File: bagel.html

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<title>Listing of doc/example-scripts/bagel.tcl</title>
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<body class="article">
<div id="header">
<h1>Listing of doc/example-scripts/bagel.tcl</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>This example is a straight translation of the OTcl Tutorial
<a href="http://www.isi.edu/nsnam/otcl/doc/tutorial.html">http://www.isi.edu/nsnam/otcl/doc/tutorial.html</a> to NX. It serves as
a very short intro to the basic elements of scripting with NX and
provides a comparison study to OTcl.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'><span class='nx-keyword'>package</span> req nx
nx::test <span class='nx-keyword'>configure</span> -count 1</pre></div></div>
<div class="paragraph"><p>Suppose we need to work with many bagels in our application. We
might start by creating a Bagel class.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Bagel
::Bagel</pre></div></div>
<div class="paragraph"><p>We can now create bagels and keep track of them using the info
method.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
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.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% Bagel <span class='nx-keyword'>create</span> abagel
::abagel

% abagel <span class='nx-keyword'>info</span> <span class='nx-keyword'>class</span>
::Bagel

% Bagel <span class='nx-keyword'>info</span> instances
::abagel</pre></div></div>
<div class="paragraph"><p>Of course, bagels don&#8217;t do much yet. They should remember whether
they&#8217;ve been toasted. We can create and access an instance variable
by defining a property for the class. All instance variables are
per default public in the sense of C++.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% Bagel <span class='nx-keyword'>property</span> {toasted 0}</pre></div></div>
<div class="paragraph"><p>Since abagel was created before the definition of the property we
have to set the default value for it using the setter method. Again,
the info method helps us keep track of things.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% abagel <span class='nx-keyword'>info</span> vars

% abagel <span class='nx-keyword'>configure</span> -toasted 0

% abagel <span class='nx-keyword'>info</span> vars
toasted

% abagel <span class='nx-keyword'>cget</span> -toasted
0</pre></div></div>
<div class="paragraph"><p>But we really want them to begin in an untoasted state to start
with.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% Bagel <span class='nx-keyword'>create</span> bagel2
::bagel2

% bagel2 <span class='nx-keyword'>info</span> vars
toasted

% bagel2 <span class='nx-keyword'>cget</span> -toasted
0</pre></div></div>
<div class="paragraph"><p>Our bagels now remember whether they&#8217;ve been toasted. Let is
recreate the first one.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% <span class='nx-keyword'>lsort</span> [Bagel <span class='nx-keyword'>info</span> instances]
::abagel ::bagel2

% ::abagel <span class='nx-keyword'>destroy</span>

% Bagel <span class='nx-keyword'>info</span> instances
::bagel2

% Bagel <span class='nx-keyword'>create</span> abagel
::abagel</pre></div></div>
<div class="paragraph"><p>Now we&#8217;re ready to add a method to bagels so that we can toast
them. Methods have an argument list and body like regular
Tcl procs. Here&#8217;s the toast method.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% Bagel <span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> toast {} {
      <span class='nx-keyword'>if</span> {[<span class='nx-keyword'>incr</span> :toasted] &gt; 1} then {
        <span class='nx-keyword'>error</span> <span class='nx-string'>"something's burning!"</span>
      }
}
::nsf::classes::Bagel::toast</pre></div></div>
<div class="paragraph"><p>The defined methods can be queried with info. We see as well the
setter method for the variable toasted.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% Bagel <span class='nx-keyword'>info</span> <span class='nx-keyword'>methods</span>
toast</pre></div></div>
<div class="paragraph"><p>Aside from setting the toasted variable, the body of the toast
method demonstrates how to access instance variables by using a
leading colon in the name.</p></div>
<div class="paragraph"><p>We invoke the toast method on bagels in the same way we use the
info and destroy methods that were provided by the system. That
is, there is no distinction between user and system methods.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% abagel toast
% abagel toast
something's burning!</pre></div></div>
<div class="paragraph"><p>Now we can add spreads to the bagels and start tasting them. If we
have bagels that aren&#8217;t topped, as well as bagels that are, we may
want to make toppable bagels a separate class. Let explore
inheritance with these two classes, starting by making a new class
SpreadableBagel that inherits from Bagel. A SpreadableBagel has a property toppings which might have multiple values. Initially,
toppings are empty.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> SpreadableBagel -superclass Bagel {
    <span class='nx-keyword'>:property</span> -incremental {toppings:0..n <span class='nx-string'>""</span>}
}
::SpreadableBagel

% SpreadableBagel <span class='nx-keyword'>cget</span> -superclass
::Bagel
% SpreadableBagel <span class='nx-keyword'>info</span> superclasses
::Bagel

