plucky (3) pt_peg_container.3tcl.gz
NAME
pt::peg::container - PEG Storage
SYNOPSIS
package require Tcl 8.5 9
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>