Provided by: tcllib_1.21+dfsg-1_all 
NAME
pt::peg::export - PEG Export
SYNOPSIS
package require Tcl 8.5
package require snit
package require struct::map
package require pt::peg
package require pluginmgr
package require pt::peg::export ?1.0.1?
::pt::peg::export objectName
objectName method ?arg arg ...?
objectName destroy
objectName export serial serial ?format?
objectName export object object ?format?
objectName configuration names
objectName configuration get
objectName configuration set name ?value?
objectName configuration unset pattern...
_________________________________________________________________________________________________
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 manager for parsing expression grammars, with each instance
handling a set of plugins for the export of them to other formats, i.e. their conversion
to, for example nroff, HTML, etc.
It resides in the Export 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_export
The other two pillars are, as shown above
[1] PEG Import, and
[2] PEG Storage
For information about the data structure which is the major input to the manager objects
provided by this package see the section PEG serialization format.
The plugin system of this class is based on the package pluginmgr, and configured to look
for plugins using
[1] the environment variable GRAMMAR_PEG_EXPORT_PLUGINS,
[2] the environment variable GRAMMAR_PEG_PLUGINS,
[3] the environment variable GRAMMAR_PLUGINS,
[4] the path "~/.grammar/peg/export/plugin"
[5] the path "~/.grammar/peg/plugin"
[6] the path "~/.grammar/plugin"
[7] the path "~/.grammar/peg/export/plugins"
[8] the path "~/.grammar/peg/plugins"
[9] the path "~/.grammar/plugins"
[10] the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\EXPORT\PLUGINS"
[11] the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUGINS"
[12] the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PLUGINS"
The last three are used only when the package is run on a machine using the Windows(tm)
operating system.
The whole system is delivered with three predefined export plugins, namely
container
See PEG Export Plugin. To CONTAINER format for details.
json See PEG Export Plugin. To JSON format for details.
peg See PEG Export Plugin. To PEG format for details.
For readers wishing to write their own export plugin for some format, i.e. plugin writers,
reading and understanding the Parser Tools Export API specification is an absolute
necessity, as it documents the interaction between this package and its plugins in detail.
API
PACKAGE COMMANDS
::pt::peg::export objectName
This command creates a new export manager object with an associated Tcl command
whose name is objectName. This object command is explained in full detail in the
sections Object command and Object methods. The object command will be created
under the current namespace if the objectName is not fully qualified, and in the
specified namespace otherwise.
OBJECT COMMAND
All objects created by the ::pt::peg::export command have the following general form:
objectName method ?arg arg ...?
The method method and its arg'uments determine the exact behavior of the command.
See section Object methods for the detailed specifications.
OBJECT METHODS
objectName destroy
This method destroys the object it is invoked for.
objectName export serial serial ?format?
This method takes the canonical serialization of a parsing expression grammar
stored in serial and converts it to the specified format, using the export plugin
for the format. This will fail with an error if no plugin could be found for the
format. The string generated by the conversion process is returned as the result
of this method.
If no format is specified the method defaults to text.
The specification of what a canonical serialization is can be found in the section
PEG serialization format.
The plugin has to conform to the interface documented in the Parser Tools Export
API specification.
objectName export object object ?format?
This method is a convenient wrapper around the export serial method described by
the previous item. It expects that object is an object command supporting a
serialize method returning the canonical serialization of a parsing expression
grammar. It invokes that method, feeds the result into export serial and returns
the resulting string as its own result.
objectName configuration names
This method returns a list containing the names of all configuration options
currently known to the object.
objectName configuration get
This method returns a dictionary containing the names and values of all
configuration options currently known to the object.
objectName configuration set name ?value?
This method sets the configuration option name to the specified value and returns
the new value of the option.
If no value is specified it simply returns the current value, without changing it.
Note that these configuration options and their values are simply passed to a
plugin when the actual export is performed. It is the plugin which checks the
validity, not the manager.
objectName configuration unset pattern...
This method unsets all configuration options matching the specified glob patterns.
If no pattern is specified it will unset all currently defined configuration
options.
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>