Functional programming a brief introduction to Scala

In this blogpost I’ll try to explain on a very basic level what functional programming (FP) is about. look at is as an introduction to the amazing world of FP. FP is already here for quite a few decades. It was mostly used in the academic world and specialized industries. Since the coming of Scala http://www.scala-lang.org, FP became more and more mainstream.

So what is functional programming?

(from Wikipedia http://en.wikipedia.org/wiki/Functional_programming) In computer sciencefunctional programming is a programming paradigm, a style of building the structure and elements of computer programs, that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It is a declarative programming paradigm, which means programming is done with expressions. In functional code, the output value of a function depends only on the arguments that are input to the function, so calling a function f twice with the same value for an argument x will produce the same resultf(x) each time. Eliminating side effects, i.e. changes in state that do not depend on the function inputs, can make it much easier to understand and predict the behavior of a program, which is one of the key motivations for the development of functional programming.

Installing Scala

I’m using the scala Read-Evaluate-Print-Loop (REPL) to show you the examples. It’s basically a Scala commandline interpreter. Just get the latest version of scala and install it. To get started with scala REPL, open a command prompt or terminal session; go to the directory where you installed scala and further to the bin directory. Enter the command scala or ./scala and you’re ready to go!

Read-Evaluate-Print-Loop

Scala Command line REPL

Scala

Scala is a programming language that mixes paradigms of both FP and OO. Scala uses its own compiler (scalac) to compile your code to byte code. Probably the biggest advantage of Scala is that it runs on your standard java infrastructure. It is even capable of calling your java code and visa versa although you need to take special care when integrating both languages. It’s functional As the name already states, functional programming allows the developer write your code on a functional level. In other words you don’t have to translate your functional solution to a lower, technical, level. If I want to know the outcome of: all even numbers between 1 and 10 and multiplied them by 2, you write in Scala

(1 to 10).toList.filter(_ % 2 == 0).map(_ * 2)

While in java it looks more like this

List input = {1,2,3,4,5,6,7,8,9,10}.toList();
List results = new ArrayList();
for(int val : input) {
  if(val % 2 == 0) {
    results.add(val * 2);
  }
}
return results;

Looking at the Scala code you will notice a few things.

  • The code is expressive and readable. No clutter, no unnecessary boiler plate code.
  • There is no assignment of variables (stateless)
  • Functions (_ % 2) and (_ * 2) is added as argument to a method
    • The underscore (_) represents a wildcard. In this case, each element of the list

Expressive

Scala, as all functional languages, is an expressive language. But what does it mean? First of all, it makes your code much more readable. You almost program what you say. A friend of mine, who’s working in the travel business, understood a Scala code snippet, while the java counterpart was Chinese for her. Is this important? Yes, if you know that code is read 10 times more than written.
Secondly expressions return values. Which can lead to less code.

Boilerplate code be gone!

The guys from Scala did their best to make the code as clean as possible. Every character unnecessary to run your code can be made obsolete. This includes ( ) for zero argument method calls, semi colons ‘;’, points ‘.’ etc… The scala compiler is quite intelligent and will do all the hard work for you to convert the dense code into the full-blown byte code.

Values and variables

var myName = “Ief”
myName: String = Ief

As you can see, it is not mandatory to define a type. Still Scala is strongly typed and knows that it is a String. Strongly typed means that you don’t need to define types a lot. Confused?

val myName = “Ief”

is the same as

 val myName : String = “Ief” 

Once the type of a variable or value is assigned you don’t need to repeat it again. Val represent a value, a final variable named ‘name’ of the type Sting with only an accesor method (getter).

var myName = “Ief”

Is a variable named name of the type String with an accesor method (getter) and a mutator method (setter)

Classes

A class Person with a variable name and a value surname would look like this in Scala

 class Person(var name : String, val surname : String) 

