Ambient-Oriented Programming

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at:tutorial:appendix [2010/05/26 19:39] – *fixed tvcutsemat:tutorial:appendix [2024/10/03 22:19] (current) – fixing path to exceptions module elisag
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 ====== Appendix: Libraries ====== ====== Appendix: Libraries ======
  
-In the appendix, we explain useful libraries available to the AmbientTalk/2 programmer. These libraries provide abstractions ranging from traditional, established "collections" up to newly researched language constructs, such as "ambient references".+In the appendix, we explain useful libraries available to the AmbientTalk/2 programmer as part of the AmbientTalk standard library, also known as ''atlib''. These libraries provide abstractions ranging from traditional, established "collections" up to newly researched language constructs, such as "ambient references". 
 + 
 +The Ambientalk standard library (''atlib'') is part of the AmbientTalk/2 distribution. Note that the Intellij plugin already contains ''atlib''. If you would like to access the atlib source files, please visit the dedicated gitlab project [[ https://gitlab.soft.vub.ac.be/ambienttalk/atlib |here.]] 
  
 ===== Unit Testing Framework ===== ===== Unit Testing Framework =====
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 ===== Custom Exceptions ===== ===== Custom Exceptions =====
  
-The module ''/.at.exceptions'' defines a number of auxiliary methods which can be used to define one's own custom exceptions. Here is how to define a custom exception ''FooException''. First, define a new type tag with which clients of your code can catch the exception:+The module ''/.at.lang.exceptions'' defines a number of auxiliary methods which can be used to define one's own custom exceptions. Here is how to define a custom exception ''FooException''. First, define a new type tag with which clients of your code can catch the exception:
  
 <code> <code>
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 ===== Language Extensions ===== ===== Language Extensions =====
  
-The files in the ''at/lang'' directory define custom language features which mostly use AmbientTalk/2's reflective facilities to extend the language.+The files in the ''at/lang'' directory define custom language features which mostly use AmbientTalk/2's reflective facilities to extend the language. In what follows, we describe the most relevant ones. 
  
-==== Futures and Multifutures ==== 
  
-=== Futures ===+ 
 + 
 +=====Futures and Multifutures ===== 
 + 
 +==== Futures ====
  
 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 ''/.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.
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 </code> </code>
  
-Finally, the futures module also provides some auxiliary functions, of which ''group:'' is often a very useful one. The ''group:'' construct groups a table of futures into a single future which is resolved with a table of values or ruined with an exception:+The ''makeFuture'' function can also take a timeout. If a timeout is given it returns a returns a pair [lease, resolver]  where the lease timer gets immediately activated. If the future is not resolved within the given timeout, the lease expires and ruins the future with a ''TimeoutException''. Note that this means a lease will get parameter-passed rather than the future if given to other actors. 
 + 
 +=== Auxilary functions in the futures module ==== 
 + 
 +The futures module also provides some auxiliary functions, of which ''group:'' is often a very useful one. The ''group:'' construct groups a table of futures into a single future which is resolved with a table of values or ruined with an exception:
  
 <code> <code>
-when: (group: [ a<-m(), b<-n() ]) becomes: { |values|+when: (group: [ a<-m()@FutureMessage, b<-n()@FutureMessage ]) becomes: { |values|
   def [aResult, bResult] := values;   def [aResult, bResult] := values;
   ...   ...
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 </code> </code>
  
-=== Multifutures ===+Another useful auxilary function is ''future:'' construct which returns a future which is resolved with the value passed to the 'reply' closure: 
 + 
 +<code> 
 +future: { |return| 
 +  // some computation 
 +  return(val) 
 +} 
 +</code> 
 + 
 +This is actually equivalent to the slightly more verbose code: 
 + 
 +<code> 
 +def [fut,res] := makeFuture(); 
 +try: { // some computation 
 +  res.resolve(val); 
 +} catch: Exception using: { |e| res.ruin(e) } 
 +fut; 
 +</code> 
 + 
 +==== 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. 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.
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 When the message sent to a multireference is annotated with @Due(t), the timeout is applied to the implicit multifuture, causing whenAll observers to trigger automatically. Note that the implicit multifuture of a multireference is bounded, so whenAll observers trigger automatically when all replies have been received. When the message sent to a multireference is annotated with @Due(t), the timeout is applied to the implicit multifuture, causing whenAll observers to trigger automatically. Note that the implicit multifuture of a multireference is bounded, so whenAll observers trigger automatically when all replies have been received.
  
