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<!DOCTYPE html><html><head>
<title>pt_export_api - Parser Tools</title>
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<div class="doctools">
<h1 class="doctools_title">pt_export_api(i) 1 tcllib &quot;Parser Tools&quot;</h1>
<div id="name" class="doctools_section"><h2><a name="name">Name</a></h2>
<p>pt_export_api - Parser Tools Export API</p>
</div>
<div id="toc" class="doctools_section"><h2><a name="toc">Table Of Contents</a></h2>
<ul class="doctools_toc">
<li class="doctools_section"><a href="#toc">Table Of Contents</a></li>
<li class="doctools_section"><a href="#synopsis">Synopsis</a></li>
<li class="doctools_section"><a href="#section1">Description</a></li>
<li class="doctools_section"><a href="#section2">Converter API</a></li>
<li class="doctools_section"><a href="#section3">Plugin API</a></li>
<li class="doctools_section"><a href="#section4">Options</a></li>
<li class="doctools_section"><a href="#section5">Usage</a></li>
<li class="doctools_section"><a href="#section6">PEG serialization format</a>
<ul>
<li class="doctools_subsection"><a href="#subsection1">Example</a></li>
</ul>
</li>
<li class="doctools_section"><a href="#section7">PE serialization format</a>
<ul>
<li class="doctools_subsection"><a href="#subsection2">Example</a></li>
</ul>
</li>
<li class="doctools_section"><a href="#section8">Bugs, Ideas, Feedback</a></li>
<li class="doctools_section"><a href="#keywords">Keywords</a></li>
<li class="doctools_section"><a href="#category">Category</a></li>
<li class="doctools_section"><a href="#copyright">Copyright</a></li>
</ul>
</div>
<div id="synopsis" class="doctools_section"><h2><a name="synopsis">Synopsis</a></h2>
<div class="doctools_synopsis">
<ul class="doctools_requirements">
<li>package require <b class="pkgname">Tcl 8.5</b></li>
</ul>
<ul class="doctools_syntax">
<li><a href="#1"><b class="cmd">CONVERTER</b> <b class="method">reset</b></a></li>
<li><a href="#2"><b class="cmd">CONVERTER</b> <b class="method">configure</b></a></li>
<li><a href="#3"><b class="cmd">CONVERTER</b> <b class="method">configure</b> <i class="arg">option</i></a></li>
<li><a href="#4"><b class="cmd">CONVERTER</b> <b class="method">configure</b> <i class="arg">option</i> <i class="arg">value</i>...</a></li>
<li><a href="#5"><b class="cmd">CONVERTER</b> <b class="method">convert</b> <i class="arg">serial</i></a></li>
<li><a href="#6"><b class="cmd">::export</b> <i class="arg">serial</i> <i class="arg">configuration</i></a></li>
</ul>
</div>
</div>
<div id="section1" class="doctools_section"><h2><a name="section1">Description</a></h2>
<p>Are you lost ?
Do you have trouble understanding this document ?