While the java counterpart would look like this

public class Person {
  private String name;
  private final String surname;

  public Person(final String surname) {
    this.surname = surname;
  }

  public String getName();
    return name;
  }

  public void setName(final String name) {
    this.name = name;
  }

  public String getSurname();
    return surname;
  }
}

You can instantiate the class using the following code

val me = new Person(“Ief”, “Cuynen”)
me: Person = Person@4d826d77

me.name
res7: String = Ief

me.name = “Jef”
me.name: String = Jef

me.surname
res8: String = Cuynen

me.surname = "Peeters"
res9: error: reassignment to val

You probably noticed that for zero argument methods you can skip the ( ) Scala is packed with syntactic sugar. A few more examples:

Regular expressions can be created just by calling the r method on a String

val regularExpression = “[0-9][a-Z]”.r

A Range of numbers from 1 to 10

1 to 10
res11: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

Functions

Functions are defined using the def keyword. Every function returns the value of the last statement of the function, even without an explicit return statement. It is even possible to return a new function as return value.

def addOne(x: Int): Int = x +1
addOne: (x: Int)Int

addOne(2)
res12: Int = 3

In scala it is also possible to return multiple values in 1 go by using tuples. Tuples are a way to group different values of different types into a single container without creating an explicit class.

def printStuff(x : Int): (Int, String)  = (x, "Hello number " + x)
printStuff: (x: Int)(Int, String)

printStuff(1)
res13: (Int, String) = (1,Hello number 1)

Functions can be used as arguments for other functions. This way it is possible to add behaviour.

def isEven(x : Int): Boolean =  x % 2 == 0
def isUneven(x : Int): Boolean = x % 2 == 1

(1 to 10).filter(isEven(_))
res20: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10)

(1 to 10).filter(isUneven(_))
res21: scala.collection.immutable.IndexedSeq[Int] = Vector(1, 3, 5, 7, 9)

Using functions as arguments greatly reduce the need for subclassing. Normally a subclass is used to ‘bind’ different behaviour to the same interface. By using functions as arguments, the behaviour is injected into interface.

Functions can be even combined into other functions which are called high order functions.

Option

Using null values is FP and Scala is a very bad practice. When you think about it, null values are pure evil in any programming for that matter. They cause unwanted side effects and you need to always check for null values to prevent NullPointerExceptions. Within Scala you can use the Option counterpart which is a decent way to solve the null evilness.

scala> def convertToInt(x: String): Option[Int] = {
     |    try {
     |        Some(Integer.parseInt(x))
     |     } catch {
     |        case e: Exception => None
     |    }
     | }
convertToInt: (x: String)Option[Int]

This function parses a String to an Int. In case the String can be successfully parsed, the Int value is returned (Some). In case an exception is thrown, None is returned

scala> convertToInt("1")
res22: Option[Int] = Some(1)
scala> convertToInt("abc")
res23: Option[Int] = None

To get the actual value, the getOrElse function can be called on the Option.

scala> val x = convertToInt("1").getOrElse(0)
x: Int = 1
scala> val x = convertToInt("abc").getOrElse(0)
x: Int = 0

Another way to get the value of the Option is to use a matcher.

scala> convertToInt("1") match {
     |     case Some(x) => println(x)
     |     case None => println("That String was not really an Int was it?")
     | }
1

scala> convertToInt("abc") match {
     |     case Some(x) => println(x)
     |     case None => println("That String was not really an Int was it?")
     | }
That String was not really an Int was it?

Pattern matching

You already saw above what you can do with a matcher. Look at it as the Java switch on steroids. It can match about any everything.

scala> def matchThis(x : Any) = x match {
     |     case 1 => println(1)
     |     case s : String => println("Match String " + s)
     |     case _ => println("whatever")
     | }
matchThis: (x: Any)Unit

scala> matchThis(1)
1

scala> matchThis("abc")
Match String abc

scala> matchThis(true)
whatever

Caveats

One of the caveats is that the java compiler does not compile scala and the scala compiler does not compile java. So 2-way dependencies probably lead to a big headache.

5 Minute JavaScript #19: Polyfills

The past few weeks were dedicated to the useful array methods. However these methods have been implemented in ECMAScript 5 and are therefore not available in older browsers such as IE8 and sometimes we have to support legacy browsers.

In JavaScript, we use polyfills to create behavior that is not implemented in browser. We can use polyfills to add every kind of behaviour to our application and a lot of websites provide these polyfills.

