List[EitherT[Future, String, CustomObj]] => EitherT[Future, String, List[CustomObj]]

How to use sequence function for List[EitherT[Future, String, CustomObj]] with custom class CustomObj ? I want something like that :

import scala.language.postfixOps

import cats.instances.list._

import cats.syntax.traverse._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Every time during compile I get

 error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A].

What does it mean <:< G[A] ?

edited Nov 21 '18 at 9:46

asked Nov 20 '18 at 14:49

Dex

@erip A note on sequencing

– Yaneeve
Nov 20 '18 at 15:22

What do you mean it "doesn't work"?

– erip
Nov 20 '18 at 15:45

I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:33

You should create a minimal example that we can copy and paste. I can't debug this without more info.

– erip
Nov 20 '18 at 17:35

1

scalacOptions += "-Ypartial-unification" . Just add it to build.sbt or pom.xml if you use maven. This does the trick. Now everything works fine. Thanks for your comments.

– Dex
Nov 21 '18 at 10:07

|
show 1 more comment

How to use sequence function for List[EitherT[Future, String, CustomObj]] with custom class CustomObj ? I want something like that :

import scala.language.postfixOps

import cats.instances.list._

import cats.syntax.traverse._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Every time during compile I get

 error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A].

What does it mean <:< G[A] ?

edited Nov 21 '18 at 9:46

asked Nov 20 '18 at 14:49

Dex

@erip A note on sequencing

– Yaneeve
Nov 20 '18 at 15:22

What do you mean it "doesn't work"?

– erip
Nov 20 '18 at 15:45

I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:33

You should create a minimal example that we can copy and paste. I can't debug this without more info.

– erip
Nov 20 '18 at 17:35

1

scalacOptions += "-Ypartial-unification" . Just add it to build.sbt or pom.xml if you use maven. This does the trick. Now everything works fine. Thanks for your comments.

– Dex
Nov 21 '18 at 10:07

|
show 1 more comment

How to use sequence function for List[EitherT[Future, String, CustomObj]] with custom class CustomObj ? I want something like that :

import scala.language.postfixOps

import cats.instances.list._

import cats.syntax.traverse._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Every time during compile I get

 error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A].

What does it mean <:< G[A] ?

edited Nov 21 '18 at 9:46

asked Nov 20 '18 at 14:49

Dex

How to use sequence function for List[EitherT[Future, String, CustomObj]] with custom class CustomObj ? I want something like that :

import scala.language.postfixOps

import cats.instances.list._

import cats.syntax.traverse._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Every time during compile I get

 error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A].

What does it mean <:< G[A] ?

scala scala-cats either

edited Nov 21 '18 at 9:46

asked Nov 20 '18 at 14:49

Dex

edited Nov 21 '18 at 9:46

asked Nov 20 '18 at 14:49

Dex

edited Nov 21 '18 at 9:46

asked Nov 20 '18 at 14:49

Dex

asked Nov 20 '18 at 14:49

Dex

asked Nov 20 '18 at 14:49

Dex

@erip A note on sequencing

– Yaneeve
Nov 20 '18 at 15:22

What do you mean it "doesn't work"?

– erip
Nov 20 '18 at 15:45

I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:33

You should create a minimal example that we can copy and paste. I can't debug this without more info.

– erip
Nov 20 '18 at 17:35

1

scalacOptions += "-Ypartial-unification" . Just add it to build.sbt or pom.xml if you use maven. This does the trick. Now everything works fine. Thanks for your comments.

– Dex
Nov 21 '18 at 10:07

|
show 1 more comment

@erip A note on sequencing

– Yaneeve
Nov 20 '18 at 15:22

What do you mean it "doesn't work"?

– erip
Nov 20 '18 at 15:45

I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:33

You should create a minimal example that we can copy and paste. I can't debug this without more info.

– erip
Nov 20 '18 at 17:35

1

scalacOptions += "-Ypartial-unification" . Just add it to build.sbt or pom.xml if you use maven. This does the trick. Now everything works fine. Thanks for your comments.

– Dex
Nov 21 '18 at 10:07

@erip A note on sequencing

– Yaneeve
Nov 20 '18 at 15:22

What do you mean it "doesn't work"?

– erip
Nov 20 '18 at 15:45

I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:33

You should create a minimal example that we can copy and paste. I can't debug this without more info.

– erip
Nov 20 '18 at 17:35

scalacOptions += "-Ypartial-unification" . Just add it to build.sbt or pom.xml if you use maven. This does the trick. Now everything works fine. Thanks for your comments.

– Dex
Nov 21 '18 at 10:07

|
show 1 more comment

1 Answer
1

active

oldest

votes

This is an edited version, code @ https://scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A:

import scala.language.postfixOps

import cats.implicits._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Initially I wrote:

Notice please that it didn't compile and produced odd compile messages
until I added import scala.concurrent.ExecutionContext.Implicits.global

And that holds true, BUT your trouble did not lie there. When I went to reproduce again, I got the error you had specified. The thing that was missing is an SBT/scalac flag: scalacOptions += "-Ypartial-unification"

edited Nov 20 '18 at 21:49

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

Thanks a lot .. but I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:31

What are SomeType1 SomeType2? They are not in your question

– Yaneeve
Nov 20 '18 at 16:42

it doesn't matter.. let it be : EitherT[Future, String, CustomObj] The error is: Cannot prove that cats.data.EitherT[Future, String, CustomObj] <:< G[A].

– Dex
Nov 20 '18 at 16:54

scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A - I have reworked it here slightly an I will amend my answer accordingly

– Yaneeve
Nov 20 '18 at 21:45

I still get error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A]. What does it mean <:< G[A]. ?

