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--- at:tutorial:appendix [2008/07/10 16:02] – added tvcutsem
+++ at:tutorial:appendix [2008/07/10 16:23] – * tvcutsem
@@ Line 424: / Line 424: @@
 === Multifutures ===
-The module ''/.at.lang.multifutures'' provides support for multifutures. A multifuture is a future that can be resolved multiple times. We distinguish between 'bounded multifutures', which can be resolved up to a maximum number and 'unbounded multifutures' which have no upper bound. A multifuture accepts  the following listeners:
+The module ''/.at.lang.multifutures'' provides support for multifutures. A multifuture is a future that can be resolved multiple times. We distinguish between 'bounded multifutures', which can be resolved up to a maximum number and 'unbounded multifutures' which have no upper bound.
+A multifuture is constructed as follows:
+<code>
+def [mf, resolver] := makeMultiFuture(n, timeout);
+</code>
+The parameter ''n'' indicates the maximum number of values/exceptions with which the future can be resolved/ruined. If ''n'' is ''nil'', the multifuture is unbounded. The timeout parameter is optional. If not nil, it is a timeout period in milliseconds that causes the multifuture to //automatically// become fully resolved after the provided timeout. Once fully resolved, a multifuture will not accept any new values/exceptions, even if it has not reached its "upper bound" ''n'' yet.
+A multifuture accepts the following listeners:
 <code>
@@ Line 430: / Line 439: @@
 </code>
-This listener is invoked whenever the future is resolved with a new value. Its code can thus be executed multiple times.
+The above listener is invoked whenever the future is resolved with a new value. Its code can thus be executed multiple times.
 <code>
@@ Line 438: / Line 447: @@
 </code>
-This listener invoked if all results have been gathered (only possible if the maximum number of results is known). If there are no exceptions, only the first code block is triggered. If there are only exceptions, the first block is still invoked with an empty value table.
+The above listener is invoked if all results have been gathered (only possible if the maximum number of results is known) or when the ''timeout'' period associated with the future has elapsed. ''values'' refers to a table of all resolved values. If there are no exceptions, only the first code block is triggered. If there are only exceptions, the first block is still invoked with an empty table.
 Note the following properties of multifutures:
@@ Line 455: / 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 ====
 ==== Traits ====