Functors, Applicatives and Monads In Scala
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Transcript of Functors, Applicatives and Monads In Scala
Functors,Applicatives and Monads
Pallavi SinghSoftware ConsultantKnoldus Software LLP
Objectives:
Functors
Applicatives
Monads
Demo
Problem :
We have a simple value
We apply a function to it
Lets extend it , the value can be in a context,Now when we apply a functionto this value,we get results depending on the context.
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
FunctorsWhen a value is wrapped in a context, you cant apply a normal function to the value.We need a map. The map knows how to apply functions to values that are wrapped in a context.
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Functors
Definition : Functor is a type class. A Functor is any data type that defines how map applies to it.
Speaking in-formally you apply a function to a wrapped value using map. The map knows how to apply the function.
Functors
We have a Constructor C[_] and two types A and B,we want to apply functions of type C[A]=>C[B], so we need adequate transformations
( A=>B ) => ( C[A]=>C[B] )
And we need to define a map
def map[A,B](A=>B):(F[A]=>F[B] )
Functors
Example: Options , Streams
Object OptionFunctor extends Functor[Option] { def map[A, B](f: A B): Option[A] Option[B] = option option map f }
Problem :Given a function
what happens when you apply a function to another function , we have another function.
Functions are functors too ! A map on a function is function composition.
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Problem :
We have a value wrapped in context
And functions are wrapped in a context too!
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
ApplicativesWhen a value and function both are wrapped in a context. We cant apply it as we apply a simple function. We need an apply. It knows how to apply a function wrapped in a context to a value wrapped in a context.
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Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Applicatives
Def : Applicative is typeclass. Applicative is any data type that defines how apply applies to it.
Apply takes a functor that has a function in it and another functor and extracts that function from the first functor and then maps it over the second one.
Speaking in-formally you apply a function wrapped in context to a value wrapped in context.
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Applicatives
We have a Constructor C[_] and two types A and B, we want to apply functions of type C[A]=>C[B],so we need adequate transformations
(C[A=>B] ) => ( C[A]=>C[B] )
And we need to define a apply
def apply[A,B](F[A=>B]):(F[A]=>F[B] )
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Problem :Given a function
what happens if we feed it awrapped value?
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Monads
Monads apply a function that returns a wrapped value to a wrapped value.
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Image Source : http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
Monads
Definition: Monad is a type class. A monad is a data type that implements the flatMap.
Speaking in-formally you apply a function that returns a wrapped value, to a wrapped value.
Monads
We have a Constructor C[_] and two types A and B,we want to apply functions of type C[A]=>C[B],so we need adequate transformations
( A=>C[B] ) => ( C[A]=>C[B] )
And we need to define a flatMap
def flatMap[A,B](A=>F[B]):(F[A]=>F[B] )
Monads
Example: List , Set , Option and Future all are Monads
Future is a wrapper over some asynchronous operation. Once the future has been completed you can do whatever it is you need to do with its result.
Difference b/w Monad and Monoids ?
Monoid : Given a type T, a binary operation Op:(T,T)=>T and instance Zero:T then the triple(T, Op , Zero) is called a Monoid if it has the following properties: Neutral Element and Associativity.
Monad instance simply wraps the value of type A within the given context and expose a certain set of methods to operate on them,
Monoid instance already knows how to combine these values of type A within the given context.
Are Monads powerful than Applicatives?
Applicatives and monads both model running computations in sequence. But Monads are more powerful because with applicatives you can sequence the computations, but monads allow you to sequence computations with the additional property that the result of subsequent computations can depend on the result of previous computation.
Demo
https://github.com/knoldus/functors-applicatives-monads
Questions
References
http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
http://www.smartjava.org/content/scalaz-features-everyday-usage-part-1-typeclasses-and-scala-extensions
http://eed3si9n.com/learning-scalaz/Applicative.html
https://thedet.wordpress.com/2013/02/11/functors-in-images/
https://thedet.wordpress.com/2012/05/20/functors-monads-applicatives-playing-with-map-functor/
Thank You