meow/meow.control/Applicative

Applicative

trait Applicative[F[_]]

A functor with application, providing operations to

  • embed pure expressions ('pure'), and
  • sequence computations and combine their results ('<*>' and 'liftA2').

A minimal complete definition must include implementations of 'pure' and 'liftA2'.

Further, any definition must satisfy the following:

Identity

pure[F](identity) <*> fa == fa



Composition


pure[F](compose) <*> fa <*> fb <*> fc == fa <*> (fb <*> fc)



Homomorphism


pure[F](f) <*> pure(x) == (pure[F](f(x)))



Interchange


u <*> pure(y) == pure[F]((f: String => String) => f(y)) <*> u



Companion
object
class Object
trait Matchable
class Any
Value members
Abstract methods
 def liftA2[A, B, C](f: A => B => C): F[A] => F[B] => F[C]
Lift a binary function to actions.


Lift a binary function to actions.


Example
val f = (x: Int) => (y: Int) => x + y
val ff = liftA2[Option](f)
ff(Option(1), Option(2)) == Option(3)



 def pure[A](a: A): F[A]
Lift a value.


Lift a value.


Example
pure[Option](1) == Option(1)
(pure(1): Option[Int]) == Option(1)



Extensions
Extensions
extension (fa: F[A])
@targetName("productRight") 
 def *>[A, B](fb: F[B]): F[B]
Sequence actions, discarding the value of the first argument.


Sequence actions, discarding the value of the first argument.


Example
Option(1) *> Option(2) <* Option(3) == Option(2)



@targetName("productLeft") 
 def <*[A, B](fb: F[B]): F[A]
Sequence actions, discarding the value of the second argument.


Sequence actions, discarding the value of the second argument.


Example
Option(1) *> Option(2) <* Option(3) == Option(2)



@targetName("apFlipped") 
 def <**>[A, B](fab: F[A => B]): F[B]
Flipped version of this.ap


Flipped version of this.ap


inline def unless[A, B](cond: Boolean): F[Unit]
Conditional execution of 'Applicative' expressions.


Conditional execution of 'Applicative' expressions.


Example
 doSomething.unless(condFailed) 



inline def when[A, B](cond: Boolean): F[Unit]
Conditional execution of 'Applicative' expressions.


Conditional execution of 'Applicative' expressions.


Example
 doSomething.when(cond) 



extension (fab: F[A => B])
@targetName("ap") 
 def <*>[A, B](fa: F[A]): F[B]
Sequential application.


Sequential application.


Example
val f = (x: Int) => (y: Int) => x + y
f `<$>` Option(1) <*> Option(2) == Option(3)