Provided by: tcllib_1.14-dfsg-1_all bug

NAME

       pt::peg::to::param - PEG Conversion. Write PARAM format

SYNOPSIS

       package require Tcl  8.5

       package require pt::peg::to::param  ?1?

       package require pt::peg

       package require pt::pe

       pt::peg::to::param reset

       pt::peg::to::param configure

       pt::peg::to::param configure option

       pt::peg::to::param configure option value...

       pt::peg::to::param convert serial

_________________________________________________________________

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 implements the converter from parsing expression grammars to PARAM markup.

       It resides in the Export section of the Core Layer of Parser Tools, and can be used either
       directly with the other packages of this layer, or indirectly through the  export  manager
       provided  by pt::peg::export. The latter is intented for use in untrusted environments and
       done through  the  corresponding  export  plugin  pt::peg::export::param  sitting  between
       converter and export manager.

       IMAGE: arch_core_eplugins

API

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

       pt::peg::to::param reset
              This command resets the configuration of the package to its default settings.

       pt::peg::to::param configure
              This command returns a dictionary  containing  the  current  configuration  of  the
              package.

       pt::peg::to::param configure option
              This command returns the current value of the specified configuration option of the
              package. For the set of legal options, please read the section Options.

       pt::peg::to::param configure option value...
              This command sets the given configuration options of the package, to the  specified
              values. For the set of legal options, please read the section Options.

       pt::peg::to::param convert serial
              This  command takes the canonical serialization of a parsing expression grammar, as
              specified in section  PEG  serialization  format,  and  contained  in  serial,  and
              generates PARAM markup encoding the grammar, per the current package configuration.
              The created string is then returned as the result of the command.

OPTIONS

       The converter to PARAM markup recognizes the following configuration variables and changes
       its behaviour as they specify.

       -template string
              The  value  of  this  configuration  variable  is  a  string  into which to put the
              generated text and the other configuration  settings.  The  various  locations  for
              user-data  are  expected  to  be  specified with the placeholders listed below. The
              default value is "@code@".

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

              @format@
                     To be replaced with the the constant PARAM.

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

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

              @code@ To be replaced with the generated text.

       -name string
              The value of this configuration variable is the name of the grammar for  which  the
              conversion is run. The default value is a_pe_grammar.

       -user string
              The  value  of  this  configuration  variable is the name of the user for which the
              conversion is run. The default value is unknown.

       -file string
              The value of this configuration variable is the name of the file  or  other  entity
              from  which the grammar came, for which the conversion is run. The default value is
              unknown.

PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS

       The PARAM code representation of parsing expression grammars is assembler-like text  using
       the  instructions  of the virtual machine documented in the PackRat Machine Specification,
       plus a few more for control flow (jump ok, jump fail, call symbol, return).

       It is not really useful, except possibly as a tool demonstrating how a grammar is compiled
       in  general,  without getting distracted by the incidentials of a framework, i.e. like the
       supporting C and Tcl code generated by the other PARAM-derived formats.

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

   EXAMPLE
       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 <- Term (AddOp Term)*                            ;
                  MulOp      <- '*' / '/'                                     ;
                  Term       <- Factor (MulOp Factor)*                        ;
                  AddOp      <- '+'/'-'                                       ;
                  Factor     <- '(' Expression ')' / Number                   ;
              END;

       one possible PARAM serialization for it is

              # -*- text -*-
              # Parsing Expression Grammar 'TEMPLATE'.
              # Generated for unknown, from file 'TEST'

              #
              # Grammar Start Expression
              #

              <<MAIN>>:
                       call              sym_Expression
                       halt

