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--- at:tutorial:appendix [2008/07/10 15:05] – * tvcutsem
+++ at:tutorial:appendix [2008/07/10 15:19] – added tvcutsem
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 The file ''at/collections/list.at'' contains a unit test that further illustrates the usage of the list datastructure.
+===== Top-level functions =====
+The file ''at/init/init.at'' shipped with the AmbientTalk/2 system library contains the code that is evaluated on startup within //every// actor created in the system. Because the definitions are evaluated in every actor's top-level scope, these  definitions will be globally visible in every file. Below, we describe the standard functionality provided by AmbientTalk/2's default ''init'' file.
+==== Asynchronous control structures ====
+The ''init'' file defines a number of useful control structures that operate asynchronously.
+''loop:'' defines an infinite asynchronous loop. That is, the block closure is executed, then asynchronously applied again:
+<code>
+loop: {
+  ...
+}
+</code>
+An ''if''-test on a future for a boolean:
+<code>
+whenTrue: booleanFuture then: { ... } else: { ... }
+</code>
+Asynchronous while loop over future-type conditional:
+<code>
+asLongAs: { /* asynchronous computation returning a future */ } do: { ... }
+</code>
+==== Mobile code ====
+The function ''script:carrying:'' can be used to define a "pass-by-copy" closure, as follows:
+<code>
+def mobileAdder(x) {
+  script: { |n| x + n } carrying: [`x]
+}
+</code>
+A call to ''mobileAdder(5)'' returns a closure which, when applied to a number, returns that number incremented with 5. Unlike regular closures, which are pass-by-far-reference when passing them to another actor, the above closure is pass-by-copy. The result is that a remote actor can apply the closure synchronously. The catch is that for this to work, the closure must specifically list all of its lexically free variables in the ''carrying:'' parameter. These variables will be copied along with the closure when it is parameter-passed.
+The constructor function ''isolate:passAs:'' allows you to define an isolate object with a custom serialization strategy. For example,
+<code>
+def foo := 42;
+def i := isolate: {
+  ...
+} passAs: { |foo|
+  /.some.Object.new(foo);
+}
+</code>
+The above code defines an isolate object ''i'' which, when passed between actors, becomes a ''some.Object'' on the other side. Note that state (''foo'' in the example) can be transferred as usual via the parameter list of the closure.