% SpreadableBagel <span class='nx-keyword'>info</span> heritage
::Bagel ::nx::Object</pre></div></div>
<div class="paragraph"><p>Let&#8217;s add a taste method to bagels, splitting its functionality
between the two classes and combining it with next.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% Bagel <span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> taste {} {
    <span class='nx-keyword'>if</span> {<span class='nx-variable'>${</span><span class='nx-variable'>:toasted}</span> == 0} then {
    <span class='nx-keyword'>return</span> raw!
  } elseif {<span class='nx-variable'>${</span><span class='nx-variable'>:toasted}</span> == 1} then {
    <span class='nx-keyword'>return</span> toasty
  } <span class='nx-keyword'>else</span> {
    <span class='nx-keyword'>return</span> burnt!
  }
}
::nsf::classes::Bagel::taste

% SpreadableBagel <span class='nx-keyword'>public</span> <span class='nx-keyword'>method</span> taste {} {
    <span class='nx-keyword'>set</span> t [<span class='nx-keyword'>next</span>]
    <span class='nx-keyword'>foreach</span> i <span class='nx-variable'>${</span><span class='nx-variable'>:toppings}</span> {
       <span class='nx-keyword'>lappend</span> t <span class='nx-variable'>$i</span>
    }
    <span class='nx-keyword'>return</span> <span class='nx-variable'>$t</span>
}
::nsf::classes::SpreadableBagel::taste

% SpreadableBagel <span class='nx-keyword'>create</span> abagel
::abagel

% abagel toast
% abagel toppings add jam
jam
% abagel toppings add m&amp;m
m&amp;m jam

% abagel taste
toasty m&amp;m jam</pre></div></div>
<div class="paragraph"><p>Of course, along come sesame, onion, poppy, and a host of other
bagels, requiring us to expand our scheme. We could keep track of
flavor with an instance variable, but this may not be
appropriate. Flavor is an innate property of the bagels, and one
that can affect other behavior - you wouldn&#8217;t put jam on an onion
bagel, would you? Instead of making a class hierarchy, let&#8217;s use
multiple inheritance to make the flavor classes mixins that add a
their taste independent trait to bagels or whatever other food they
are mixed with.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Sesame {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> taste {} {<span class='nx-keyword'>concat</span> [<span class='nx-keyword'>next</span>] <span class='nx-string'>"sesame"</span>}
}
::Sesame

% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Onion {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> taste {} {<span class='nx-keyword'>concat</span> [<span class='nx-keyword'>next</span>] <span class='nx-string'>"onion"</span>}
}
::Onion

% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Poppy {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> taste {} {<span class='nx-keyword'>concat</span> [<span class='nx-keyword'>next</span>] <span class='nx-string'>"poppy"</span>}
}
::Poppy</pre></div></div>
<div class="paragraph"><p>Well, they don&#8217;t appear to do much, but the use of next allows them
to be freely mixed.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> SesameOnionBagel -superclass SpreadableBagel -mixin {Sesame Onion}
::SesameOnionBagel

% SesameOnionBagel <span class='nx-keyword'>create</span> abagel -toppings butter
::abagel

% abagel taste
raw! butter onion sesame</pre></div></div>
<div class="paragraph"><p>For multiple inheritance, the system determines a linear inheritance
ordering that respects all of the local superclass orderings. You
can examine this ordering with an info option. next follows this
ordering when it combines behavior.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% SesameOnionBagel <span class='nx-keyword'>info</span> heritage
::Sesame ::Onion ::SpreadableBagel ::Bagel ::nx::Object

% abagel <span class='nx-keyword'>info</span> precedence
::Sesame ::Onion ::SesameOnionBagel ::SpreadableBagel ::Bagel ::nx::Object</pre></div></div>
<div class="paragraph"><p>We can also combine our mixins with other classes, classes that need
have nothing to do with bagels, leading to a family of chips.</p></div>
<div class="listingblock">
<div class="content"><style type='text/css'>
.nx             {color: #000000; font-weight: normal; font-style: normal; padding-left: 10px}
table.nx        {border-collapse: collapse; border-spacing: 3px;}
.nx-linenr      {border-right: 1px solid #DDDDDD;padding-right: 5px; color: #2B547D;font-style: italic;}
.nx-string      {color: #779977; font-weight: normal; font-style: italic;}
.nx-comment     {color: #717ab3; font-weight: normal; font-style: italic;}
.nx-keyword     {color: #7f0055; font-weight: normal; font-style: normal;}
.nx-placeholder {color: #AF663F; font-weight: normal; font-style: italic;}
.nx-variable    {color: #AF663F; font-weight: normal; font-style: normal;}
</style>
<pre class='nx'>% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> Chips {
    <span class='nx-keyword'>:public</span> <span class='nx-keyword'>method</span> taste {} {<span class='nx-keyword'>return</span> <span class='nx-string'>"crunchy"</span>}
}
::Chips

% <span class='nx-keyword'>nx::Class</span> <span class='nx-keyword'>create</span> OnionChips -superclass Chips -mixin Onion
::OnionChips

% OnionChips <span class='nx-keyword'>create</span> abag
::abag

% abag taste
crunchy onion</pre></div></div>
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Last updated 2014-12-13 12:06:03 CET
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