pt_export_api(i) Parser Tools pt_export_api(i) 







pt_export_api - Parser Tools Export API








package require Tcl 8.5


CONVERTER reset


CONVERTER configure


CONVERTER configure option


CONVERTER configure option
  value...


CONVERTER convert serial


::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 document describes two APIs. First the API shared by all
    packages for the conversion of Parsing Expression Grammars into some other
    format, and then the API shared by the packages which implement the export
    plugins sitting on top of the conversion packages.


Its intended audience are people who wish to create their own
    converter for some type of output, and/or an export plugin for their or some
    other converter.


It resides in the Export section of the Core Layer of Parser
    Tools.


IMAGE: arch_core_export








Any (grammar) export converter has to follow the rules set out
    below:



  
[1]

  
A converter is a package. Its name is arbitrary, however it is recommended
      to put it under the ::pt::peg::to namespace.

  
[2]

  
The package provides either a single Tcl command following the API
      outlined below, or a class command whose instances follow the same API.
      The commands which follow the API are called converter
    commands.

  
[3]

  
A converter command has to provide the following three methods with the
      given signatures and semantics. Converter commands are allowed to provide
      more methods of their own, but not less, and they may not provide
      different semantics for the standardized methods.







  

  
This method has to reset the configuration of the converter to its default
      settings. The result of the method has to be the empty string.

  

  
This method, in this form, has to return a dictionary containing the
      current configuration of the converter.

  

  
This method, in this form, has to return the current value of the
      specified configuration option of the converter.
    
Please read the section Options for the set of standard
        options any converter has to accept. Any other options accepted by a
        specific converter will be described in its manpage.

  

  

  
This command, in this form, sets the specified options of the
      converter to the given values.
    
Please read the section Options for the set of standard
        options a converter has to accept. Any other options accepted by a
        specific converter will be described in its manpage.

  

  

  
This method has to accept the canonical serialization of a parsing
      expression grammar, as specified in section PEG serialization
      format, and contained in serial. The result of the method has
      to be the result of converting the input grammar into whatever the
      converter is for, per its configuration.












Any (grammar) export plugin has to follow the rules set out
  below:



  
[1]

  
A plugin is a package.

  
[2]

  
The name of a plugin package has the form pt::peg::export::FOO,
      where FOO is the name of the format the plugin will generate output
      for.

  
[3]

  
The plugin can expect that the package pt::peg::export::plugin is
      present, as indicator that it was invoked from a genuine plugin manager.
    
It is recommended that a plugin does check for the presence of
        this package.

  

  
[4]

  
A plugin has to provide a single command, in the global namespace, with
      the signature shown below. Plugins are allowed to provide more command of
      their own, but not less, and they may not provide different semantics for
      the standardized command.







  
::export serial configuration

  
This command has to accept the canonical serialization of a parsing
      expression grammar and the configuration for the converter invoked by the
      plugin. The result of the command has to be the result of the converter
      invoked by the plugin for th input grammar and configuration.







  

  
This argument will contain the canonical serialization of the
      parsing expression grammar for which to generate the output. The
      specification of what a canonical serialization is can be found in
      the section PEG serialization format.

  

  
This argument will contain the configuration to configure the converter
      with before invoking it, as a dictionary mapping from options to values.
    
Please read the section Options for the set of standard
        options any converter has to accept, and thus any plugin as well. Any
        other options accepted by a specific plugin will be described in its
        manpage.

  









  
[5]

  
A single usage cycle of a plugin consists of an invokation of the command
      export. This call has to leave the plugin in a state where another
      usage cycle can be run without problems.










Each export converter and plugin for an export converter has to
    accept the options below in their configure method. Converters are
    allowed to ignore the contents of these options when performing a
    conversion, but they must not reject them. Plugins are expected to pass the
    options given to them to the converter they are invoking.



  

  
The value of this option is the name of the file or other entity from
      which the grammar came, for which the command is run. The default value is
      unknown.

  

  
The value of this option is the name of the grammar we are processing. The
      default value is a_pe_grammar.

  

  
The value of this option is the name of the user for which the command is
      run. The default value is unknown.










To use a converter do


    # Get the converter (single command here, not class)
    package require the-converter-package
    # Provide a configuration
    theconverter configure ...
    # Perform the conversion
    set result [theconverter convert $thegrammarserial]
    ... process the result ...



To use a plugin FOO do


    # Get an export plugin manager
    package require pt::peg::export
    pt::peg::export E
    # Provide a configuration
    E configuration set ...
    # Run the plugin, and the converter inside.
    set result [E export serial $grammarserial FOO]
    ... process the result ...









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>








  

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