Palindrome in Haskell

This is probably a week after i started to read Haskell (a functional programming language). Having tried few examples from the book and writing few on my own, i feel like it is a different world. If i m successful enough to keep my interest with Haskell and continue to practice, i think it is going to improve my thinking at a very least. I m not so sure of using this language at work (but who knows). More on Haskell later.

Here is the code that says a given String (list) is palindrome. (see, how expressive Haskell (FP) is). The first two line is to reverse the list and the last line is the one that decides whether or not the original and reversed string same (you need to write probably 10 lines in imperative language)

rev [] = [] 

rev (x:xs) = reverse xs ++ [x] 

palindrome x = (x == rev x)

 Here is the sample output (from WinGHCi)

*Main> palindrome "test"
False
*Main> palindrome "madam"
True
*Main> palindrome "123321"
True
*Main> palindrome [1..100]
False
*Main> palindrome "a great good haskell"
False
*Main> 

You can find my Haskell notebook (and my daily progress) here. (thanks to Dropbox)

First Program in Haskell

Recently, I stumbled upon a new programming paradigm - functional programming. Rather than focusing on variables, we define functions that does something. Without much of theory, let us quickly see an example

Write a program that finds triplets (a, b c) such that a, b and c are sides of a right angle triangle with none of the sides is greater than 20. I tried to write programs in Java and in Haskell as well. Here is the code snippet

Java

public class RightAngleTuples {

public static void main(String[] args) {

printTuples();

}

public static void printTuples() {

for(int c = 1; c <= 10; c++) {

for(int a = 1; a <= c; a++) {

for(int b = 1; b <= a; ++b ) {

if(a*a + b*b == c*c && a+b+c == 24) {

System.out.println(a + ", " + b + ", " + c);

}

}

}

}

}

}

Haskell

 Prelude> let triples = [(a,b,c) | c <- [1..10], a <- [1..c], b <- [1..a], a^2 + b^2 == c^2, a+b+c == 24 ]

Prelude> triples

[(8,6,10)]

Initially it may appear that both the programs are different syntactically. But if you really see, while programming in an imperative languages, we need to think a lot of logic and variables (or memory location) that maintains the state of the program. It is programmers responsibility to keep the state sane. But in the case of functional programming, there is no concept of state. Everything is functions (obviously everything is logic).

If you are really interested to learn a new programming paradigm, i recommend Haskell. With my few hours of encounter with Haskell, i feel it changes one's thinking :-) and Learn you a Haskell for Great Good by Miran Lipovaca can be a great resource. (BTW, i copied the above example from the book and i promise that it is in fact last example that i will steal from the book). An heads-up: reading Haskell doesn't increase your value in job market :-), you cannot ask for 40% more hike but just improves your geeky quotient :-)

More stuffs on Haskell in coming weeks/months. Sharing never hurts :-)