pt::peg::container(n) Parser Tools pt::peg::container(n)______________________________________________________________________________NAME
pt::peg::container - PEG Storage
SYNOPSIS
package require Tcl 8.5
package require snit
package require pt::peg::container ?1?
::pt::peg objectName ?=|:=|<--|as|deserialize src?
objectName destroy
objectName clear
objectName importer
objectName importer object
objectName exporter
objectName exporter object
objectName = source
objectName --> destination
objectName serialize ?format?
objectName deserialize = data ?format?
objectName deserialize += data ?format?
objectName start
objectName start pe
objectName nonterminals
objectName modes
objectName modes dict
objectName rules
objectName rules dict
objectName add ?nt...?
objectName remove ?nt...?
objectName exists nt
objectName rename ntold ntnew
objectName mode nt
objectName mode nt mode
objectName rule nt
objectName rule nt pe
_________________________________________________________________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 provides a container class for parsing expression gram‐
mars, with each instance storing a single grammar and allowing the user
to manipulate and query its definition.
It resides in the Storage section of the Core Layer of Parser Tools,
and is one of the three pillars the management of parsing expression
grammars resides on.
IMAGE: arch_core_container
The other two pillars are, as shown above
[1] PEG Import, and
[2] PEG Export
Packages related to this are:
pt::rde
This package provides an implementation of PARAM, a virtual
machine for the parsing of a channel, geared towards the needs
of handling PEGs.
pt::peg::interp
This package implements an interpreter for PEGs on top of the
virtual machine provided by pt::peg::rde
CLASS API
The package exports the API described here.
::pt::peg objectName ?=|:=|<--|as|deserialize src?
The command creates a new container object for a parsing expres‐
sion grammar and returns the fully qualified name of the object
command as its result. The API of this object command is
described in the section Object API. It may be used to invoke
various operations on the object.
The new container will be empty if no src is specified. Other‐
wise it will contain a copy of the grammar contained in the src.
All operators except deserialize interpret src as a container
object command. The deserialize operator interprets src as the
serialization of a parsing expression grammar instead, as speci‐
fied in section PEG serialization format.
An empty grammar has no nonterminal symbols, and the start
expression is the empty expression, i.e. epsilon. It is valid,
but not useful.
OBJECT API
All objects created by this package provide the following methods for
the manipulation and querying of their contents:
objectName destroy
This method destroys the object, releasing all claimed memory,
and deleting the associated object command.
objectName clear
This method resets the object to contain the empty grammar. It
does not destroy the object itself.
objectName importer
This method returns the import manager object currently attached
to the container, if any.
objectName importer object
This method attaches the object as import manager to the con‐
tainer, and returns it as the result of the command. Note that
the object is not put into ownership of the container. I.e.,
destruction of the container will not destroy the object.
It is expected that object provides a method named import text
which takes a text and a format name, and returns the canonical
serialization of the table of contents contained in the text,
assuming the given format.
objectName exporter
This method returns the export manager object currently attached
to the container, if any.
objectName exporter object
This method attaches the object as export manager to the con‐
tainer, and returns it as the result of the command. Note that
the object is not put into ownership of the container. I.e.,
destruction of the container will not destroy the object.
It is expected that object provides a method named export object
which takes the container and a format name, and returns a text
encoding table of contents stored in the container, in the given
format. It is further expected that the object will use the con‐
tainer's method serialize to obtain the serialization of the ta‐
ble of contents from which to generate the text.
objectName = source
This method assigns the contents of the PEG object source to
ourselves, overwriting the existing definition. This is the
assignment operator for grammars.
This operation is in effect equivalent to
objectName deserialize = [source serialize]
objectName --> destination
This method assigns our contents to the PEG object destination,
overwriting the existing definition. This is the reverse assign‐
ment operator for grammars.
This operation is in effect equivalent to
destination deserialize = [objectName serialize]
objectName serialize ?format?
This method returns our grammar in some textual form usable for
transfer, persistent storage, etc. If no format is not specified
the returned result is the canonical serialization of the gram‐
mar, as specified in the section PEG serialization format.
Otherwise the object will use the attached export manager to
convert the data to the specified format. In that case the
method will fail with an error if the container has no export
manager attached to it.
objectName deserialize = data ?format?
This is the complementary method to serialize. It replaces the
current definition with the grammar contained in the data. If no
format was specified it is assumed to be the regular serializa‐
tion of a grammar, as specified in the section PEG serialization
format
Otherwise the object will use the attached import manager to
convert the data from the specified format to a serialization it
can handle. In that case the method will fail with an error if
the container has no import manager attached to it.