              #
              # value Symbol 'AddOp'
              #

              sym_AddOp:
              # /
              #     '-'
              #     '+'

                       symbol_restore    AddOp
                found! jump              found_7
                       loc_push

                       call              choice_5

                 fail! value_clear
                   ok! value_leaf        AddOp
                       symbol_save       AddOp
                       error_nonterminal AddOp
                       loc_pop_discard

              found_7:
                   ok! ast_value_push
                       return

              choice_5:
              # /
              #     '-'
              #     '+'

                       error_clear

                       loc_push
                       error_push

                       input_next        "t -"
                   ok! test_char         "-"

                       error_pop_merge
                   ok! jump              oknoast_4

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t +"
                   ok! test_char         "+"

                       error_pop_merge
                   ok! jump              oknoast_4

                       loc_pop_rewind
                       status_fail
                       return

              oknoast_4:
                       loc_pop_discard
                       return
              #
              # value Symbol 'Digit'
              #

              sym_Digit:
              # /
              #     '0'
              #     '1'
              #     '2'
              #     '3'
              #     '4'
              #     '5'
              #     '6'
              #     '7'
              #     '8'
              #     '9'

                       symbol_restore    Digit
                found! jump              found_22
                       loc_push

                       call              choice_20

                 fail! value_clear
                   ok! value_leaf        Digit
                       symbol_save       Digit
                       error_nonterminal Digit
                       loc_pop_discard

              found_22:
                   ok! ast_value_push
                       return

              choice_20:
              # /
              #     '0'
              #     '1'
              #     '2'
              #     '3'
              #     '4'
              #     '5'
              #     '6'
              #     '7'
              #     '8'
              #     '9'

                       error_clear

                       loc_push
                       error_push

                       input_next        "t 0"
                   ok! test_char         "0"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 1"
                   ok! test_char         "1"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 2"
                   ok! test_char         "2"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 3"
                   ok! test_char         "3"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 4"
                   ok! test_char         "4"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 5"
                   ok! test_char         "5"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 6"
                   ok! test_char         "6"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 7"
                   ok! test_char         "7"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 8"
                   ok! test_char         "8"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t 9"
                   ok! test_char         "9"

                       error_pop_merge
                   ok! jump              oknoast_19

                       loc_pop_rewind
                       status_fail
                       return

              oknoast_19:
                       loc_pop_discard
                       return
              #
              # value Symbol 'Expression'
              #

              sym_Expression:
              # /
              #     x
              #         '\('
              #         (Expression)
              #         '\)'
              #     x
              #         (Factor)
              #         *
              #             x
              #                 (MulOp)
              #                 (Factor)

                       symbol_restore    Expression
                found! jump              found_46
                       loc_push
                       ast_push

                       call              choice_44

                 fail! value_clear
                   ok! value_reduce      Expression
                       symbol_save       Expression
                       error_nonterminal Expression
                       ast_pop_rewind
                       loc_pop_discard

              found_46:
                   ok! ast_value_push
                       return

              choice_44:
              # /
              #     x
              #         '\('
              #         (Expression)
              #         '\)'
              #     x
              #         (Factor)
              #         *
              #             x
              #                 (MulOp)
              #                 (Factor)

                       error_clear

                       ast_push
                       loc_push
                       error_push

                       call              sequence_27

                       error_pop_merge
                   ok! jump              ok_43

                       ast_pop_rewind
                       loc_pop_rewind
                       ast_push
                       loc_push
                       error_push

                       call              sequence_40

                       error_pop_merge
                   ok! jump              ok_43

                       ast_pop_rewind
                       loc_pop_rewind
                       status_fail
                       return

              ok_43:
                       ast_pop_discard
                       loc_pop_discard
                       return

              sequence_27:
              # x
              #     '\('
              #     (Expression)
              #     '\)'

                       loc_push
                       error_clear

                       error_push

                       input_next        "t ("
                   ok! test_char         "("

                       error_pop_merge
                 fail! jump              failednoast_29
                       ast_push
                       error_push

                       call              sym_Expression

                       error_pop_merge
                 fail! jump              failed_28
                       error_push

                       input_next        "t )"
                   ok! test_char         ")"

