urbiscript

<h2 id="syntax-and-semantics">Syntax and semantics</h2>
<h3>Inspiration</h3>
<p>From the syntactical point of view, urbiscript belongs to the <a href="/facts/C_(programming_language)/Ky2No763">C</a>-family of programming languages.
</p><p>Its prototype-based object-oriented design was influenced by the <a href="/facts/Self_(programming_language)/sBp39553">Self</a> and the <a href="/facts/Io_(programming_language)/06xtsq15">Io</a> programming languages.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>
</p><p>It is designed to program, but also interact with robots;<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> as such, it is influenced by <a href="/facts/Unix_shells/2G4T2Fb9">Unix shells</a> and other languages that provide a <a href="/facts/Read%25E2%2580%2593eval%25E2%2580%2593print_loop/lddjCYxt">read-eval-print loop</a> style interactive toplevel.  However, contrary to others, there is no prompt for user input but answers from the system are prefixed by a timestamp (in milliseconds) between square brackets:
</p>
 1 + 1; sleep(1s); 1 + 2 * 3;

<016>[00005420] 2
<016>[00006420] 7
<h3>Sequential statements and control flow</h3>
<p>urbiscript statements include (among others):<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<ul><li>The <a href="/facts/If-then-else/8gDQTqUD">if statement</a>, which conditionally executes a block of code, along with else.</li>
<li>The traditional <a href="/facts/For_loop/cwV2nRzp">for statement</a>, as in C which iterates over an iterable object, capturing each element to a local variable for use by the attached block.</li>
<li>Another <a href="/facts/Foreach_loop/wQzIwX3k">for statement</a>, which iterates over an iterable object, capturing each element to a local variable for use by the attached block.</li>
<li>The <a href="/facts/While_loop/hLrKdAFo">while statement</a>, which executes a block of code as long as its condition is true.</li>
<li>The <a href="/facts/Exception_handling/VrJxgb9r">try statement</a>, which allows exceptions thrown in its attached code block to be caught and handled by catch clauses.  An optional else clause is run if no exception was thrown.  Clean-up code can be guaranteed to be run in every case when given in a finally-clause.</li>
<li>The <a href="/facts/Assertion_(programming)/lxSfLdLY">assert statement</a>, used during debugging to check for conditions that ought to apply.  urbiscript also feature assert blocks, which can be used to factor several assert statements.</li></ul>
<p>Actually, contrary to most C-like languages and despite what the syntax suggests, statements "have a value", and therefore are expressions, provided they are embedded in braces:
</p>
  var status = { if (closed) "closed" else "open" };
  var pass = { try { foo } catch { false } else { true } };

<h3>Concurrent statements and control flow</h3>
<p>In urbiscript, some control-flow constructs come in several "flavors": two types of sequential composition, and two types of concurrent composition.  Under the hood, concurrency is implemented using <a href="/facts/Coroutine/hGCtXsAQ">coroutines</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>
<h4>Statement composition</h4>
<p>Like in C, the semicolon denotes sequential composition: a;b stands for "run statement a then run statement b.  Other tasks may be run between a and b.  Another statement separator, pipe, denotes "tight sequential composition": no other task can be run between a and b in a|b.
</p><p>Similarly urbiscript features two means to compose statements concurrently.  With a,b, first a is run, and at some point b will be --- possibly while a is still running.  This is very similar to the <a href="/facts/Job_control_(Unix)/NIzeWzjq">&</a> operator in Unix shells.  Alternatively, with a&b, both a and b are started together; in interactive sessions, this means that a won't be run until b is fully entered and properly followed by either a ; or a ,.
</p><p>Scopes are boundaries for backgrounded jobs, as demonstrated in the following example:<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p>
  {
    { sleep(2s); echo(2) },
    { sleep(1s); echo(1) }, 
  };
  echo(3);

<016>[00012451] *** 1
<016>[00013447] *** 2
<016>[00013447] *** 3
<h4>Concurrent flavors of sequential constructs</h4>
<p>Most looping constructs in urbiscript come in several "flavors", which are based on the four statement separators: ;, |, ,, and &.
</p><p>For instance
</p>
  // This is actually "for;".
  for (var i : [0, 1, 2])
  {
    echo(i);
    echo(i ** 2);
  };

<p>displays
</p>
<016>[00002919] *** 0
<016>[00002921] *** 0
<016>[00002921] *** 1
<016>[00002922] *** 1
<016>[00002922] *** 2
<016>[00002922] *** 4
<p>i.e., the loop bodies are not executed sequentially, while the for& keyword runs the loop bodies concurrently:
</p>
  for& (var i : [0, 1, 2])
  {
    echo(i);
    echo(i ** 2);
  };

