Provided by: tcllib_1.17-dfsg-1_all 
NAME
pt::peg::export::container - PEG Export Plugin. Write CONTAINER format
SYNOPSIS
package require Tcl 8.5
package require pt::peg::export::container ?1?
package require pt::peg::to::container
export serial configuration
_________________________________________________________________________________________________
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 parsing expression grammar export plugin for the generation of
CONTAINER markup.
It resides in the Export section of the Core Layer of Parser Tools and is intended to be
used by pt::peg::export, the export manager, sitting between it and the corresponding core
conversion functionality provided by pt::peg::to::container.
IMAGE: arch_core_eplugins
While the direct use of this package with a regular interpreter is possible, this is
strongly disrecommended and requires a number of contortions to provide the expected
environment. The proper way to use this functionality depends on the situation:
[1] In an untrusted environment the proper access is through the package
pt::peg::export and the export manager objects it provides.
[2] In a trusted environment however simply use the package pt::peg::to::container and
access the core conversion functionality directly.
API
The API provided by this package satisfies the specification of the Plugin API found in
the Parser Tools Export API specification.
export serial configuration
This command takes the canonical serialization of a parsing expression grammar, as
specified in section PEG serialization format, and contained in serial, the
configuration, a dictionary, and generates CONTAINER markup encoding the grammar.
The created string is then returned as the result of the command.
CONFIGURATION
The CONTAINER export plugin recognizes the following configuration variables and changes
its behaviour as they specify.
enum mode
The value of this configuration variable controls which methods of pt::peg
instances the plugin will use to specify the grammar. There are two legal values
bulk In this mode the methods start, add, modes, and rules are used to specify
the grammar in a bulk manner, i.e. as a set of nonterminal symbols, and two
dictionaries mapping from the symbols to their semantic modes and parsing
expressions.
This mode is the default.
incremental
In this mode the methods start, add, mode, and rule are used to specify the
grammar piecemal, with each nonterminal having its own block of defining
commands.
string template
If this configuration variable is set it is assumed to contain a string into which
to put the generated code and other configuration data. The various locations are
expected to be specified with the following placeholders:
@user@ To be replaced with the value of the configuration variable user.
@format@
To be replaced with the the constant CONTAINER.
@file@ To be replaced with the value of the configuration variable file.
@name@ To be replaced with the value of the configuration variable name.
@mode@ To be replaced with the value of the configuration variable mode.
@code@ To be replaced with the generated code.
If this configuration variable is not set, or empty, then the plugin falls back to a
standard template, which is defined as "@code@".
Note that this plugin may ignore the standard configuration variables user, format, file,
and their values, depending on the chosen template.
The content of the standard configuration variable name, if set, is used as name of the
grammar in the output. Otherwise the plugin falls back to the default name a_pe_grammar.
GRAMMAR CONTAINER
The container format is another form of describing parsing expression grammars. While data
in this format is executable it does not constitute a parser for the grammar. It always
has to be used in conjunction with the package pt::peg::interp, a grammar interpreter.
The format represents grammars by a snit::type, i.e. class, whose instances are API-
compatible to the instances of the pt::peg::container package, and which are preloaded
with the grammar in question.
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 CONTAINER serialization for it is
snit::type a_pe_grammar {
constructor {} {
install myg using pt::peg::container ${selfns}::G
$myg start {n Expression}
$myg add AddOp Digit Expression Factor MulOp Number Sign Term
$myg modes {
AddOp value
Digit value
Expression value
Factor value
MulOp value
Number value
Sign value
Term value
}
$myg rules {
AddOp {/ {t -} {t +}}
Digit {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}
Expression {/ {x {t \50} {n Expression} {t \51}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}
Factor {x {n Term} {* {x {n AddOp} {n Term}}}}
MulOp {/ {t *} {t /}}
Number {x {? {n Sign}} {+ {n Digit}}}
Sign {/ {t -} {t +}}
Term {n Number}
}
return
}
component myg
delegate method * to myg
}
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 Trackers
[http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you
may have for either package and/or documentation.
KEYWORDS
CONTAINER, EBNF, LL(k), PEG, TDPL, context-free languages, export, expression, grammar,
matching, parser, parsing expression, parsing expression grammar, plugin, 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>