Open Source Rule Engines in Java

Manageability - Open Source Rule Engines Written In Java

I don't recall if someone has put together a list of open source Rule Engines that are written in Java. Here's the list I've accumulated so far...
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Converting Array to List in Scala

Now, this has to have a built-in somewhere in Scala, because it just seems too common. So, how to convert an Array to a List in Scala?

Why do I need this? I needed to drop to Java for some functionality, which in this case returns an Array. I wanted to get that Array into a List to practice my functional programming skillz.

**Update**: I figured out how to convert Arrays to Lists the Scala way. Turns out it's a piece of cake.

val myList = List.fromArray(Array("one", "two", "three"))

or

val myList = Array("one","two","three").elements.toList

The call to elements returns an Iterator, and from there you can convert to a List via toList. Nice.

Because my first version wasn't actually tail recursive, what follows is a true tail recursive solution, if I were to implement this by hand. The above, built in mechanism is much better, though.


object ArrayUtil {
def toList[a](array: Array[a]): List[a] = {
def convert(ar…
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I ported a JavaScript app to Dart. Here's what I learned.

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In which I port a snazzy little JavaScript audio web app to Dart, discover a bug, and high-five type annotations. Here's what I learned.

[As it says in the header of this blog, I'm a seasoned Dart developer. However, I certainly don't write Dart every day (I wish!). Don't interpret this post as "Hi, I'm new to Dart". Instead, interpret this post as "I'm applying what I've been documenting."]

This post analyzes two versions of the same app, both the original (JavaScript) version and the Dart version. The original version is a proxy for any small JavaScript app, there's nothing particularly special about the original version, which is why it made for a good example.

This post discusses the differences between the two implementations: file organization, dependencies and modules, shims, classes, type annotations, event handling, calling multiple methods, asynchronous programming, animation, and interop with JavaScript libraries. Finally, I …
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Null-aware operators in Dart

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Three new language features just landed in the latest dev channel build of the Dart! Collectively known as null-aware operators, these new features will help you reduce the code required to work with potentially null objects.

I'm excited for these new abilities, because typing less is always a good thing. Read on to learn more, and be sure to try these new features on Dart Pad.

?? Use ?? when you want to evaluate and return an expression IFF another expression resolves to null.

exp ?? otherExp
is similar to

((x) => x == null ? otherExp : x)(exp)
??= Use ??= when you want to assign a value to an object IFF that object is null. Otherwise, return the object.

obj ??= value
is similar to

((x) => x == null ? obj = value : x)(obj)
?. Use ?. when you want to call a method/getter on an object IFF that object is not null (otherwise, return null).

obj?.method()
is similar to

((x) => x == null ? null : x.method())(obj)
You can chain ?. calls, for example:

…
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