<016>[00021680] *** 0
<016>[00021680] *** 1
<016>[00021680] *** 2
<016>[00021682] *** 0
<016>[00021682] *** 1
<016>[00021682] *** 4
<h3>Event-based programming</h3>
<p>Aiming at the development of portable robotic applications,<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> urbiscript relies on specific syntactic constructs to specify reactive behaviors such as "go to the charging dock when the battery is low", "play a friendly sound when a known face is recognized", or "stop when an obstacle is detected".
</p>
<h4>Explicit event handling</h4>
<p>Event handling goes into three steps.  First, define an event
</p>
  var e = Event.new;

<p>Second, specify event handlers
</p>
  at (e?)
    echo("received event e");

<p>Third, "emit" this event
</p>
  e!;

<016>[00014333] *** received event e
<p>Events can have payloads, and event handlers enjoy pattern matching on the payload:
</p>
  at (e?(1, var x) if x % 2 == 0)
    echo("received event e(1, %s)" % x);
  e!(1, 1);

<016>[00014336] *** received event e
  e!(1, 2);

<016>[00014336] *** received event e
<016>[00014336] *** received event e(1, 2)
<h4>Implicit events</h4>
<p>The urbiscript language also allows to monitor expressions:
</p>
  at (batteryLevel <= 0.2)
    robot.goToChargingDock;

<p>The following example demonstrates the feature:
</p>
  var x = 0;

<016>[00002165] 0
  var y = 0;

<016>[00002166] 0
  var z = 0;

<016>[00002167] 0
  at (x + y == z)
    echo("%s + %s == %s" % [x, y, z]);

<016>[00002168] *** 0 + 0 == 0
  x = 1;

<016>[00002169] 1
  z = 1;

<016>[00002170] 1
<016>[00002170] *** 1 + 0 == 1
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/URBI/TKK9EDsD">Urbi</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://github.com/urbiforge/urbi">urbi</a> on <a href="/facts/GitHub/n1hNCsc3">GitHub</a></li>
<li><a href="https://hub.docker.com/r/urbiforge/urbi/">Docker repository</a></li>
<li><a href="https://github.com/urbiforge/urbi/blob/master/doc/urbi-sdk.pdf">urbiscript Tutorial</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Baillie, Jean-Christophe (8 July 2008). "Urbi: a new parallel & event-driven script language for robotics, games and more". YouTube. Retrieved 6 Oct 2011. <a href="https://www.youtube.com/watch?v=FFLiIu2PtHQ" target="_blank">https://www.youtube.com/watch?v=FFLiIu2PtHQ</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Baillie, Jean-Christophe; Demaille, Akim; Nottale, Matthieu; Hocquet, Quentin; Tardieu, Samuel (2008). "The Urbi Universal Platform for Robotics" (PDF). Retrieved 6 October 2011. <a href="http://www.rfc1149.net/download/documents/scpr2008-08-Baillie.pdf" target="_blank">http://www.rfc1149.net/download/documents/scpr2008-08-Baillie.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Baillie, Jean-Christophe; Demaille, Akim; Nottale, Matthieu; Hocquet, Quentin; Tardieu, Samuel (2008). "The Urbi Universal Platform for Robotics" (PDF). Retrieved 6 October 2011. <a href="http://www.rfc1149.net/download/documents/scpr2008-08-Baillie.pdf" target="_blank">http://www.rfc1149.net/download/documents/scpr2008-08-Baillie.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"urbiscript Language Reference Manual". Retrieved 2011-09-20. <a href="http://gostai.com/downloads/urbi-sdk/2.8/doc/urbi-sdk.htmldir/urbiscript-language-reference-manual.html" target="_blank">http://gostai.com/downloads/urbi-sdk/2.8/doc/urbi-sdk.htmldir/urbiscript-language-reference-manual.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Baillie, Jean-Christophe; Demaille, Akim; Nottale, Matthieu; Hocquet, Quentin (2010). "Tag: Job Control in urbiscript" (PDF). Retrieved 6 October 2011. <a href="http://car.ensm-douai.fr/CAR2010/Papers/6-baillie-car2010.pdf" target="_blank">http://car.ensm-douai.fr/CAR2010/Papers/6-baillie-car2010.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Baillie, Jean-Christophe; Demaille, Akim; Nottale, Matthieu; Hocquet, Quentin (2010). "Tag: Job Control in urbiscript" (PDF). Retrieved 6 October 2011. <a href="http://car.ensm-douai.fr/CAR2010/Papers/6-baillie-car2010.pdf" target="_blank">http://car.ensm-douai.fr/CAR2010/Papers/6-baillie-car2010.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Baillie, Jean-Christophe; Demaille, Akim; Nottale, Matthieu; Hocquet, Quentin (2010). "Events! (Reactivity in urbiscript)". arXiv:1010.5694 [cs.PL]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
</ol>

urbiscript open-in-new

urbiscript