milessabin

[acyclic] --== Extracting dependencies for acyclic ==--
[acyclic] Fetching https://github.com/lihaoyi/acyclic.git
[acyclic] into /home/miles/projects/community-builds/clones-0.9.5/245e354ad2399f7a8e44b501df16710d5ca8e18e-acyclic
[acyclic] Took: 00h 00m 00.4s
[acyclic] Cloning /home/miles/projects/community-builds/clones-0.9.5/245e354ad2399f7a8e44b501df16710d5ca8e18e-acyclic
[acyclic] to /home/miles/projects/community-builds/target-0.9.5/extraction/d4f22467376ec652fb03d6c58593ba6d267adf39/projects/73e1fbbb9c28dd54a52679838829b3b71d4f9386
[acyclic] Took: 00h 00m 00.0s
[acyclic] Fetching /home/miles/projects/community-builds/clones-0.9.5/245e354ad2399f7a8e44b501df16710d5ca8e18e-acyclic
[acyclic] into /home/miles/projects/community-builds/target-0.9.5/extraction/d4f22467376ec652fb03d6c58593ba6d267adf39/projects/73e1fbbb9c28dd54a52679838829b3b71d4f9386
[acyclic] Took: 00h 00m 00.0s

milessabin

miles@tarski:shapeless (master)% sbt -Dsbt.profile=2.12.x                                                                                                                                                                                                                                                                     
[info] Loading global plugins from /home/miles/.sbt/0.13/plugins
[info] Loading project definition from /home/miles/projects/shapeless/project
[info] Set current project to root (in build file:/home/miles/projects/shapeless/)
> project coreJVM
[info] Set current project to core (in build file:/home/miles/projects/shapeless/)
> ++2.12.0-RC2
[info] Setting version to 2.12.0-RC2
[info] Reapplying settings...
[info] Set current project to core (in build file:/home/miles/projects/shapeless/)

milessabin

package demo

import scala.language.higherKinds
import scala.language.implicitConversions

trait Functor[F[_]] {
  def map[A, B](fa: F[A])(f: A => B): F[B]
}

trait Monad[F[_]] extends Functor[F] {

milessabin

import scala.language.higherKinds

trait Functor[F[_]] {
  def map[A, B](fa: F[A])(f: A => B): F[B]
}

trait Traverse[F[_]] {
  implicit val F: Functor[F]
}

milessabin

tapply: (a -> b) -> a -> b
tapply ab a = ab a

foo: (tapply List Nat) --OK
foo = [1, 2, 3]

mkPair: a -> b -> (a, b)
mkPair a b = (a, b)

bar: (mkPair Nat String) -- Not OK

milessabin

// Compiled with ./build/pack/bin/scalac -J-Xss4M -J-Xmx4G test/files/pos/inductive-implicits.scala

// HList   scalac   scalac +
// Size             inductive heuristics
//  50        6       4
// 100       15       5
// 150       36       6
// 200       68       6
// 250      114       7
// 300      179       9

milessabin

scala> def stuff(xs: ::[Int]): Int = xs.head
stuff: (xs: ::[Int])Int

scala> stuff(Nil)
<console>:13: error: type mismatch;
 found   : scala.collection.immutable.Nil.type
 required: ::[Int]
       stuff(Nil)
             ^

milessabin

scala> def narrow[T <: Singleton](t: T): T {} = t
narrow: [T <: Singleton](t: T)T

scala> narrow(23)
res1: 23 = 23

scala> var x = narrow(42)
x: 42 = 42

scala>

milessabin

### Keybase proof

I hereby claim:

  * I am milessabin on github.
  * I am milessabin (https://keybase.io/milessabin) on keybase.
  * I have a public key whose fingerprint is 87D4 DCA4 07A5 556C 0BAD  D01F 420D 4BEE 9FA4 7A44

To claim this, I am signing this object:

milessabin

object Test {
  def one[T <: 1](t: T): T = t
  final val o = one(1)
  o: 1

  def narrow[T <: Singleton](t: T): T {} = t
  final val fn0 = narrow(23)
  fn0: 23

  val n0 = narrow(23)