-==== Leased Object References ====+ 
 +===== Leased Object References =====
  
 The module ''/.at.lang.leasedrefs'' provides support for leased object references. Leased object references have already been described as part of the [[:at:tutorial:distribution#dealing_with_permanent_failures|distributed programing]] section in the tutorial. The module ''/.at.lang.leasedrefs'' provides support for leased object references. Leased object references have already been described as part of the [[:at:tutorial:distribution#dealing_with_permanent_failures|distributed programing]] section in the tutorial.
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 +===== TOTAM =====
  
-==== Dynamic Variables ====+The module ''/.at.lang.totam'' provides an implementation for TOTAM, a tuple space model geared towards mobile ad hoc networks which combines a replication-based tuple space model with a dynamic scoping mechanism that limits the transportation of tuples.  
 + 
 +Please have a look to [[:uf:totam]] for further details on the model and its API. 
 + 
 +===== 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. 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.
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 You can find more usage examples of dynamic variables in the unit test included in the file ''at/lang/dynvars.at''. 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 =====
  
 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: 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:
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 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. 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 ====+===== 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. 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.
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 More usage examples of structural types can be found in the unit test defined in the file ''at/lang/structuraltypes.at''. More usage examples of structural types can be found in the unit test defined in the file ''at/lang/structuraltypes.at''.
  
-==== Traits ====+===== Traits =====
  
 The module ''/.at.lang.traits'' exports a small library to use AmbientTalk's traits in a more structured manner. In the literature, traits are described as reusable components with two interfaces: an interface of methods that are //provided// by the trait //to// the composite and an interface of methods that are //required// by the trait //from// the composite. AmbientTalk's traits only make the provided interface explicit. The required interface remains implicit and unchecked at composition time. The module ''/.at.lang.traits'' exports a small library to use AmbientTalk's traits in a more structured manner. In the literature, traits are described as reusable components with two interfaces: an interface of methods that are //provided// by the trait //to// the composite and an interface of methods that are //required// by the trait //from// the composite. AmbientTalk's traits only make the provided interface explicit. The required interface remains implicit and unchecked at composition time.
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 The files in the ''at/support'' subdirectory of the standard library implement various utilities of use to the AmbientTalk programmer. We discuss the most useful modules below. The files in the ''at/support'' subdirectory of the standard library implement various utilities of use to the AmbientTalk programmer. We discuss the most useful modules below.
 +
  
 ==== Timing Utilities ==== ==== Timing Utilities ====
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 The timer module also defines a function ''whenever:elapsed:'' which repetitively invokes the given block closure every time the timeout period has elapsed. The returned subscription object can be used to eventually stop the repetitive invocation of the closure. The timer module also defines a function ''whenever:elapsed:'' which repetitively invokes the given block closure every time the timeout period has elapsed. The returned subscription object can be used to eventually stop the repetitive invocation of the closure.
  
-The timer module defines a small number of additional utility functions which can be found in the file ''at/support/timer.at''.+Finally, there is a variant of ''when:elapsed:'' called ''when:elapsedWithFuture:'' which returns a future that will be resolved or ruined by executing the given closure after the given timeout. This variant is very useful in unit tests, e.g: 
 + 
 +<code> 
 +def testAsyncNearbyPlayerReply(){ 
 +  def nearbyPlayers := // search 2 nearby player orjbects; 
 +  // wait a bit so that there are the 2 members. 
 +  when: 2.seconds elapsedWithFuture:{ 
 + self.assertEquals(2, nearbyPlayers.getReceivedAnswers); 
 +  } 
 +}; 
 +</code> 
  
 ==== Logging Framework ==== ==== Logging Framework ====
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