The result of the method is the empty string.
objectName deserialize += data ?format?
This method behaves like deserialize = in its essentials, except
that it merges the grammar in the data to its contents instead
of replacing it. The method will fail with an error and leave
the grammar unchanged if merging is not possible, i.e. would
produce an invalid grammar.
The result of the method is the empty string.
objectName start
This method returns the current start expression of the grammar.
objectName start pe
This method defines the start expression of the grammar. It
replaces the current start expression with the parsing expres‐
sion pe, and returns the new start expression.
The method will fail with an error and leave the grammar
unchanged if pe does not contain a valid parsing expression as
specified in the section PE serialization format.
objectName nonterminals
This method returns the set of all nonterminal symbols known to
the grammar.
objectName modes
This method returns a dictionary mapping the set of all nonter‐
minal symbols known to the grammar to their semantic modes.
objectName modes dict
This method takes a dictionary mapping a set of nonterminal sym‐
bols known to the grammar to their semantic modes, and returns
the new full mapping of nonterminal symbols to semantic modes.
The method will fail with an error if any of the nonterminal
symbols in the dictionary is not known to the grammar, or the
empty string, i.e. an invalid nonterminal symbol, or if any the
chosen modes is not one of the legal values.
objectName rules
This method returns a dictionary mapping the set of all nonter‐
minal symbols known to the grammar to their parsing expressions
(right-hand sides).
objectName rules dict
This method takes a dictionary mapping a set of nonterminal sym‐
bols known to the grammar to their parsing expressions (right-
hand sides), and returns the new full mapping of nonterminal
symbols to parsing expressions.
The method will fail with an error any of the nonterminal sym‐
bols in the dictionary is not known to the grammar, or the empty
string, i.e. an invalid nonterminal symbol, or any of the chosen
parsing expressions is not a valid parsing expression as speci‐
fied in the section PE serialization format.
objectName add ?nt...?
This method adds the nonterminal symbols nt, etc. to the gram‐
mar, and defines default semantic mode and expression for it
(value and epsilon respectively). The method returns the empty
string as its result.
The method will fail with an error and leaves the grammar
unchanged if any of the nonterminal symbols are either already
defined in our grammar, or are the empty string (an invalid non‐
terminal symbol).
The method does nothing if no symbol was specified as argument.
objectName remove ?nt...?
This method removes the named nonterminal symbols nt, etc. from
the set of nonterminal symbols known to our grammar. The method
returns the empty string as its result.
The method will fail with an error and leave the grammar
unchanged if any of the nonterminal symbols is not known to the
grammar, or is the empty string, i.e. an invalid nonterminal
symbol.
objectName exists nt
This method tests whether the nonterminal symbol nt is known to
our grammar or not. The result is a boolean value. It will be
set to true if nt is known, and false otherwise.
The method will fail with an error if nt is the empty string,
i.e. an invalid nonterminal symbol.
objectName rename ntold ntnew
This method renames the nonterminal symbol ntold to ntnew. The
method returns the empty string as its result.
The method will fail with an error and leave the grammar
unchanged if either ntold is not known to the grammar, or ntnew
is already known, or any of them is the empty string, i.e. an
invalid nonterminal symbol.
objectName mode nt
This method returns the current semantic mode for the nontermi‐
nal symbol nt.
The method will fail with an error if nt is not known to the
grammar, or the empty string, i.e. an invalid nonterminal sym‐
bol.
objectName mode nt mode
This mode sets the semantic mode for the nonterminal symbol nt,
and returns the new mode. The method will fail with an error if
nt is not known to the grammar, or the empty string, i.e. an
invalid nonterminal symbol, or the chosen mode is not one of the
legal values.
The following modes are legal:
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 sym‐
bol'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).
objectName rule nt
This method returns the current parsing expression (right-hand
side) for the nonterminal symbol nt.
The method will fail with an error if nt is not known to the
grammar, or the empty string, i.e. an invalid nonterminal sym‐
bol.
objectName rule nt pe
This method set the parsing expression (right-hand side) of the
nonterminal nt to pe, and returns the new parsing expression.
The method will fail with an error if nt is not known to the
grammar, or the empty string, i.e. an invalid nonterminal sym‐
bol, or pe does not contain a valid parsing expression as speci‐
fied in the section PE serialization format.
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), PEG, TDPL, context-free languages, expression, grammar,
matching, parser, parsing expression, parsing expression grammar, push
down automaton, recursive descent, 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::container(n)