Basically what happens is that we first do a feature detection. Is the feature available in the browser? For example, does Array.prototype.map exist? Yes? That’s great! It means the feature has been implemented and is probably faster than every polyfill that we could come up with. Is it not available? Too bad, but we can create the Array.prototype.map method ourselves.

The Mozilla Developer Network has some of the most robust polyfills that are still fast in use. It also has an excellent documentation about the array methods. Here’s the page for the map functionality.

Using a polyfill doesn’t change the way the method is being called. If your browser does not support the map-method and you use a polyfill, you will still use it like this: [1, 2, 3].map(…); This is useful, because you don’t have to change syntax for different browsers.

Another solution is to use a framework that has implemented these functionalities. One of my favourites is underscore. This framework adds more useful methods than just the array methods to your function toolbelt.

framework adds more useful methods than just the array methods to your function toolbelt.

5 Minute JavaScript #18: reduce

The past weeks we dived in the wonderful world of array methods. Previously we already discussed forEach, filter, some and every, and map. Today we’ll take a look at the reduce method. While being extremely useful, its concept can be hard to grasp.

Also known as fold (in this case foldLeft) in other functional programming languages, reduce kan be used to combine all elements of an array into one single return value. That return value can be anything. It could be an array (then the reduce functions as a filter/map), but it can also be: an object, string, number, boolean… Everything is possible.

A simple example can be to use the reduce method for calculating a sum. Here’s the code how we would write it in any other imperative language.

var numbers = [1, 2, 3];
var sum = 0;
for (var i = 0; i < numbers.length; i++) {
	sum += numbers[i];
}

We can rewrite this code as follows using the reduce method

var sum = numbers.reduce(function (prev, cur) { return prev + cur; });

The reduce callback function takes two important parameters (prev, cur in this case). First of all we have the previous value. This is the value that got returned in the previous callback function. The current parameter is the current item in the list.

You might get your head around this functionality, but it’s not really useful in real applications. Its real strength lies in the fact that you can press a lot of elements together into one single return value. A use case for reduce might be this:

var user = { id: 'UUID', version: 0 };
var users = [/* list of users */];
var idVersionMap = users.reduce(function (map, user){ 
    map[user.id] = user.version; 
    return map; 
}, {});

In our blogpost about the map method we used map to create a new list of objects (with id and version). Here, we use the reduce method to create a single object that acts as a map with key = id and value = version. The empty {} that we passed along in the reduce callback function is the initial value the method needs to use.

5 Minute JavaScript #17: some and every

In the previous blogpost we discussed the map method on arrays in JavaScript. We still have some useful methods the go. Next in line are the some and every methods. These methods are similar and can be very useful when validating data.

var isEven = function (n) { return n % 2 === 0 };
var areAllEven = [2, 4, 6].every(isEven);
var someEven = [1, 2, 3].some(isEven);

The every method will check if for every element in the list, the callback functions returns true. If there is one single item in the array that returns false, the every method will return false as well. The some method is satisfied when there is at least one element in the array where the callback returns true.

var stockItem = { hasBeenShipped: true };
var selection = [/* list of stock items selected in a list */];
var hasNotBeenShipped = function (si) { return !si.hasBeenShipped };
var hasBeenShipped = function (si) { return si.hasBeenShipped };

$('#sendStockItems').attr('disabled', selection.every(hasNotBeenShipped));
$('#sendStockItems').attr('disabled', selection.some(hasBeenShipped));

The example here will disable a button when the selection in the list contains one or more items that already have been shipped. This code is very readable and concise. You can almost read exactly what it does: set attribute disabled when selection has some items that hasBeenShipped.

5 Things I wish I knew about APEX when I just started (part 3)

In my previous post of this series, I talked about cookie sharing in APEX. The next post in this series is about build options, I hope you enjoy it.

Build Options

Imagine having to release an apex application, but you don’t want some parts released in to the production environment yet, because they are unfinished, or not tested. Or you want to disable a module in your application for some reason.

Apex provides a solution for this called build options.

You can find the build options under shared components > logic > build options

Let’s create 2 build options:

The first one will keep the component active in our development environment, but will disable it on export so the developed content is disabled in our production environment.

buildoptions1

The second one will disable content in the application, and take over this behavior on export to our production environment.

buildoptions2

For the status there are two options possible:

Exclude, will disable the content in the current application, and include will keep it enabled in the current application.

