Scala {Monad}

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Scala USAGE

Today’s Talk

•Monads in Scala Standard Library

•How to use them

Monad?

•Effects on a value •Structure that represents computations defined as sequences of steps

Monad?

•Effects on a value:unit

•Structure that represents computations defined as sequences of steps:flatMap

Effects on a value• VALUE • MONAD(VALUE) • Option(VALUE),List(VALUE),Try(VALUE),Future(VALUE)

Sequencial Computations

• X -> Y -> Z • M[X] -> M[Y] -> M[Z]

f g

f’ g’

Behaviour• f = X => M[Y]g = Y => M[Z]

• X -> M[X] -> M[Y]

• M[Y] -> M[Z] -> …

unit flatMap

flatMap flatMap

Simple User DAO

Option

Effects on a

Nullable Value

(Some or None)

Unit

FlatMap

Effects on a Nullable Value

Some(User) or None

Exception Safety?

Try

Effects on a

Throwable Value

(Success or Failure)

Unit

FlatMap

Effects on a Nullable & Throwable Value

Success(Some(User)) orSuccess(None) or

Failure(throwable)

Blocking Thread?

Future

Effects on a

Blocking Value

(Success or Failure)

Unit

FlatMap

Effects on a Nullable & Throwable Valuein Asynchronously

Success(Some(User)) orSuccess(None) or

Failure(throwable)

List

Effects on

Iterable Values

(List or Nil)

Monad Laws

• Left Identity • Right Identity • Associativity

Pull a value out of Monad

•Helper Functions:getOrElse,fold,foreach,recover…

•Pattern Match •3rd Party Library:Akka,Spray…

Akka

Spray

Benefits

• Keep your codes CLEAN

• Easy To Guess(READABLE)

• MAINTAINABLE

• Less Code Less BUGS

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Thanks

han_sangwon@cyberagent.co.jp