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--- at:tutorial:appendix [2008/07/10 16:12] – * tvcutsem
+++ at:tutorial:appendix [2008/07/10 16:32] – * tvcutsem
@@ Line 392: / Line 392: @@
 === Futures ===
-The module ''/.at.lang.futures'' provides support for futures. Futures have already been described as part of the [[concurreny|concurrency]] section in the tutorial.
+The module ''/.at.lang.futures'' provides support for futures. Futures have already been described as part of the [[:at:tutorial:actors#futures|concurrency]] section in the tutorial.
 The module exports the type tags ''OnewayMessage'', ''FutureMessage'' and ''Due'':
@@ Line 464: / Line 464: @@
 ==== Dynamic Variables ====
+The module ''/.at.lang.dynvars'' provides support for defining and using 'Dynamic Variables'. Dynamic variables 'simulate' dynamically scoped variables and are often used to parameterize large parts of code. For example, the 'current output stream'. A dynamic variable has the advantage over a simple global variable that it can only be assigned a value for the extent of a block of code.
+A dynamic variable can be defined as follows:
+<code>
+def name := dynamicVariable: initialValue;
+</code>
+It can be read as follows:
+<code>
+?name or name.value
+</code>
+It can be assigned only within a limited dynamic scope, as follows:
+<code>
+with: name is: newval do: { code }
+// or
+name.is: newval in: { code }
+</code>
+When ''code'' terminates (either normally or via an exception), the dynamic variable is automatically reset to its previous value.
+By convention, we prefix the names of dynamic variables with a ''d'', e.g. ''dTimeoutPeriod''. This makes it easier to remember to access these variables by means of ''?'' or ''.value''.
+You can find more usage examples of dynamic variables in the unit test included in the file ''at/lang/dynvars.at''.
 ==== Ambient References ====
+Ambient references are defined in the module ''/.at.lang.ambientrefs'' . An ambient reference is a special kind of far reference which refers to an ever-changing collection of objects of a certain type. For example:
+<code>
+import /.at.lang.ambientrefs;
+deftype Printer;
+def printers := ambient: Printer;
+</code>
+In the above code, ''printers'' refers to all nearby objects exported by means of  the ''Printer'' type tag. An more in-depth explanation of ambient references can be found on the [[:research:ambientrefs|research page of ambient references]].
+Ambient references ship with two so-called "implementation modules": the module ''/.at.ambient.ar_extensional_impl'' and the module ''/.at.m2mi.ar_intensional_impl''. By default, the extensional implementation is used, but this can be changed by passing the desired implementation module as a parameter to the ''/.at.lang.ambientrefs'' module.
 ==== Structural Types ====
+The module ''/.at.lang.structuraltypes'' implements a small library to use structural typing. The library allows for the creation of 'protocols', which are first-class structural types. A structural type is simply a set of selectors. An object o conforms to a protocol P <=> for all selectors s of P, o respondsTo s where respondsTo is determined by o's mirror.
+A structural type can be branded with type tags. In this case, objects only conform to the type if they are structurally conformant **and** if they are tagged with the structural type's brands.
+Use the ''protocol:'' function to create a new protocol:
+<code>
+def PersonProtocol := protocol: {
+  def name;
+  def age;
+} named: `Person;
+</code>
+The ''`Person'' argument is used to give the protocol a name simply for display purposes. The ''object:implements:'' function automatically checks whether an object conforms to any declared types:
+<code>
+def tom := object: {
+  def name := "Tom";
+  def age() { 24 };
+} implements: PersonProtocol;
+</code>
+You can also create a protocol from an object:
+<code>def tomsProtocol := protocolOf: tom;</code>
+You can test protocol conformance in either of two styles:
+  * ''does: tom implement: PersonProtocol'' => true or false
+  * ''PersonProtocol <? tom'' => true or false
+You can also force a ''StructuralTypeMismatch'' exception to be raised if the object does not conform to the type:
+  *  ''ensure: tom implements: PersonProtocol'' => true or exception
+  *  ''PersonProtocol.checkConformance(tom)'' => true or exception
+More usage examples of structural types can be found in the unit test defined in the file ''at/lang/structuraltypes.at''.
 ==== Traits ====