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pt::pe(3tcl) Parser Tools pt::pe(3tcl) 


NAME

pt::pe - Parsing Expression Serialization

SYNOPSIS

package require Tcl 8.5

 

package require pt::pe ?1?

 

package require char 

 

::pt::pe verify serial ?canonvar?

 

::pt::pe verify-as-canonical serial

 

::pt::pe canonicalize serial

 

::pt::pe print serial

 

::pt::pe bottomup cmdprefix pe

 

cmdprefix pe op arguments

 

::pt::pe topdown cmdprefix pe

 

::pt::pe equal seriala serialb

 

::pt::pe epsilon

 

::pt::pe dot

 

::pt::pe alnum

 

::pt::pe alpha

 

::pt::pe ascii

 

::pt::pe control

 

::pt::pe digit

 

::pt::pe graph

 

::pt::pe lower

 

::pt::pe print

 

::pt::pe punct

 

::pt::pe space

 

::pt::pe upper

 

::pt::pe wordchar

 

::pt::pe xdigit

 

::pt::pe ddigit

 

::pt::pe terminal t

 

::pt::pe range ta tb

 

::pt::pe nonterminal nt

 

::pt::pe choice pe...

 

::pt::pe sequence pe...

 

::pt::pe repeat0 pe

 

::pt::pe repeat1 pe

 

::pt::pe optional pe

 

::pt::pe ahead pe

 

::pt::pe notahead pe

 




 


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 commands to work with the serializations of parsing
  expressions as managed by the Parser Tools, and specified in section PE
  serialization format.


This is a supporting package in the Core Layer of Parser Tools.


IMAGE: arch_core_support

API



  
::pt::pe verify serial
    ?canonvar?

  
This command verifies that the content of serial is
      a valid serialization of a parsing expression and will throw an error if
      that is not the case. The result of the command is the empty string.
    
 

    If the argument canonvar is specified it is interpreted as the name
      of a variable in the calling context. This variable will be written to if
      and only if serial is a valid regular serialization. Its value will
      be a boolean, with True indicating that the serialization is not
      only valid, but also canonical. False will be written for a
      valid, but non-canonical serialization.
    
 

    For the specification of serializations see the section PE serialization
      format.





  
::pt::pe verify-as-canonical
    serial

  
This command verifies that the content of serial is
      a valid canonical serialization of a parsing expression and will
      throw an error if that is not the case. The result of the command is the
      empty string.
    
 

    For the specification of canonical serializations see the section PE
      serialization format.





  
::pt::pe canonicalize serial

  
This command assumes that the content of serial is a
      valid regular serialization of a parsing expression and will throw
      an error if that is not the case.
    
 

    It will then convert the input into the canonical serialization of
      this parsing expression and return it as its result. If the input is
      already canonical it will be returned unchanged.
    
 

    For the specification of regular and canonical serializations see the
      section PE serialization format.





  
::pt::pe print serial

  
This command assumes that the argument serial
      contains a valid serialization of a parsing expression and returns a
      string containing that PE in a human readable form.
    
 

    The exact format of this form is not specified and cannot be relied on for
      parsing or other machine-based activities.
    
 

    For the specification of serializations see the section PE serialization
      format.





  
::pt::pe bottomup cmdprefix
    pe

  
This command walks the parsing expression pe from
      the bottom up to the root, invoking the command prefix cmdprefix
      for each partial expression. This implies that the children of a parsing
      expression PE are handled before PE.
    
 

    The command prefix has the signature







  
cmdprefix pe op arguments

  
I.e. it is invoked with the parsing expression pe
      the walk is currently at, the op'erator in the pe, and the
      operator's arguments.
    
 

    The result returned by the command prefix replaces pe in the parsing
      expression it was a child of, allowing transformations of the expression
      tree.
    
 

    This also means that for all inner parsing expressions the contents of
      arguments are the results of the command prefix invoked for the
      children of this inner parsing expression.







