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Implicit for Function not being found

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2

I have this typeclass

import simulacrum._
@typeclass trait Functor[F[_]] 
 def map[A, B](fa: F[A])(f: A => B) : F[B]
 def lift[A, B](fa: F[A])(f: A => B) : F[A] => F[B] = fa => map(fa)(f)
 def as[A, B](fa: F[A], b: => B) : F[B] = map(fa)(_ => b)
 def void[A](fa: F[A]) : F[Unit] = as(fa, ())

and this is the implementation

object Functor 
 implicit val listFunctor: Functor[List] = new Functor[List] 
 def map[A, B](fa: List[A])(f: A => B) = fa.map(f)
 
 implicit def functionFunctor[X]: Functor[X => ?] = new Functor[X => ?] 
 def map[A, B](fa : X => A)(f : A => B) = fa andThen f
 

I can easily discover the List implicit implementation as

object Chapter1 extends App 
 import Functor.ops._
 List(1, 2, 3).as("foo").foreach(println)

The above works perfectly fine. I can also do

object Chapter1 extends App 
 import Functor._
 val func : Int => String = implicitly[Functor[Int => ?]].map(_ + 2)(_.toString)
 println(func(5))

But when I try

object Chapter1 extends App 
 import Functor.ops._
 val x : Int => Int = _ + 2
 val y : Int => String = x.map(_.toString)

It doesn't find my implicit implementation and says that the value map is not a member of Int => Int

scala simulacrum

share|improve this question

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

add a comment | 

2

I have this typeclass

import simulacrum._
@typeclass trait Functor[F[_]] 
 def map[A, B](fa: F[A])(f: A => B) : F[B]
 def lift[A, B](fa: F[A])(f: A => B) : F[A] => F[B] = fa => map(fa)(f)
 def as[A, B](fa: F[A], b: => B) : F[B] = map(fa)(_ => b)
 def void[A](fa: F[A]) : F[Unit] = as(fa, ())

and this is the implementation

object Functor 
 implicit val listFunctor: Functor[List] = new Functor[List] 
 def map[A, B](fa: List[A])(f: A => B) = fa.map(f)
 
 implicit def functionFunctor[X]: Functor[X => ?] = new Functor[X => ?] 
 def map[A, B](fa : X => A)(f : A => B) = fa andThen f
 

I can easily discover the List implicit implementation as

object Chapter1 extends App 
 import Functor.ops._
 List(1, 2, 3).as("foo").foreach(println)

The above works perfectly fine. I can also do

object Chapter1 extends App 
 import Functor._
 val func : Int => String = implicitly[Functor[Int => ?]].map(_ + 2)(_.toString)
 println(func(5))

But when I try

object Chapter1 extends App 
 import Functor.ops._
 val x : Int => Int = _ + 2
 val y : Int => String = x.map(_.toString)

It doesn't find my implicit implementation and says that the value map is not a member of Int => Int

scala simulacrum

share|improve this question

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

add a comment | 

I have this typeclass

import simulacrum._
@typeclass trait Functor[F[_]] 
 def map[A, B](fa: F[A])(f: A => B) : F[B]
 def lift[A, B](fa: F[A])(f: A => B) : F[A] => F[B] = fa => map(fa)(f)
 def as[A, B](fa: F[A], b: => B) : F[B] = map(fa)(_ => b)
 def void[A](fa: F[A]) : F[Unit] = as(fa, ())

and this is the implementation

object Functor 
 implicit val listFunctor: Functor[List] = new Functor[List] 
 def map[A, B](fa: List[A])(f: A => B) = fa.map(f)
 
 implicit def functionFunctor[X]: Functor[X => ?] = new Functor[X => ?] 
 def map[A, B](fa : X => A)(f : A => B) = fa andThen f
 

I can easily discover the List implicit implementation as

object Chapter1 extends App 
 import Functor.ops._
 List(1, 2, 3).as("foo").foreach(println)