For the default on export there are 3 possible combinations:

Same as current will take over whatever has been chosen in status when exporting a page. Exclude will disable the components on export of the application. Include will enable the components on export of the application.

Build options can be attached to any component in apex: pages, processes, regions, items, and can be found under the configuration tab when editing the components.

buildoptions3

As a test you can put the 2 build options on some page items in your current application.

When you run the page you will notice that in your development environment, one item will be visible and one will be gone from the page.

When you take an export and import it back in the new environment you will notice both items are removed from the page.

That’s it! The fourth blog in this series will be about recovering applications and page elements using flashback, and will be online soon.

OGh APEX World 2015

DSC_9284-001 (800x533)

iAdvise Diamond Sponser APEX World 2015

After 5 successful earlier editions of the APEX World day, they chose a different venue for the 2015 edition. The ship SS Rotterdam was the setting for the annual APEX World event. For us, it was not only the location that was special, we were also official Diamond Sponsor of APEX World 2015! And a great day it was! Not only to meet a lot of nice people from the Benelux APEX community, but also for the great sessions that have provided us with a lot of inspiration for the upcoming period. It was really an honour for us to be the Diamond Sponsor this year.

 

Like previous years, the day started with a short opening. This year, Reinier van Grieken, vice president and managing director of Oracle Netherlands was invited to do the opening. He emphasized that the OGh did a great job by welcoming such an enormous audience, which continued to grow over the past 5 years (more than 400 visitors this year).

In this overview we will take you aboard the SS Rotterdam on the 25th of March, so if you missed it, you’ll still get the highlights. And if you were there, you can look back on a great day.

 

Keynote: OraEvents – Stijn van Raes (iAdvise) & Yves van Looy (Oracle Belgium)

Stijn van Raes at APEX World 2015

Stijn van Raes at APEX World 2015

In an entertaining presentation the speakers told us about how Oracle and iAdvise created the situation of a supplier – customer – supplier – customer. iAdvise was hired to build the OraEvents application for Oracle (www.oraevents.eu). The architecture of this application makes it possible to collect data about the interests of registered users. In some situations this can be a huge advantage. For example, there was a situation when Oracle organized an event but it was really hard to get enough attendees. Oracle Belgium searched in the database of OraEvents and in half an hour they filled up the event.

At the end of this keynote, iAdvise wondered what could be possible features in future APEX versions (like  APEX 6, APEX 7 or even later). Thoughts about single page web applications, Node.js integration and Source Control were brought to attention. iAdvise hopes that the APEX community will think about these possible features and bring over these ideas on  https://apex.oracle.com/vote or the newly formed linkedin group http://goo.gl/L9DirJ

 

APEX suitable for high volume environments – PostNL & Fiton

Fiton and PostNL developed an application to process postal orders in a very easy and quick manner. Not only national but also international orders can be handled with this system.

Basic and simple APEX functionality was used to enter barcodes in a system which looked like some kind of wizard. Only 4 APEX pages were developed, besides a login system. The application was based on Theme 13 in APEX. The part of the system that takes care of printing invoices was built as a Java applet. The philosophy of this client case was: “Less is more”. Keep your application as simple as possible.

 

Oracle Forms to Oracle Application Express migration – iAdvise (Yvonne van Dorst) and Robeco (William de Vries)

Robeco decided to migrate 7 applications which had been developed with Oracle Designer. These applications have to be compatible with at least an Oracle 11g database and will need to have a distinct corporate identity. APEX turned out to be the best tool. In the beginning Robeco and iAdvise started to migrate 3 applications with the intention of migrating 4 more applications in the future. For Robeco it was very important to use one template for all applications. This could be realized by an APEX theme developed by iAdvise based on bootstrap in combination with a JavaScript framework.
All 7 APEX applications were developed in a period of 3 months. The business has become APEX minded and almost all questions are more or less like: “Can we do this in APEX?” The answer in most cases is: “Yes we can!” Robeco is a very satisfied APEX customer.