– Dex
Nov 21 '18 at 9:47

|
show 5 more comments

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1 Answer
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1 Answer
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oldest

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This is an edited version, code @ https://scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A:

import scala.language.postfixOps

import cats.implicits._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Initially I wrote:

Notice please that it didn't compile and produced odd compile messages
until I added import scala.concurrent.ExecutionContext.Implicits.global

edited Nov 20 '18 at 21:49

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

Thanks a lot .. but I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:31

What are SomeType1 SomeType2? They are not in your question

– Yaneeve
Nov 20 '18 at 16:42

it doesn't matter.. let it be : EitherT[Future, String, CustomObj] The error is: Cannot prove that cats.data.EitherT[Future, String, CustomObj] <:< G[A].

– Dex
Nov 20 '18 at 16:54

scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A - I have reworked it here slightly an I will amend my answer accordingly

– Yaneeve
Nov 20 '18 at 21:45

I still get error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A]. What does it mean <:< G[A]. ?

– Dex
Nov 21 '18 at 9:47

|
show 5 more comments

This is an edited version, code @ https://scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A:

import scala.language.postfixOps

import cats.implicits._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Initially I wrote:

Notice please that it didn't compile and produced odd compile messages
until I added import scala.concurrent.ExecutionContext.Implicits.global

edited Nov 20 '18 at 21:49

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

Thanks a lot .. but I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:31

What are SomeType1 SomeType2? They are not in your question

– Yaneeve
Nov 20 '18 at 16:42

it doesn't matter.. let it be : EitherT[Future, String, CustomObj] The error is: Cannot prove that cats.data.EitherT[Future, String, CustomObj] <:< G[A].

– Dex
Nov 20 '18 at 16:54

scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A - I have reworked it here slightly an I will amend my answer accordingly

– Yaneeve
Nov 20 '18 at 21:45

I still get error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A]. What does it mean <:< G[A]. ?

– Dex
Nov 21 '18 at 9:47

|
show 5 more comments

This is an edited version, code @ https://scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A:

import scala.language.postfixOps

import cats.implicits._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Initially I wrote:

Notice please that it didn't compile and produced odd compile messages
until I added import scala.concurrent.ExecutionContext.Implicits.global

edited Nov 20 '18 at 21:49

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

This is an edited version, code @ https://scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A:

import scala.language.postfixOps

import cats.implicits._

import cats.data.EitherT

import scala.concurrent.Future

import scala.concurrent.ExecutionContext.Implicits.global



case class CustomObj(int: Int)



private val fst: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(1))

private val snd: EitherT[Future, String, CustomObj] =

  EitherT.pure[Future, String](CustomObj(2))



val source: List[EitherT[Future, String, CustomObj]] = fst :: snd :: Nil



val result: EitherT[Future, String, List[CustomObj]] = source.sequence



import scala.concurrent.duration._

val res = scala.concurrent.Await.result(result.value, 1 second)

println(res) // Right(List(CustomObj(1), CustomObj(2)))

Initially I wrote:

Notice please that it didn't compile and produced odd compile messages
until I added import scala.concurrent.ExecutionContext.Implicits.global

edited Nov 20 '18 at 21:49

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

edited Nov 20 '18 at 21:49

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

answered Nov 20 '18 at 15:18

Yaneeve

2,75083882

Thanks a lot .. but I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:31

What are SomeType1 SomeType2? They are not in your question

– Yaneeve
Nov 20 '18 at 16:42

it doesn't matter.. let it be : EitherT[Future, String, CustomObj] The error is: Cannot prove that cats.data.EitherT[Future, String, CustomObj] <:< G[A].

– Dex
Nov 20 '18 at 16:54

scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A - I have reworked it here slightly an I will amend my answer accordingly

– Yaneeve
Nov 20 '18 at 21:45

I still get error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A]. What does it mean <:< G[A]. ?

– Dex
Nov 21 '18 at 9:47

|
show 5 more comments

Thanks a lot .. but I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:31

What are SomeType1 SomeType2? They are not in your question

– Yaneeve
Nov 20 '18 at 16:42

it doesn't matter.. let it be : EitherT[Future, String, CustomObj] The error is: Cannot prove that cats.data.EitherT[Future, String, CustomObj] <:< G[A].

– Dex
Nov 20 '18 at 16:54

scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A - I have reworked it here slightly an I will amend my answer accordingly

– Yaneeve
Nov 20 '18 at 21:45

I still get error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A]. What does it mean <:< G[A]. ?

– Dex
Nov 21 '18 at 9:47

Thanks a lot .. but I get : error: Cannot prove that cats.data.EitherT[Future, SomeType1, SomeType2] <:< G[A]. Actually I can't understand why it happens..

– Dex
Nov 20 '18 at 16:31

What are SomeType1 SomeType2? They are not in your question

– Yaneeve
Nov 20 '18 at 16:42

it doesn't matter.. let it be : EitherT[Future, String, CustomObj] The error is: Cannot prove that cats.data.EitherT[Future, String, CustomObj] <:< G[A].

– Dex
Nov 20 '18 at 16:54

scastie.scala-lang.org/Yaneeve/Jro89ZHwS3G23Aveanxc5A - I have reworked it here slightly an I will amend my answer accordingly

– Yaneeve
Nov 20 '18 at 21:45

I still get error: Cannot prove that EitherT[Future,String,CustomObj] <:< G[A]. What does it mean <:< G[A]. ?

– Dex
Nov 21 '18 at 9:47

|
show 5 more comments

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