In that case please read the overview provided by the
<i class="term"><a href="pt_introduction.html">Introduction to Parser Tools</a></i>. This document is the
entrypoint to the whole system the current package is a part of.</p>
<p>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.</p>
<p>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.</p>
<p>It resides in the Export section of the Core Layer of Parser Tools.</p>
<p><img alt="arch_core_export" src="../../../../image/arch_core_export.png"></p>
</div>
<div id="section2" class="doctools_section"><h2><a name="section2">Converter API</a></h2>
<p>Any (grammar) export converter has to follow the rules set out below:</p>
<ol class="doctools_enumerated">
<li><p>A converter is a package. Its name is arbitrary, however it is
	recommended to put it under the <b class="namespace">::pt::peg::to</b>
	namespace.</p></li>
<li><p>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
	<i class="term">converter commands</i>.</p></li>
<li><p>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.</p>
<dl class="doctools_definitions">
<dt><a name="1"><b class="cmd">CONVERTER</b> <b class="method">reset</b></a></dt>
<dd><p>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.</p></dd>
<dt><a name="2"><b class="cmd">CONVERTER</b> <b class="method">configure</b></a></dt>
<dd><p>This method, in this form, has to return a dictionary containing the
current configuration of the converter.</p></dd>
<dt><a name="3"><b class="cmd">CONVERTER</b> <b class="method">configure</b> <i class="arg">option</i></a></dt>
<dd><p>This method, in this form, has to return the current value of the
specified configuration <i class="arg">option</i> of the converter.</p>
<p>Please read the section <span class="sectref"><a href="#section4">Options</a></span> 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.</p></dd>
<dt><a name="4"><b class="cmd">CONVERTER</b> <b class="method">configure</b> <i class="arg">option</i> <i class="arg">value</i>...</a></dt>
<dd><p>This command, in this form, sets the specified <i class="arg">option</i>s of the
converter to the given <i class="arg">value</i>s.</p>
<p>Please read the section <span class="sectref"><a href="#section4">Options</a></span> 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.</p></dd>
<dt><a name="5"><b class="cmd">CONVERTER</b> <b class="method">convert</b> <i class="arg">serial</i></a></dt>
<dd><p>This method has to accept the canonical serialization of a parsing
expression grammar, as specified in section
<span class="sectref"><a href="#section6">PEG serialization format</a></span>, and contained in <i class="arg">serial</i>.
The result of the method has to be the result of converting the input
grammar into whatever the converter is for, per its configuration.</p></dd>
</dl>
</li>
</ol>
</div>
<div id="section3" class="doctools_section"><h2><a name="section3">Plugin API</a></h2>
<p>Any (grammar) export plugin has to follow the rules set out below:</p>
<ol class="doctools_enumerated">
<li><p>A plugin is a package.</p></li>
<li><p>The name of a plugin package has the form
		pt::peg::export::<b class="variable">FOO</b>,
	where <b class="variable">FOO</b> is the name of the format the plugin will
	generate output for.</p></li>
<li><p>The plugin can expect that the package
	<b class="package">pt::peg::export::plugin</b> is present, as
	indicator that it was invoked from a genuine plugin manager.</p>
<p>It is recommended that a plugin does check for the presence of
	this package.</p></li>
<li><p>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.</p>
<dl class="doctools_definitions">
<dt><a name="6"><b class="cmd">::export</b> <i class="arg">serial</i> <i class="arg">configuration</i></a></dt>
<dd><p>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.</p>
<dl class="doctools_arguments">
<dt>string <i class="arg">serial</i></dt>
<dd><p>This argument will contain the <i class="term">canonical</i> serialization of the
parsing expression grammar for which to generate the output.
The specification of what a <i class="term">canonical</i> serialization is can be
found in the section <span class="sectref"><a href="#section6">PEG serialization format</a></span>.</p></dd>
<dt>dictionary <i class="arg">configuration</i></dt>
<dd><p>This argument will contain the configuration to configure the
converter with before invoking it, as a dictionary mapping from
options to values.</p>
<p>Please read the section <span class="sectref"><a href="#section4">Options</a></span> 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.</p></dd>
</dl></dd>
</dl>
</li>
<li><p>A single usage cycle of a plugin consists of an invokation of
	the command <b class="cmd"><a href="../../../../index.html#export">export</a></b>. This call has to leave the plugin in
	a state where another usage cycle can be run without problems.</p></li>
</ol>
</div>
<div id="section4" class="doctools_section"><h2><a name="section4">Options</a></h2>
<p>Each export converter and plugin for an export converter has to accept
the options below in their <b class="method">configure</b> 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.</p>
<dl class="doctools_options">
<dt><b class="option">-file</b> string</dt>
<dd><p>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 <b class="const">unknown</b>.</p></dd>
<dt><b class="option">-name</b> string</dt>
<dd><p>The value of this option is the name of the grammar we are processing.