The above works perfectly fine. I can also do

object Chapter1 extends App 
 import Functor._
 val func : Int => String = implicitly[Functor[Int => ?]].map(_ + 2)(_.toString)
 println(func(5))

But when I try

object Chapter1 extends App 
 import Functor.ops._
 val x : Int => Int = _ + 2
 val y : Int => String = x.map(_.toString)

It doesn't find my implicit implementation and says that the value map is not a member of Int => Int

scala simulacrum

share|improve this question

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

import simulacrum._
@typeclass trait Functor[F[_]] 
 def map[A, B](fa: F[A])(f: A => B) : F[B]
 def lift[A, B](fa: F[A])(f: A => B) : F[A] => F[B] = fa => map(fa)(f)
 def as[A, B](fa: F[A], b: => B) : F[B] = map(fa)(_ => b)
 def void[A](fa: F[A]) : F[Unit] = as(fa, ())

object Functor 
 implicit val listFunctor: Functor[List] = new Functor[List] 
 def map[A, B](fa: List[A])(f: A => B) = fa.map(f)
 
 implicit def functionFunctor[X]: Functor[X => ?] = new Functor[X => ?] 
 def map[A, B](fa : X => A)(f : A => B) = fa andThen f
 

object Chapter1 extends App 
 import Functor.ops._
 List(1, 2, 3).as("foo").foreach(println)

object Chapter1 extends App 
 import Functor._
 val func : Int => String = implicitly[Functor[Int => ?]].map(_ + 2)(_.toString)
 println(func(5))

object Chapter1 extends App 
 import Functor.ops._
 val x : Int => Int = _ + 2
 val y : Int => String = x.map(_.toString)

share|improve this question

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

share|improve this question

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

asked Mar 24 at 21:36

Knows Not MuchKnows Not Much

11.4k29112227

1 Answer
1

active

oldest

votes

3

Compiler can't see that Int => Int is Int => ? applied to Int.

Add

scalacOptions += "-Ypartial-unification"

to build.sbt.

It's necessary for normal work with higher-kinded types with Cats, Scalaz or manually.

By the way, there's no sense to import Functor._

share|improve this answer

edited Mar 24 at 22:05

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Ahhh.... This is the 100th time partial unification has bit me
  
  – Knows Not Much
  Mar 24 at 22:11
  

  
  
  
  

add a comment | 

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3

Compiler can't see that Int => Int is Int => ? applied to Int.

Add

scalacOptions += "-Ypartial-unification"

to build.sbt.

It's necessary for normal work with higher-kinded types with Cats, Scalaz or manually.

By the way, there's no sense to import Functor._

share|improve this answer

edited Mar 24 at 22:05

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Ahhh.... This is the 100th time partial unification has bit me
  
  – Knows Not Much
  Mar 24 at 22:11
  

  
  
  
  

add a comment | 

3

Compiler can't see that Int => Int is Int => ? applied to Int.

Add

scalacOptions += "-Ypartial-unification"

to build.sbt.

It's necessary for normal work with higher-kinded types with Cats, Scalaz or manually.

By the way, there's no sense to import Functor._

share|improve this answer

edited Mar 24 at 22:05

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Ahhh.... This is the 100th time partial unification has bit me
  
  – Knows Not Much
  Mar 24 at 22:11
  

  
  
  
  

add a comment | 

Compiler can't see that Int => Int is Int => ? applied to Int.

Add

scalacOptions += "-Ypartial-unification"

to build.sbt.

It's necessary for normal work with higher-kinded types with Cats, Scalaz or manually.

By the way, there's no sense to import Functor._

share|improve this answer

edited Mar 24 at 22:05

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622

scalacOptions += "-Ypartial-unification"

share|improve this answer

edited Mar 24 at 22:05

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622

answered Mar 24 at 22:00

Dmytro MitinDmytro Mitin

12.1k1622