What a Java guy can learn from Haskell??

Tomasz Nurkiewicz

nurkiewicz.com | nurkiewicz@gmail.com | @tnurkiewicz

I don't know Haskell

What Haskell doesn't have?

• null
• variables
• exceptions
• void
• Object
• loops
• method overloading
• side effects

Type system

Hoogle

[a] -> (a -> b) -> [b]       //map

[a] -> (a -> Bool) -> Bool   //all, any

Ord a => [a] -> [a]          //sort
					

Structural search

IntelliJ IDEA

class $Class$ {
	public static int $method$(String $string$, 
	                           int $def$)
}
					

The world chose

• Matz at RubyConf 2014: Will Ruby 3.0 Be Statically Typed?
• Guido van Rossum Wants to Bring Type Annotations to Python
• core.typed - an optional type system for Clojure
• PHP 5: Type Hinting, RFC: Return Type Declarations
• Facebook: Hack (składnia PHP, statyczne typowanie)
• JavaScript: Flow, TypeScript, Dart, GWT, Scala.js, Elm, Haste, purescript

Stringly typed

String             uuid;
String             website;
String             email;
String             firstName, lastName;
String             clientXml;
int                birthYear;
long               registrationDate;
int                min, max;
boolean            registered;
int                priority;
					

Strongly typed

UUID               uuid;
URL                website;
Email              email;
Name               name;
Optional<Document> client;
Year               birth;
Instant            registration;
Range<Integer>     range;
Status             status;
Priority           priority;
					

Living documentation

CompletableFuture<BigDecimal> doSomeWork() {
	//...
}
					

Try<InputStream> tryOpen(File f) {
	return Try.of(() ->
		new FileInputStream(f));
}
					

null

20 years of Java

50 years of null

Tony Hoare (2009)

"Java 8 in Action"

"These unlucky people have names that break computers"

www.bbc.com/future/story/20160325-the-names-that-break-computer-systems

Option(al)?

Optional<String> opt = null;  //YOLO
					

scala> Some(null) == None
res1: Boolean = false
					

Immutability

1994

Flyweight pattern

2013

value object - 258 times

immutable - 68 times

"Implementing DDD"

Linus Torvalds

git

Wolfenstein 3D (1992)

float Q_rsqrt( float number ) {
  long i;
  float x2, y;
  const float threehalfs = 1.5F;

  x2 = number * 0.5F;
  y  = number;
  i  = * ( long * ) &y;         // evil floating point 
                                // bit level hacking
  i  = 0x5f3759df - ( i >> 1 ); // what the fuck? 
  y  = * ( float * ) &i;
  y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration
//y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration,
                                              // this can be removed

  return y;
}					

Why?

• Saving game state
• Networking

Databases

• Cassandra
• HDFS
• Datomic

Summary

• null
• variables
• exceptions
• void
• Object
• loops
• method overloading
• side effects

Thank you!