pt::peg::to::param(n) Parser Tools pt::peg::to::param(n)______________________________________________________________________________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 config‐
uration of the package.
pt::peg::to::param configure option
This command returns the current value of the specified configu‐
ration 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 pack‐
age, 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 com‐
mand.
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 vari‐
able -user.
@format@
To be replaced with the the constant PARAM.
@file@ To be replaced with the value of the configuration vari‐
able -file.
@name@ To be replaced with the value of the configuration vari‐
able -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 con‐
version is run. The default value is unknown.
PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS
The PARAM code representation of parsing expression grammars is assem‐
bler-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 inci‐
dentials of a framework, i.e. like the supporting C and Tcl code gener‐
ated 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 Pars‐
ing 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 expres‐
sion. 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 dictio‐
nary 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 serial‐
ization format.
mode The value can be one of three values
specifying how a parser should han‐
dle the semantic value produced by
the symbol.
value The semantic value of the
nonterminal symbol is an
abstract syntax tree consist‐
ing of a single node node for
the nonterminal itself, which
has the ASTs of the symbol's
right hand side as its chil‐
dren.
leaf The semantic value of the
nonterminal symbol is an
abstract syntax tree consist‐
ing 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 seman‐
tic value. Any ASTs generated
by the symbol's right hand
side are discarded (as well).
start The value is the serialization of the start pars‐
ing expression of the grammar, as specified in the
section PE serialization format.
[4] The terminal symbols of the grammar are specified implic‐
itly 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 spec‐
ified 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 con‐
tain 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 Pars‐
ing 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 expres‐
sion. 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 charac‐
ter. 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 expres‐
sion. 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 charac‐
ter. 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, includ‐
ing 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 charac‐
ter. This is a custom extension of PEs based on
Tcl's builtin command string is.
[14] The string wordchar is an atomic parsing expres‐
sion. It matches any Unicode word character. This
is any alphanumeric character (see alnum), and any
connector punctuation characters (e.g. under‐
score). 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 repeti‐
tions.
[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 for‐
mat 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 con‐
tain 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
CATEGORY
Parsing and Grammars
COPYRIGHT
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
pt 1 pt::peg::to::param(n)