The default value is <b class="const">a_pe_grammar</b>.</p></dd>
<dt><b class="option">-user</b> string</dt>
<dd><p>The value of this option is the name of the user for which the command
is run. The default value is <b class="const">unknown</b>.</p></dd>
</dl>
</div>
<div id="section5" class="doctools_section"><h2><a name="section5">Usage</a></h2>
<p>To use a converter do</p>
<pre class="doctools_example">
    # 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 ...
</pre>
<p>To use a plugin <b class="variable">FOO</b> do</p>
<pre class="doctools_example">
    # 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 ...
</pre>
</div>
<div id="section6" class="doctools_section"><h2><a name="section6">PEG serialization format</a></h2>
<p>Here we specify the format used by the Parser Tools to serialize
Parsing Expression Grammars as immutable values for transport,
comparison, etc.</p>
<p>We distinguish between <i class="term">regular</i> and <i class="term">canonical</i>
serializations.
While a PEG may have more than one regular serialization only exactly
one of them will be <i class="term">canonical</i>.</p>
<dl class="doctools_definitions">
<dt>regular serialization</dt>
<dd><ol class="doctools_enumerated">
<li><p>The serialization of any PEG is a nested Tcl dictionary.</p></li>
<li><p>This dictionary holds a single key, <b class="const">pt::grammar::peg</b>, and its
value. This value holds the contents of the grammar.</p></li>
<li><p>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</p>
<dl class="doctools_definitions">
<dt><b class="const">rules</b></dt>
<dd><p>The value is a Tcl dictionary whose keys are the names of the
nonterminal symbols known to the grammar.</p>
<ol class="doctools_enumerated">
<li><p>Each nonterminal symbol may occur only once.</p></li>
<li><p>The empty string is not a legal nonterminal symbol.</p></li>
<li><p>The value for each symbol is a Tcl dictionary itself. The relevant
keys and their values in this dictionary are</p>
<dl class="doctools_definitions">
<dt><b class="const">is</b></dt>
<dd><p>The value is the serialization of the parsing expression describing
the symbols sentennial structure, as specified in the section
<span class="sectref"><a href="#section7">PE serialization format</a></span>.</p></dd>
<dt><b class="const">mode</b></dt>
<dd><p>The value can be one of three values specifying how a parser should
handle the semantic value produced by the symbol.</p>
<dl class="doctools_definitions">
<dt><b class="const">value</b></dt>
<dd><p>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.</p></dd>
<dt><b class="const">leaf</b></dt>
<dd><p>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.</p></dd>
<dt><b class="const">void</b></dt>
<dd><p>The nonterminal has no semantic value. Any ASTs generated by the
symbol's right hand side are discarded (as well).</p></dd>
</dl></dd>
</dl>
</li>
</ol></dd>
<dt><b class="const">start</b></dt>
<dd><p>The value is the serialization of the start parsing expression of the
grammar, as specified in the section <span class="sectref"><a href="#section7">PE serialization format</a></span>.</p></dd>
</dl>
</li>
<li><p>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.</p></li>
</ol></dd>
<dt>canonical serialization</dt>
<dd><p>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.</p>
<ol class="doctools_enumerated">
<li><p>The keys found in all the nested Tcl dictionaries are sorted in
ascending dictionary order, as generated by Tcl's builtin command
<b class="cmd">lsort -increasing -dict</b>.</p></li>
<li><p>The string representation of the value is the canonical representation
of a Tcl dictionary. I.e. it does not contain superfluous whitespace.</p></li>
</ol></dd>
</dl>
<div id="subsection1" class="doctools_subsection"><h3><a name="subsection1">Example</a></h3>
<p>Assuming the following PEG for simple mathematical expressions</p>
<pre class="doctools_example">
PEG calculator (Expression)
    Digit      &lt;- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;
    Sign       &lt;- '-' / '+'                                     ;
    Number     &lt;- Sign? Digit+                                  ;
    Expression &lt;- Term (AddOp Term)*                            ;
    MulOp      &lt;- '*' / '/'                                     ;
    Term       &lt;- Factor (MulOp Factor)*                        ;
    AddOp      &lt;- '+'/'-'                                       ;
    Factor     &lt;- '(' Expression ')' / Number                   ;
END;
</pre>
<p>then its canonical serialization (except for whitespace) is</p>
<pre class="doctools_example">
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}
}
</pre>
</div>
</div>
<div id="section7" class="doctools_section"><h2><a name="section7">PE serialization format</a></h2>
<p>Here we specify the format used by the Parser Tools to serialize
Parsing Expressions as immutable values for transport, comparison,
etc.</p>
<p>We distinguish between <i class="term">regular</i> and <i class="term">canonical</i>
serializations.