                       error_pop_merge
                 fail! jump              failed_28

                       ast_pop_discard
                       loc_pop_discard
                       return

              failed_28:
                       ast_pop_rewind

              failednoast_29:
                       loc_pop_rewind
                       return

              sequence_40:
              # x
              #     (Factor)
              #     *
              #         x
              #             (MulOp)
              #             (Factor)

                       ast_push
                       loc_push
                       error_clear

                       error_push

                       call              sym_Factor

                       error_pop_merge
                 fail! jump              failed_41
                       error_push

                       call              kleene_37

                       error_pop_merge
                 fail! jump              failed_41

                       ast_pop_discard
                       loc_pop_discard
                       return

              failed_41:
                       ast_pop_rewind
                       loc_pop_rewind
                       return

              kleene_37:
              # *
              #     x
              #         (MulOp)
              #         (Factor)

                       loc_push
                       error_push

                       call              sequence_34

                       error_pop_merge
                 fail! jump              failed_38
                       loc_pop_discard
                       jump              kleene_37

              failed_38:
                       loc_pop_rewind
                       status_ok
                       return

              sequence_34:
              # x
              #     (MulOp)
              #     (Factor)

                       ast_push
                       loc_push
                       error_clear

                       error_push

                       call              sym_MulOp

                       error_pop_merge
                 fail! jump              failed_35
                       error_push

                       call              sym_Factor

                       error_pop_merge
                 fail! jump              failed_35

                       ast_pop_discard
                       loc_pop_discard
                       return

              failed_35:
                       ast_pop_rewind
                       loc_pop_rewind
                       return
              #
              # value Symbol 'Factor'
              #

              sym_Factor:
              # x
              #     (Term)
              #     *
              #         x
              #             (AddOp)
              #             (Term)

                       symbol_restore    Factor
                found! jump              found_60
                       loc_push
                       ast_push

                       call              sequence_57

                 fail! value_clear
                   ok! value_reduce      Factor
                       symbol_save       Factor
                       error_nonterminal Factor
                       ast_pop_rewind
                       loc_pop_discard

              found_60:
                   ok! ast_value_push
                       return

              sequence_57:
              # x
              #     (Term)
              #     *
              #         x
              #             (AddOp)
              #             (Term)

                       ast_push
                       loc_push
                       error_clear

                       error_push

                       call              sym_Term

                       error_pop_merge
                 fail! jump              failed_58
                       error_push

                       call              kleene_54

                       error_pop_merge
                 fail! jump              failed_58

                       ast_pop_discard
                       loc_pop_discard
                       return

              failed_58:
                       ast_pop_rewind
                       loc_pop_rewind
                       return

              kleene_54:
              # *
              #     x
              #         (AddOp)
              #         (Term)

                       loc_push
                       error_push

                       call              sequence_51

                       error_pop_merge
                 fail! jump              failed_55
                       loc_pop_discard
                       jump              kleene_54

              failed_55:
                       loc_pop_rewind
                       status_ok
                       return

              sequence_51:
              # x
              #     (AddOp)
              #     (Term)

                       ast_push
                       loc_push
                       error_clear

                       error_push

                       call              sym_AddOp

                       error_pop_merge
                 fail! jump              failed_52
                       error_push

                       call              sym_Term

                       error_pop_merge
                 fail! jump              failed_52

                       ast_pop_discard
                       loc_pop_discard
                       return

              failed_52:
                       ast_pop_rewind
                       loc_pop_rewind
                       return
              #
              # value Symbol 'MulOp'
              #

              sym_MulOp:
              # /
              #     '*'
              #     '/'

                       symbol_restore    MulOp
                found! jump              found_67
                       loc_push

                       call              choice_65

                 fail! value_clear
                   ok! value_leaf        MulOp
                       symbol_save       MulOp
                       error_nonterminal MulOp
                       loc_pop_discard

              found_67:
                   ok! ast_value_push
                       return

              choice_65:
              # /
              #     '*'
              #     '/'

