pt_export_api(i) Parser Tools pt_export_api(i)______________________________________________________________________________NAME
pt_export_api - Parser Tools Export API
SYNOPSIS
package require Tcl 8.5
CONVERTER reset
CONVERTER configure
CONVERTER configure option
CONVERTER configure option value...
CONVERTER convert serial
::export serial configuration
_________________________________________________________________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 document describes two APIs. First the API shared by all packages
for the conversion of Parsing Expression Grammars into some other for‐
mat, and then the API shared by the packages which implement the export
plugins sitting on top of the conversion packages.
Its intended audience are people who wish to create their own converter
for some type of output, and/or an export plugin for their or some
other converter.
It resides in the Export section of the Core Layer of Parser Tools.
IMAGE: arch_core_export
CONVERTER API
Any (grammar) export converter has to follow the rules set out below:
[1] A converter is a package. Its name is arbitrary, however it is
recommended to put it under the ::pt::peg::to namespace.
[2] The package provides either a single Tcl command following the
API outlined below, or a class command whose instances follow
the same API. The commands which follow the API are called con‐
verter commands.
[3] A converter command has to provide the following three methods
with the given signatures and semantics. Converter commands are
allowed to provide more methods of their own, but not less, and
they may not provide different semantics for the standardized
methods.
CONVERTER reset
This method has to reset the configuration of the con‐
verter to its default settings. The result of the method
has to be the empty string.
CONVERTER configure
This method, in this form, has to return a dictionary
containing the current configuration of the converter.
CONVERTER configure option
This method, in this form, has to return the current
value of the specified configuration option of the con‐
verter.
Please read the section Options for the set of standard
options any converter has to accept. Any other options
accepted by a specific converter will be described in its
manpage.
CONVERTER configure option value...
This command, in this form, sets the specified options of
the converter to the given values.
Please read the section Options for the set of standard
options a converter has to accept. Any other options
accepted by a specific converter will be described in its
manpage.
CONVERTER convert serial
This method has to accept the canonical serialization of
a parsing expression grammar, as specified in section PEG
serialization format, and contained in serial. The
result of the method has to be the result of converting
the input grammar into whatever the converter is for, per
its configuration.
PLUGIN API
Any (grammar) export plugin has to follow the rules set out below:
[1] A plugin is a package.
[2] The name of a plugin package has the form pt::peg::export::FOO,
where FOO is the name of the format the plugin will generate
output for.
[3] The plugin can expect that the package pt::peg::export::plugin
is present, as indicator that it was invoked from a genuine
plugin manager.
It is recommended that a plugin does check for the presence of
this package.
[4] A plugin has to provide a single command, in the global names‐
pace, with the signature shown below. Plugins are allowed to
provide more command of their own, but not less, and they may
not provide different semantics for the standardized command.
::export serial configuration
This command has to accept the canonical serialization of
a parsing expression grammar and the configuration for
the converter invoked by the plugin. The result of the
command has to be the result of the converter invoked by
the plugin for th input grammar and configuration.
string serial
This argument will contain the canonical serial‐
ization of the parsing expression grammar for
which to generate the output. The specification
of what a canonical serialization is can be found
in the section PEG serialization format.
dictionary configuration
This argument will contain the configuration to
configure the converter with before invoking it,
as a dictionary mapping from options to values.
Please read the section Options for the set of
standard options any converter has to accept, and
thus any plugin as well. Any other options
accepted by a specific plugin will be described in
its manpage.
[5] A single usage cycle of a plugin consists of an invokation of
the command export. This call has to leave the plugin in a state
where another usage cycle can be run without problems.
OPTIONS
Each export converter and plugin for an export converter has to accept
the options below in their configure method. Converters are allowed to
ignore the contents of these options when performing a conversion, but
they must not reject them. Plugins are expected to pass the options
given to them to the converter they are invoking.
-file string
The value of this option is the name of the file or other entity
from which the grammar came, for which the command is run. The
default value is unknown.
-name string
The value of this option is the name of the grammar we are pro‐
cessing. The default value is a_pe_grammar.
-user string
The value of this option is the name of the user for which the
command is run. The default value is unknown.
USAGE
To use a converter do
# Get the converter (single command here, not class)
package require the-converter-package
# Provide a configuration
theconverter configure ...
# Perform the conversion
set result [theconverter convert $thegrammarserial]
... process the result ...
To use a plugin FOO do
# Get an export plugin manager
package require pt::peg::export
pt::peg::export E
# Provide a configuration
E configuration set ...
# Run the plugin, and the converter inside.
set result [E export serial $grammarserial FOO]
... process the result ...
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_export_api(i)
