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 <- '(' Expression ')' / (Factor (MulOp Factor)*)	;


    MulOp      <- '*' / '/'					;


    Factor     <- Term (AddOp Term)*				;


    AddOp      <- '+'/'-'					;


    Term       <- 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 <- '(' 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}
}

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 <- '(' 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}}}}}

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

COPYRIGHT

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