Menu
I'm using the cats lib for this.
It's easy enough to combine two lists using their applicative functor instance (or Cartesian, to be precise):
import cats._
import cats.implicits._
(List(23, 4), List(55, 56)).mapN(_ + _)
>> List(78, 79, 59, 60)
However, I can't seem to be able to do the same with two functions:
val strLength: String => Int = _.length
(strLength, strLength).mapN(_ + _)
>> value mapN is not a member of (String => Int, String => Int)
It does work if I do some of the implicit conversions explicitly, and if I create a type alias to give the compiler a hand:
type F[A] = Function1[String, A]
val doubleStrLength = catsSyntaxTuple2Cartesian[F, Int, Int]((strLength, strLength)).mapN(_ + _)
doubleStrLength("hello")
>> 10
Is there an easier way to do this? Seems excessively verbose
Edit: I create a worksheet here if you wanna play with it: https://scastie.scala-lang.org/dcastro/QhnD8gwEQEyfnr14g34d9g/2
748
Functors apply a function to a wrapped value: Applicatives apply a wrapped function to a wrapped value: Monads apply a function that returns a wrapped value to a wrapped value. Monads have a function >>= (pronounced "bind") to do this.
In functional programming, a functor is a design pattern inspired by the definition from category theory, that allows for a generic type to apply a function inside without changing the structure of the generic type. Simple examples of this are Option and collection types.
Applicative functors are the programming equivalent of lax monoidal functors with tensorial strength in category theory. Applicative functors were introduced in 2008 by Conor McBride and Ross Paterson in their paper Applicative programming with effects.
Functor in Haskell is a typeclass that provides two methods – fmap and (<$) – for structure-preserving transformations. To implement a Functor instance for a data type, you need to provide a type-specific implementation of fmap – the function we already covered.
This only works if you have partial-unification enabled.
The easiest way to do so, is to add the sbt-partial-unification plugin.
If you're on Scala 2.11.9 or newer, you can also simply add the compiler flag:
scalacOptions += "-Ypartial-unification"
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
