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 format, 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 converter
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 converter 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 converter.
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 namespace, 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 serialization 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 processing. 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 ...
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}
}
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.
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>