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Scala Actors -- A Short Tutorial

draganigajic — 2011-07-13T18:13:52+02:00

With the advent of multi-core processors concurrent programming is becoming indispensable. Scala's primary concurrency construct is actors. Actors are basically concurrent processes that communicate by exchanging messages. Actors can also be seen as a form of active objects where invoking a method corresponds to sending a message. The Scala Actors library provides both asynchronous and synchronous message sends (the latter are implemented by exchanging several asynchronous messages). Moreover, actors may communicate using futures where requests are handled asynchronously, but return a representation (the future) that allows to await the reply. This tutorial is mainly designed as a walk-through of several complete example programs Our first example consists of two actors that exchange a bunch of messages and then terminate. The first actor sends "ping" messages to the second actor, which in turn sends "pong" messages back (for each received "ping" message one "pong" message).

Defining Scala Design Idioms - Code Commit

draganigajic — 2011-07-13T18:13:52+02:00

All of these samples perform essentially the same task: traverse an array of strings and print each value to stdout. Of course, the C++ example is actually using a vector rather than an array due to the evil nature of C/C++ arrays, but it comes to the same thing. Passing over the differences in syntax between these four languages, what really stands out are the different ways in which the task is performed. C++ and Java are both using iterators, while Ruby and Scala are making use of higher order functions. Ruby and C++ both use lowercase variables separated by underscores, while Java and Scala share the camelCase convention. This is a bit of a trivial example, but it does open the door to a much more interesting discussion: what are these idioms in Scala’s case? Scala is a very new language which has yet to see truly wide-spread adoption. More than that, Scala is fundamentally different from what has come before.

Monads in Scala tutorial

draganigajic — 2011-07-13T18:13:52+02:00

emir burak In Informatics, there are two (related) meanings of the word "monad": * A triple (T,eta,mu) following some laws in category theory * A way of structuring functional programs The first meaning can probably not be described easily in natural language. Michael Arbib and Ernest Manes' "Arrows, Structure, Functors - The Categorical Imperative". describe them as (generalized monoids) in Section 10.2 and through adjointness to the forgetful functor from algebras to sets. That last connection basically makes everything that we can write down or model using abstract syntax / universal algebra a monad. The second view is described in Wadler's papers. I mention category theory because we can describe things that are not computations as monads. It also reminds us why a monad is a collection of things taken together. With the List example in mind, a potentially more revealing account on monads (aka triples) can be found in the free book Barr, Wells