While a parsing expression may have more than one regular
serialization only exactly one of them will be <i class="term">canonical</i>.</p>
<dl class="doctools_definitions">
<dt>Regular serialization</dt>
<dd><dl class="doctools_definitions">
<dt><b class="const">Atomic Parsing Expressions</b></dt>
<dd><ol class="doctools_enumerated">
<li><p>The string <b class="const">epsilon</b> is an atomic parsing expression. It matches
the empty string.</p></li>
<li><p>The string <b class="const">dot</b> is an atomic parsing expression. It matches
any character.</p></li>
<li><p>The string <b class="const">alnum</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">alpha</b> is an atomic parsing expression. It matches
any Unicode alphabet character. This is a custom extension of PEs
based on Tcl's builtin command <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">ascii</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">control</b> is an atomic parsing expression. It matches
any Unicode control character. This is a custom extension of PEs based
on Tcl's builtin command <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">digit</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">graph</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">lower</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">print</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">punct</b> is an atomic parsing expression. It matches
any Unicode punctuation character. This is a custom extension of PEs
based on Tcl's builtin command <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">space</b> is an atomic parsing expression. It matches
any Unicode space character. This is a custom extension of PEs based
on Tcl's builtin command <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">upper</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">wordchar</b> 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 <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">xdigit</b> is an atomic parsing expression. It matches
any hexadecimal digit character. This is a custom extension of PEs
based on Tcl's builtin command <b class="cmd">string is</b>.</p></li>
<li><p>The string <b class="const">ddigit</b> is an atomic parsing expression. It matches
any decimal digit character. This is a custom extension of PEs based
on Tcl's builtin command <b class="cmd">regexp</b>.</p></li>
<li><p>The expression
    [list t <b class="variable">x</b>]
is an atomic parsing expression. It matches the terminal string <b class="variable">x</b>.</p></li>
<li><p>The expression
    [list n <b class="variable">A</b>]
is an atomic parsing expression. It matches the nonterminal <b class="variable">A</b>.</p></li>
</ol></dd>
<dt><b class="const">Combined Parsing Expressions</b></dt>
<dd><ol class="doctools_enumerated">
<li><p>For parsing expressions <b class="variable">e1</b>, <b class="variable">e2</b>, ... the result of
    [list / <b class="variable">e1</b> <b class="variable">e2</b> ... ]
is a parsing expression as well.
This is the <i class="term">ordered choice</i>, aka <i class="term">prioritized choice</i>.</p></li>
<li><p>For parsing expressions <b class="variable">e1</b>, <b class="variable">e2</b>, ... the result of
    [list x <b class="variable">e1</b> <b class="variable">e2</b> ... ]
is a parsing expression as well.
This is the <i class="term">sequence</i>.</p></li>
<li><p>For a parsing expression <b class="variable">e</b> the result of
    [list * <b class="variable">e</b>]
is a parsing expression as well.
This is the <i class="term">kleene closure</i>, describing zero or more
repetitions.</p></li>
<li><p>For a parsing expression <b class="variable">e</b> the result of
    [list + <b class="variable">e</b>]
is a parsing expression as well.
