Provided by: tcllib_1.19-dfsg-2_all 
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 grammars, 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 expression 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. Otherwise 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 specified 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 container, 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 container, 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 container's method serialize to obtain the serialization of the table 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 assignment 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 grammar, 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 serialization 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 expression 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 nonterminal symbols known
to the grammar to their semantic modes.
objectName modes dict
This method takes a dictionary mapping a set of nonterminal symbols 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 nonterminal 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 symbols 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 symbols 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 specified in the section PE serialization format.
objectName add ?nt...?
This method adds the nonterminal symbols nt, etc. to the grammar, 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 nonterminal 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 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 symbol.
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 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).
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 symbol.
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 symbol, or pe does not contain a valid parsing
expression as specified in the section PE serialization format.
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.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can
be made by going to the Edit form of the ticket immediately after its creation, and then
using the left-most button in the secondary navigation bar.
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>