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>