pt::pe(n) Parser Tools pt::pe(n) 







pt::pe - Parsing Expression Serialization








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












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









  
::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

  







  

  
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.










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