 

Design of good-looking, flexible and responsive applications – iAdvise (Menno Hoogendijk) and Twinq (Laurens Hamelink)

Twinq develops software for co-operations of owners of apartments. People who use this software will do this on several devices like a desktop (24 inch), a tablet (10 inch) or smartphone (5 inch). Twinq’s vision is that software has to be sexy and good-looking. To make this kind of software for all types of devices, iAdvise and Twinq used bootstrap. The APEX application uses AJAX and javascript, but all in favor of usability. Besides this, the applications are equipped with the possibility to use keyboard shortcuts.

At the end of this presentation, the audience was asked to visit an online vote, just like tinder. They could indicate whether they really experienced the demo as “Sexy Software” or not. More than 80% was convinced of the sexiness of the software.

 

Hidden Nuggets in Application Express 5.0 Page Designer – David Peake (Oracle US)

Everyone knows that APEX 5.0 has a lot in store for us. In this presentation, David Peake took
us through the new page designer and told us his favorite features.

The page designer is now divided in three sections. The old tree view can be consulted on the left side of the screen.

The middle section consists of a wide grid layout where we can easily drag and drop new items to our page. Messages will show you what is missing for the new created items.

In the right section we can directly see and edit the properties of the selected item. This new interface allows us to develop much more efficiently. Besides editing one item at a time, it is now possible to edit multiple items. This will save us a lot of time, for example when you want to change the template of all your labels. And when the latest adjustment to your page does not meet your expectations, you can now undo and redo it by simply pressing a button.

Not only the grid layout is quite convenient, keyboard shortcuts will soon be our best developing buddies. To help us along the way, help texts and search capabilities have been increased considerably. Now we will lose less time, if we are looking for that one particular item.

The page designer will give us the possibility to develop even faster!

 

Interactive Reports: Watch out for the Pitfalls! – Peter Raganitsch (FOEX (AT))

In APEX, we’ve got two different report types to work with: Classic and interactive reports. Many developers prefer the interactive report, because the user can change the appearance of the data through several manipulations. This means that the query behind this report is also adjusted. To figure out how the query will look like after a few filters, you can use the debug function. To get the full query available in logging, you must replace the ‘YES’ with ‘LEVEL9’ in the url. This gives you a more detailed logging. You can also add a small PL/SQL code in the application properties (Security, Database Session, Initialization PL/SQL code):
“APEX_DEBUG.enable (9) ;”. Remember after testing to remove it again.

The pagination type also affects the query of your report. If you use the type ‘X to Y of Z’, then the query will be extended to return the total number of rows. Therefore, use the type ‘X to Y’ for reports with many records.

Also, there is a very useful package for interactive reports named APEX_IR. This can be used to see the full runtime query of your interactive reports, add filters, clear or reset the report settings, delete saved reports and manage subscriptions.

Version 5.0 has several enhancements on interactive reports. Henceforth, it will be possible to use multiple interactive reports per page. Besides that, the action region – after selecting an option in the action menu – will be showed in modal dialogs instead of above the report. The menu is also expanded with the pivot function and the end user can now do a group by on a maximum of eight fields instead of five. With all these improvements, version 5.0 will be very well received by both, developer and end user.

 

A Spotlight on the Smaller Features of APEX 5 – Dietmar Aust (Opal Consulting (DE))

After three early adopters and a pre-production version of APEX 5, everyone nowadays knows about the most important and biggest new features of APEX 5. But what about those features you don’t notice immediately? Dietmar Aust took us through some of those features during his session about the smaller features of APEX 5.

One of the functional improvements Dietmar told us about is: the file storage. In the past apex versions there were no relative file paths, you had to upload your files individually and updating your files took a lot of time. In the new file storage you do have relative file paths and there is the possibility to upload zip files that will be extracted into the correct folders. Updating your files can be done this way too. Also after updating your files you’ll notice at runtime that the version number, which you can find in the url referencing your files has changed to avoid caching issues.

