pt::peg::export(n) Parser Tools pt::peg::export(n)______________________________________________________________________________NAME
pt::peg::export - PEG Export
SYNOPSIS
package require Tcl 8.5
package require snit
package require configuration
package require pt::peg
package require pluginmgr
package require pt::peg::export ?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 gram‐
mars 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 seri‐
alization 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\GRAM‐
MAR\PEG\EXPORT\PLUGINS"
[11] the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUG‐
INS"
[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 inter‐
action 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 associ‐
ated 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 behav‐
ior 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 spec‐
ified 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 configu‐
ration 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 sim‐
ply 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 speci‐
fied 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 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::export(n)
