Use all available context info for healing ambiguous implicits #11274
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,4 +1,4 @@ | ||
| object Test { | ||
| def foo(x: String, y: x.type): Any = ??? | ||
| val f = foo // error | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,127 @@ | ||
| object WriterTest extends App { | ||
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| object Functor: | ||
| def apply[F[_]](using f: Functor[F]) = f | ||
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| trait Functor[F[_]]: | ||
| extension [A, B](x: F[A]) | ||
| def map(f: A => B): F[B] | ||
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| object Applicative: | ||
| def apply[F[_]](using a: Applicative[F]) = a | ||
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| trait Applicative[F[_]] extends Functor[F]: | ||
| def pure[A](x:A):F[A] | ||
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| extension [A,B](x: F[A]) | ||
| def ap(f: F[A => B]): F[B] | ||
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| def map(f: A => B): F[B] = { | ||
| x.ap(pure(f)) | ||
| } | ||
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| extension [A,B,C](fa: F[A]) def map2(fb: F[B])(f: (A,B) => C): F[C] = { | ||
| val fab: F[B => C] = fa.map((a: A) => (b: B) => f(a,b)) | ||
| fb.ap(fab) | ||
| } | ||
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| end Applicative | ||
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| object Monad: | ||
| def apply[F[_]](using m: Monad[F]) = m | ||
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| trait Monad[F[_]] extends Applicative[F]: | ||
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| // The unit value for a monad | ||
| def pure[A](x:A):F[A] | ||
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| extension[A,B](fa :F[A]) | ||
| // The fundamental composition operation | ||
| def flatMap(f :A=>F[B]):F[B] | ||
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| // Monad can also implement `ap` in terms of `map` and `flatMap` | ||
| def ap(fab: F[A => B]): F[B] = { | ||
| fab.flatMap { | ||
| f => | ||
| fa.flatMap { | ||
| a => | ||
| pure(f(a)) | ||
| } | ||
| } | ||
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| } | ||
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| end Monad | ||
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| given eitherMonad[Err]: Monad[[X] =>> Either[Err,X]] with | ||
| def pure[A](a: A): Either[Err, A] = Right(a) | ||
| extension [A,B](x: Either[Err,A]) def flatMap(f: A => Either[Err, B]) = { | ||
| x match { | ||
| case Right(a) => f(a) | ||
| case Left(err) => Left(err) | ||
| } | ||
| } | ||
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| given optionMonad: Monad[Option] with | ||
| def pure[A](a: A) = Some(a) | ||
| extension[A,B](fa: Option[A]) | ||
| def flatMap(f: A => Option[B]) = { | ||
| fa match { | ||
| case Some(a) => | ||
| f(a) | ||
| case None => | ||
| None | ||
| } | ||
| } | ||
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| given listMonad: Monad[List] with | ||
| def pure[A](a: A): List[A] = List(a) | ||
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| extension[A,B](x: List[A]) | ||
| def flatMap(f: A => List[B]): List[B] = { | ||
| x match { | ||
| case hd :: tl => f(hd) ++ tl.flatMap(f) | ||
| case Nil => Nil | ||
| } | ||
| } | ||
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| case class Transformer[F[_]: Monad,A](val wrapped: F[A]) | ||
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| given transformerMonad[F[_]: Monad]: Monad[[X] =>> Transformer[F,X]] with { | ||
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| def pure[A](a: A): Transformer[F,A] = Transformer(summon[Monad[F]].pure(a)) | ||
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| extension [A,B](fa: Transformer[F,A]) | ||
| def flatMap(f: A => Transformer[F,B]) = { | ||
| val ffa: F[B] = Monad[F].flatMap(fa.wrapped) { | ||
| case a => { | ||
| f(a).wrapped.map { | ||
| case b => | ||
| b | ||
| } | ||
| } | ||
| } | ||
| Transformer(ffa) | ||
| } | ||
| } | ||
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| type EString[A] = Either[String,A] | ||
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| def incrementEven(a: Int): Transformer[EString,Int] = { | ||
| if(a % 2 == 1) Transformer(Left("Odd number provided")) | ||
| else Transformer(Right(a + 1)) | ||
| } | ||
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| def doubleOdd(a: Int): Transformer[EString, Int] = { | ||
| if(a % 2 == 0) Transformer(Left("Even number provided")) | ||
| else Transformer(Right(a * 2)) | ||
| } | ||
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| val writerExample = incrementEven(8) | ||
| val example = | ||
| WriterTest.transformerMonad.flatMap(writerExample)(doubleOdd) | ||
| //writerExample.flatMap(doubleOdd) // Error ambiguous F | ||
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| } |
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