Sunday, November 15, 2015

while ((line = readLine()) != "") doesn't work in Scala

In C++ or Java, line = readLine() would return the line itself, however, in Scala, assignment to var type variable returns () i.e. Unit, so it cannot be compared to "" in a while loop.

Pure functional languages do not have loops because of this same reason, it does not return anything

Friday, November 13, 2015

Scala Class and Object

class checksumAccumulator {

private var sum = 0

def add(b: Byte): Unit = {
sum += b

def checksum(): Int = {
~(sum & 0xFF) + 1


By default sum is public, we have to explicitly make it private.
Parameter b is by default val, so we cannot re-initialize it in checksum method, there is no return keyword, in such case, last value computed by method is returned - this is the recommended style - avoid explicit and multiple return statements

class ChecksumAccumulator {
private var sum = 0
def add(b: Byte) { sum += b }
def checksum(): Int = ~(sum & 0xFF) + 1

since our methods are just single statements, they can be written without {}, also when method does not return anything, i.e. its return type is Unit, we can skip writing the return type and "=", like in the add method

all datatypes can get converted to Unit - it simply looses the data
semicolon at the end of the statement are optional

object ChecksumAccumulator {

defining object instead of class gives singleton of the class called companion object class
A class and its companion object can access each other’s private members.

To run a Scala program, you must supply the name of a standalone singleton object with a main method that takes one parameter, an Array[String], and has a result type of Unit. Any singleton object with a main method of the proper signature can be used as the entry point into an application.

object Summer {
def main(args: Array[String]) {

We can also write the following:

object FallWinterSpringSummer extends Application {

Thursday, November 12, 2015

Who uses functional programming

  • Erlang
    • Amazon
    • Yahoo
    • Facebook
    • Whatsapp
  • Haskell
    • AT&T
    • Google
    • Facebook
    • NVIDIA
    • Banks - ABN Amro, BoA, Barclay, Credit Suisse, Deutche Bank, SC
  • OCaml
    • Facebook
    • Bloomberg
  • Scala
    • LinkedIn
    • Twitter
    • Sony
    • Seimens
  • Clojure
    • Facebook
    • Walmart
    • Citi

Why functional programming matters now

  • Clock speed of processors are not increasing
  • Cores on a processor are increasing
  • In future we may have hundreds of cores
    • Execution is no longer the bottleneck
    • Memory is a bottleneck
  • Foo(f(x), f(x))
    • both f(x) might get executed on different cores
    • it will not matter if there is no state change
      • Hence functional programming

Functional Programming principles

Functional programming has 2 principles:

  • Functions are first class values
    • pass them as parameter
    • return them from a function
    • store them in variable
    • define function inside a function
    • have function literals in the code - like int lieral 42 => anon function
  • Operations should map input values to output
    • Not change data in place - like what OO does
    • Makes data immutable
    • No side-effects => referentially transparent

Attended conference on functional programming

Attended a conference ( on functional programming.
It gave me the push needed to take up learning a new language. I have started exploring SCALA, I will be posing my learning here.

I am the one in white shirt

Sunday, April 05, 2015

My other blogs - I have decided to give a lot of attention to MongoDB, this new blog will have posts about my experience and experiments with it.