Another runtime engine improvement is the extended substitution syntax where you can now define different escaping modes. For example: if you use a dynamic action that creates a JavaScript alert to show an application item like ‘&P1_ITEM.’. In this case, cross site scripting can be applied. To avoid this there is now the possibility to escape JS syntax by defining the application item like this: ‘&P1_ITEM!JS.’.  There are a few more escaping options that can be used. These can be found in the slides that you can download from Dietmar Aust’s blog (http://daust.blogspot.be/2015/03/slides-from-my-presentation-at-apex.html) like all other improvements that have been discussed in the session.

 

Keynote: Elegance in the Enterprise – Shakeeb Rahman (Oracle US)

On every project I’ll try to surpass my previous creations in usability and design. And every time I’ll spend some time analyzing the most popular websites about their latest user interfaces and the way they interact with the end user. How do they present their navigation? Where do they put the buttons? And how do they organize their content on a page? All these questions are important because you want your users to feel comfortable when they use your application.

This keynote felt like a spring breeze on the – maybe a little bit – too hot SS Rotterdam. It was refreshing to see the amount of dedication, consideration and research the APEX design development team put in their Universal Theme. Shakeeb Rahman brought a lot of liberating facts about the way users interact with web applications to our attention. One of the statements that caught my attention was:

Most users put a higher rate on an application after the design is improved because they believe it works better than the old one.

Shakeeb also told us to think twice before using reports. Because in some cases it may not be the best approach for presenting the data to the end user. Sometimes it’s more efficient to use a diagram or a chart because users instantly see how your data it related. And if using a report still is the best approach, try to eliminate the columns users don’t really need to see right away. Minimizing the amount of data on a screen results in faster reading and, in that way, is more efficient.

Another thing to reflect on when building your application, is to split the contents into smaller bits by grouping similar fields. By dividing your contents, users don’t see your page as a big chunk of data,  but more like smalls pieces of useful information.

The new built-in template that comes with APEX 5 results in easy-to-create, smart, responsive web applications because APEX has done the research for you. It uses built-in crisp icons and follows the currently hot “flat design trend”. Now it’s not only faster to create user friendly web application it’s also much easier because they put all the know-how about user interaction in the new and improved application builder.

That’s also handy because now you can take a peek at how APEX pages are designed if you’re looking for inspiration instead of googling around the web like I used to do before.

iAdvise consultant at APEX World 2015

iAdvise consultant at APEX World 2015

Java 8 and Spring 4

On March 27, 2014, the Spring community was happy to announce the Spring Framework 4.0.3. The reason why is that it was the first release of the Spring Framework with Java 8 support. Since then, the Spring team worked very hard to provide major updates for the Spring Framework to be even more supportive towards Java 8. As of September 4, 2014, the Spring Framework 4.1 has arrived with even more support towards the Java community.

Lambda support in Spring 4.0

A good example to show the Lambda support in Spring is the JdbcTemplate class. If we would like to obtain female employees and map them as an instance of type Employee, we could do something like this:

JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);

jdbcTemplate.query("SELECT first_name, last_name FROM employee WHERE gender = ?",
                   ps -> {ps.setString(1, "FEMALE");},
                   (rs) -> new Employee(rs.getString(1), rs.getString(2)));

The complete list of Spring 4.0 features can be found here.

Optional for injection points and MVC handler parameters in Spring 4.1

As of Spring 4.1, JDK 1.8’s java.util.Optional is now supported for @RequestParam, @RequestHeader, and @MatrixVariable controller method arguments. This means that while using Java’s Optional, you make sure that parameters are never null.

The following example shows an example of a @RequestParam in Spring MVC prior to version 4.1.

@RequestMapping(value="/iadvise")
public String findEmployee(@RequestParam(value = "employeeId") String employeeId) {
  StringBuilder response = new StringBuilder("id: ");
  response.append(employeeId.toUpperCase());
  return response.toString();
}

When calling the findEmployee method without providing an employeeId, the method will return a NullPointerException. This can be solved by Java’s Optional element.

@RequestMapping(value="/iadvise")
public String findEmployee(
  @RequestParam(value = "employeeId") Optional<String> employeeId){
  StringBuilder response = new StringBuilder("id: ");
  employeeId.ifPresent(value -> response.append(employeeId.toUpperCase()));
  return response.toString();
}

The same result can be achieved for the @RequestHeader, and @MatrixVariable annotations.

The complete list of Spring 4.1 features can be found here.