                       error_clear

                       loc_push
                       error_push

                       input_next        "t *"
                   ok! test_char         "*"

                       error_pop_merge
                   ok! jump              oknoast_64

                       loc_pop_rewind
                       loc_push
                       error_push

                       input_next        "t /"
                   ok! test_char         "/"

                       error_pop_merge
                   ok! jump              oknoast_64

                       loc_pop_rewind
                       status_fail
                       return

              oknoast_64:
                       loc_pop_discard
                       return
              #
              # value Symbol 'Number'
              #

              sym_Number:
              # x
              #     ?
              #         (Sign)
              #     +
              #         (Digit)

                       symbol_restore    Number
                found! jump              found_80
                       loc_push
                       ast_push

                       call              sequence_77

                 fail! value_clear
                   ok! value_reduce      Number
                       symbol_save       Number
                       error_nonterminal Number
                       ast_pop_rewind
                       loc_pop_discard

              found_80:
                   ok! ast_value_push
                       return

              sequence_77:
              # x
              #     ?
              #         (Sign)
              #     +
              #         (Digit)

                       ast_push
                       loc_push
                       error_clear

                       error_push

                       call              optional_70

                       error_pop_merge
                 fail! jump              failed_78
                       error_push

                       call              poskleene_73

                       error_pop_merge
                 fail! jump              failed_78

                       ast_pop_discard
                       loc_pop_discard
                       return

              failed_78:
                       ast_pop_rewind
                       loc_pop_rewind
                       return

              optional_70:
              # ?
              #     (Sign)

                       loc_push
                       error_push

                       call              sym_Sign

                       error_pop_merge
                 fail! loc_pop_rewind
                   ok! loc_pop_discard
                       status_ok
                       return

              poskleene_73:
              # +
              #     (Digit)

                       loc_push

                       call              sym_Digit

                 fail! jump              failed_74

              loop_75:
                       loc_pop_discard
                       loc_push
                       error_push

                       call              sym_Digit

                       error_pop_merge
                   ok! jump              loop_75
                       status_ok

              failed_74:
                       loc_pop_rewind
                       return
              #
              # value Symbol 'Sign'
              #

              sym_Sign:
              # /
              #     '-'
              #     '+'

                       symbol_restore    Sign
                found! jump              found_86
                       loc_push

                       call              choice_5

                 fail! value_clear
                   ok! value_leaf        Sign
                       symbol_save       Sign
                       error_nonterminal Sign
                       loc_pop_discard

              found_86:
                   ok! ast_value_push
                       return
              #
              # value Symbol 'Term'
              #

              sym_Term:
              # (Number)

                       symbol_restore    Term
                found! jump              found_89
                       loc_push
                       ast_push

                       call              sym_Number

                 fail! value_clear
                   ok! value_reduce      Term
                       symbol_save       Term
                       error_nonterminal Term
                       ast_pop_rewind
                       loc_pop_discard

              found_89:
                   ok! ast_value_push
                       return

              #
              #

PEG SERIALIZATION FORMAT

       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.

       regular serialization

              [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

                     rules  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

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

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

                                          value  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.

                                          leaf   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.

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

                     start  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.

       canonical serialization
              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.

   EXAMPLE
       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 <- Term (AddOp Term)*                            ;
                  MulOp      <- '*' / '/'                                     ;
                  Term       <- Factor (MulOp Factor)*                        ;
                  AddOp      <- '+'/'-'                                       ;
                  Factor     <- '(' Expression ')' / 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 {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
                      Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  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 {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}
                  }
                  start {n Expression}
              }

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),  PARAM,  PEG,  TDPL,  context-free languages, conversion, expression, format
       conversion, grammar, matching, parser, parsing  expression,  parsing  expression  grammar,
       push  down automaton, recursive descent, serialization, state, top-down parsing languages,
       transducer

CATEGORY

       Parsing and Grammars

COPYRIGHT

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