canonical representation of
      a Tcl dictionary. I.e. it does not contain superfluous whitespace.










Assuming the following PEG for simple mathematical expressions




PEG calculator (Expression)


    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'	;


    Sign       <- '-' / '+'					;


    Number     <- Sign? Digit+					;


    Expression <- '(' Expression ')' / (Factor (MulOp Factor)*)	;


    MulOp      <- '*' / '/'					;


    Factor     <- Term (AddOp Term)*				;


    AddOp      <- '+'/'-'					;


    Term       <- Number					;
END;



then its canonical serialization (except for whitespace) is




pt::grammar::peg {


    rules {
	AddOp      {is {/ {t -} {t +}}                                                                mode value}
	Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}
	Expression {is {/ {x {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}} mode value}
	Factor     {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
	MulOp      {is {/ {t *} {t /}}                                                                mode value}
	Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}
	Sign       {is {/ {t -} {t +}}                                                                mode value}
	Term       {is  {n Number}                                                                    mode value}


    }


    start {n Expression}
}











Here we specify the format used by the Parser Tools to serialize
    Parsing Expressions as immutable values for transport, comparison, etc.


We distinguish between regular and canonical
    serializations. While a parsing expression may have more than one regular
    serialization only exactly one of them will be canonical.



  

  







  

  







  
[1]

  
The string epsilon is an atomic parsing expression. It matches the
      empty string.

  
[2]

  
The string dot is an atomic parsing expression. It matches any
      character.

  
[3]

  
The string alnum is an atomic parsing expression. It matches any
      Unicode alphabet or digit character. This is a custom extension of PEs
      based on Tcl's builtin command string is.

  
[4]

  
The string alpha is an atomic parsing expression. It matches any
      Unicode alphabet character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[5]

  
The string ascii is an atomic parsing expression. It matches any
      Unicode character below U0080. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[6]

  
The string control is an atomic parsing expression. It matches any
      Unicode control character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[7]

  
The string digit is an atomic parsing expression. It matches any
      Unicode digit character. Note that this includes characters outside of the
      [0..9] range. This is a custom extension of PEs based on Tcl's builtin
      command string is.

  
[8]

  
The string graph is an atomic parsing expression. It matches any
      Unicode printing character, except for space. This is a custom extension
      of PEs based on Tcl's builtin command string is.

  
[9]

  
The string lower is an atomic parsing expression. It matches any
      Unicode lower-case alphabet character. This is a custom extension of PEs
      based on Tcl's builtin command string is.

  
[10]

  
The string print is an atomic parsing expression. It matches any
      Unicode printing character, including space. This is a custom extension of
      PEs based on Tcl's builtin command string is.

  
[11]

  
The string punct is an atomic parsing expression. It matches any
      Unicode punctuation character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[12]

  
The string space is an atomic parsing expression. It matches any
      Unicode space character. This is a custom extension of PEs based on Tcl's
      builtin command string is.

  
[13]

  
The string upper is an atomic parsing expression. It matches any
      Unicode upper-case alphabet character. This is a custom extension of PEs
      based on Tcl's builtin command string is.

  
[14]

  
The string wordchar is an atomic parsing expression. It matches any
      Unicode word character. This is any alphanumeric character (see alnum),
      and any connector punctuation characters (e.g. underscore). This is a
      custom extension of PEs based on Tcl's builtin command string
    is.

  
[15]

  
The string xdigit is an atomic parsing expression. It matches any
      hexadecimal digit character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[16]

  
The string ddigit is an atomic parsing expression. It matches any
      decimal digit character. This is a custom extension of PEs based on Tcl's
      builtin command regexp.

  
[17]

  
The expression [list t x] is an atomic parsing expression. It
      matches the terminal string x.

  
[18]

  
The expression [list n A] is an atomic parsing expression. It
      matches the nonterminal A.







  

  







  
[1]

  
For parsing expressions e1, e2, ... the result of [list /
      e1 e2 ... ] is a parsing expression as well. This is the
      ordered choice, aka prioritized choice.

  
[2]

  
For parsing expressions e1, e2, ... the result of [list x
      e1 e2 ... ] is a parsing expression as well. This is the
      sequence.

  
[3]

  
For a parsing expression e the result of [list * e] is a
      parsing expression as well. This is the kleene closure, describing
      zero or more repetitions.

  
[4]

  
For a parsing expression e the result of [list + e] is a
      parsing expression as well. This is the positive kleene closure,
      describing one or more repetitions.

  
[5]

  
For a parsing expression e the result of [list & e] is a
      parsing expression as well. This is the and lookahead
    predicate.

  
[6]

  
For a parsing expression e the result of [list ! e] is a
      parsing expression as well. This is the not lookahead
    predicate.

  
[7]

  
For a parsing expression e the result of [list ? e] is a
      parsing expression as well. This is the optional input.









  

  
The canonical serialization of a parsing expression has the format as
      specified in the previous item, and then additionally satisfies the
      constraints below, which make it unique among all the possible
      serializations of this parsing expression.







  
[1]

  
The string representation of the value is the canonical representation of
      a pure Tcl list. I.e. it does not contain superfluous whitespace.

  
[2]

  
Terminals are not encoded as ranges (where start and end of the
      range are identical).










Assuming the parsing expression shown on the right-hand side of
    the rule






    Expression <- '(' Expression ')'


                / Factor (MulOp Factor)*



then its canonical serialization (except for whitespace) is






    {/ {x {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}











This document, and the package it describes, will undoubtedly
    contain bugs and other problems. Please report such in the category
    pt of the Tcllib SF Trackers
    [http://sourceforge.net/tracker/?group_id=12883]. Please also report any
    ideas for enhancements you may have for either package and/or
  documentation.








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








Parsing and Grammars








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








  

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