Inspiration

From the syntactical point of view, urbiscript belongs to the C-family of programming languages.

Its prototype-based object-oriented design was influenced by the Self and the Io programming languages.^[2]

It is designed to program, but also interact with robots;^[2] as such, it is influenced by Unix shells and other languages that provide a read-eval-print loop 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:

 1 + 1; sleep(1s); 1 + 2 * 3;

[00005420] 2

[00006420] 7

Sequential statements and control flow

urbiscript statements include (among others):^[4]

• The if statement, which conditionally executes a block of code, along with else.
• The traditional for statement, as in C which iterates over an iterable object, capturing each element to a local variable for use by the attached block.
• Another for statement, which iterates over an iterable object, capturing each element to a local variable for use by the attached block.
• The while statement, which executes a block of code as long as its condition is true.
• The try statement, 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.
• The assert statement, 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.

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:

  var status = { if (closed) "closed" else "open" };
  var pass = { try { foo } catch { false } else { true } };

Concurrent statements and control flow

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 coroutines.^[5]

  {
    { sleep(2s); echo(2) },
    { sleep(1s); echo(1) }, 
  };
  echo(3);

  // This is actually "for;".
  for (var i : [0, 1, 2])
  {
    echo(i);
    echo(i ** 2);
  };

  for& (var i : [0, 1, 2])
  {
    echo(i);
    echo(i ** 2);
  };

Event-based programming

Aiming at the development of portable robotic applications,^[6] 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".

  var e = Event.new;

  at (e?)
    echo("received event e");

  e!;

  at (e?(1, var x) if x % 2 == 0)
    echo("received event e(1, %s)" % x);
  e!(1, 1);

  e!(1, 2);

  at (batteryLevel <= 0.2)
    robot.goToChargingDock;

  var x = 0;

  var y = 0;

  var z = 0;

  at (x + y == z)
    echo("%s + %s == %s" % [x, y, z]);

  x = 1;

  z = 1;