  
::pt::pe topdown cmdprefix
    pe

  
This command walks the parsing expression pe from
      the root down to the leaves, invoking the command prefix cmdprefix
      for each partial expression. This implies that the children of a parsing
      expression PE are handled after PE.
    
 

    The command prefix has the same signature as for bottomup, see above.
    
 

    The result returned by the command prefix is ignored.





  
::pt::pe equal seriala
    serialb

  
This command tests the two parsing expressions
      seriala and serialb for structural equality. The result of
      the command is a boolean value. It will be set to true if the
      expressions are identical, and false otherwise.
    
 

    String equality is usable only if we can assume that the two parsing
      expressions are pure Tcl lists.





  
::pt::pe epsilon

  
This command constructs the atomic parsing expression for
      epsilon.





  
::pt::pe dot

  
This command constructs the atomic parsing expression for
      dot.





  
::pt::pe alnum

  
This command constructs the atomic parsing expression for
      alnum.





  
::pt::pe alpha

  
This command constructs the atomic parsing expression for
      alpha.





  
::pt::pe ascii

  
This command constructs the atomic parsing expression for
      ascii.





  
::pt::pe control

  
This command constructs the atomic parsing expression for
      control.





  
::pt::pe digit

  
This command constructs the atomic parsing expression for
      digit.





  
::pt::pe graph

  
This command constructs the atomic parsing expression for
      graph.





  
::pt::pe lower

  
This command constructs the atomic parsing expression for
      lower.





  
::pt::pe print

  
This command constructs the atomic parsing expression for
      print.





  
::pt::pe punct

  
This command constructs the atomic parsing expression for
      punct.





  
::pt::pe space

  
This command constructs the atomic parsing expression for
      space.





  
::pt::pe upper

  
This command constructs the atomic parsing expression for
      upper.





  
::pt::pe wordchar

  
This command constructs the atomic parsing expression for
      wordchar.





  
::pt::pe xdigit

  
This command constructs the atomic parsing expression for
      xdigit.





  
::pt::pe ddigit

  
This command constructs the atomic parsing expression for
      ddigit.





  
::pt::pe terminal t

  
This command constructs the atomic parsing expression for
      the terminal symbol t.





  
::pt::pe range ta tb

  
This command constructs the atomic parsing expression for
      the range of terminal symbols ta ... tb.





  
::pt::pe nonterminal nt

  
This command constructs the atomic parsing expression for
      the nonterminal symbol nt.





  
::pt::pe choice pe...

  
This command constructs the parsing expression representing
      the ordered or prioritized choice between the argument parsing
      expressions. The first argument has the highest priority.





  
::pt::pe sequence pe...

  
This command constructs the parsing expression representing
      the sequence of the argument parsing expression. The first argument is the
      first element of the sequence.





  
::pt::pe repeat0 pe

  
This command constructs the parsing expression representing
      the zero or more repetition of the argument parsing expression pe,
      also known as the kleene closure.





  
::pt::pe repeat1 pe

  
This command constructs the parsing expression representing
      the one or more repetition of the argument parsing expression pe,
      also known as the positive kleene closure.





  
::pt::pe optional pe

  
This command constructs the parsing expression representing
      the optionality of the argument parsing expression pe.





  
::pt::pe ahead pe

  
This command constructs the parsing expression representing
      the positive lookahead of the argument parsing expression pe.





  
::pt::pe notahead pe

  
This command constructs the parsing expression representing
      the negative lookahead of the argument parsing expression pe.




PE SERIALIZATION FORMAT

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.


  
Regular serialization

  







  
Atomic Parsing Expressions

  







  
[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.







  
Combined Parsing Expressions

  







  
[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.









  
Canonical serialization

  
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).






EXAMPLE

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








    Expression <- Term (AddOp Term)*








then its canonical serialization (except for whitespace) is








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







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
  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.

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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