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







pt::peg::export - PEG Export








package require Tcl 8.5


package require snit 


package require configuration 


package require pt::peg 


package require pluginmgr 


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


::pt::peg::export objectName


objectName method ?arg arg ...?


objectName destroy


objectName export serial serial
    ?format?


objectName export object object
    ?format?


objectName configuration names


objectName configuration get


objectName configuration set name
    ?value?


objectName configuration unset pattern...












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 manager for parsing expression grammars,
    with each instance handling a set of plugins for the export of them to other
    formats, i.e. their conversion to, for example nroff, HTML,
    etc.


It resides in the Export section of the Core Layer of Parser
    Tools, and is one of the three pillars the management of parsing expression
    grammars resides on.


IMAGE: arch_core_export


The other two pillars are, as shown above



  
[1]

  
PEG Import, and

  
[2]

  
PEG Storage




For information about the data structure which is the major input
    to the manager objects provided by this package see the section PEG
    serialization format.


The plugin system of this class is based on the package
    pluginmgr, and configured to look for plugins using



  
[1]

  
the environment variable GRAMMAR_PEG_EXPORT_PLUGINS,

  
[2]

  
the environment variable GRAMMAR_PEG_PLUGINS,

  
[3]

  
the environment variable GRAMMAR_PLUGINS,

  
[4]

  
the path "~/.grammar/peg/export/plugin"

  
[5]

  
the path "~/.grammar/peg/plugin"

  
[6]

  
the path "~/.grammar/plugin"

  
[7]

  
the path "~/.grammar/peg/export/plugins"

  
[8]

  
the path "~/.grammar/peg/plugins"

  
[9]

  
the path "~/.grammar/plugins"

  
[10]

  
the registry entry
      "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\EXPORT\PLUGINS"

  
[11]

  
the registry entry
      "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUGINS"

  
[12]

  
the registry entry
    "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PLUGINS"




The last three are used only when the package is run on a machine
    using the Windows(tm) operating system.


The whole system is delivered with three predefined export
    plugins, namely



  

  
See PEG Export Plugin. To CONTAINER format for details.

  

  
See PEG Export Plugin. To JSON format for details.

  

  
See PEG Export Plugin. To PEG format for details.




For readers wishing to write their own export plugin for some
    format, i.e. plugin writers, reading and understanding the Parser
    Tools Export API specification is an absolute necessity, as it documents
    the interaction between this package and its plugins in detail.













  
::pt::peg::export objectName

  
This command creates a new export manager object with an associated Tcl
      command whose name is objectName. This object command is
      explained in full detail in the sections Object command and
      Object methods. The object command will be created under the
      current namespace if the objectName is not fully qualified, and in
      the specified namespace otherwise.










All objects created by the ::pt::peg::export command have
    the following general form:



  

  
The method method and its arg'uments determine the exact
      behavior of the command. See section Object methods for the
      detailed specifications.











  

  
This method destroys the object it is invoked for.

  

  
This method takes the canonical serialization of a parsing expression
      grammar stored in serial and converts it to the specified
      format, using the export plugin for the format. This will fail with
      an error if no plugin could be found for the format. The string generated
      by the conversion process is returned as the result of this method.
    
If no format is specified the method defaults to
      text.

    
The specification of what a canonical serialization is
        can be found in the section PEG serialization format.

    
The plugin has to conform to the interface documented in the
        Parser Tools Export API specification.

  

  

  
This method is a convenient wrapper around the export serial method
      described by the previous item. It expects that object is an object
      command supporting a serialize method returning the canonical
      serialization of a parsing expression grammar. It invokes that method,
      feeds the result into export serial and returns the resulting
      string as its own result.

  

  
This method returns a list containing the names of all configuration
      options currently known to the object.

  

  
This method returns a dictionary containing the names and values of all
      configuration options currently known to the object.

  

  
This method sets the configuration option name to the specified
      value and returns the new value of the option.
    
If no value is specified it simply returns the current value,
        without changing it.

    
Note that these configuration options and their values are
        simply passed to a plugin when the actual export is performed. It is the
        plugin which checks the validity, not the manager.

  

  

  
This method unsets all configuration options matching the specified glob
      patterns. If no pattern is specified it will unset all currently
      defined configuration options.












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.








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








Parsing and Grammars








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








  

    1
    pt