This is the <i class="term">positive kleene closure</i>, describing one or more
repetitions.</p></li>
<li><p>For a parsing expression <b class="variable">e</b> the result of
    [list &amp; <b class="variable">e</b>]
is a parsing expression as well.
This is the <i class="term">and lookahead predicate</i>.</p></li>
<li><p>For a parsing expression <b class="variable">e</b> the result of
    [list ! <b class="variable">e</b>]
is a parsing expression as well.
This is the <i class="term">not lookahead predicate</i>.</p></li>
<li><p>For a parsing expression <b class="variable">e</b> the result of
    [list ? <b class="variable">e</b>]
is a parsing expression as well.
This is the <i class="term">optional input</i>.</p></li>
</ol></dd>
</dl></dd>
<dt>Canonical serialization</dt>
<dd><p>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.</p>
<ol class="doctools_enumerated">
<li><p>The string representation of the value is the canonical representation
of a pure Tcl list. I.e. it does not contain superfluous whitespace.</p></li>
<li><p>Terminals are <em>not</em> encoded as ranges (where start and end of the
range are identical).</p></li>
</ol></dd>
</dl>
<div id="subsection2" class="doctools_subsection"><h3><a name="subsection2">Example</a></h3>
<p>Assuming the parsing expression shown on the right-hand side of the
rule</p>
<pre class="doctools_example">
    Expression &lt;- Term (AddOp Term)*
</pre>
<p>then its canonical serialization (except for whitespace) is</p>
<pre class="doctools_example">
    {x {n Term} {* {x {n AddOp} {n Term}}}}
</pre>
</div>
</div>
<div id="section8" class="doctools_section"><h2><a name="section8">Bugs, Ideas, Feedback</a></h2>
<p>This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category <em>pt</em> of the
<a href="http://core.tcl.tk/tcllib/reportlist">Tcllib Trackers</a>.
Please also report any ideas for enhancements you may have for either
package and/or documentation.</p>
<p>When proposing code changes, please provide <em>unified diffs</em>,
i.e the output of <b class="const">diff -u</b>.</p>
<p>Note further that <em>attachments</em> are strongly preferred over
inlined patches. Attachments can be made by going to the <b class="const">Edit</b>
form of the ticket immediately after its creation, and then using the
left-most button in the secondary navigation bar.</p>
</div>
<div id="keywords" class="doctools_section"><h2><a name="keywords">Keywords</a></h2>
<p><a href="../../../../index.html#ebnf">EBNF</a>, <a href="../../../../index.html#ll_k_">LL(k)</a>, <a href="../../../../index.html#peg">PEG</a>, <a href="../../../../index.html#tdpl">TDPL</a>, <a href="../../../../index.html#context_free_languages">context-free languages</a>, <a href="../../../../index.html#expression">expression</a>, <a href="../../../../index.html#grammar">grammar</a>, <a href="../../../../index.html#matching">matching</a>, <a href="../../../../index.html#parser">parser</a>, <a href="../../../../index.html#parsing_expression">parsing expression</a>, <a href="../../../../index.html#parsing_expression_grammar">parsing expression grammar</a>, <a href="../../../../index.html#push_down_automaton">push down automaton</a>, <a href="../../../../index.html#recursive_descent">recursive descent</a>, <a href="../../../../index.html#state">state</a>, <a href="../../../../index.html#top_down_parsing_languages">top-down parsing languages</a>, <a href="../../../../index.html#transducer">transducer</a></p>
</div>
<div id="category" class="doctools_section"><h2><a name="category">Category</a></h2>
<p>Parsing and Grammars</p>
</div>
<div id="copyright" class="doctools_section"><h2><a name="copyright">Copyright</a></h2>
<p>Copyright &copy; 2009 Andreas Kupries &lt;andreas_kupries@users.sourceforge.net&gt;</p>
</div>
</div></body></html>