Problem with Cats FlatMap in my Tagless Final class

Question

I have the following class:

class MyBot[F[_] : FlatMap]

In this class I have a function:

private def handleCallback(): F[Boolean]

In my understanding this should work:

handleCallback().flatMap(..)

But it throws: cannot resolve symbol flatMap

What do I miss?

score 3 · Accepted Answer · answered Aug 25 '19 at 13:51

3

The solution of Mon Calamari did not fix my problem, but when checking FlatMap on the suggested Blog I spotted:

import cats.implicits._ which I missed - and fixed my problem - everything stayed the same.

answered Aug 25 '19 at 13:51

pme

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3

If you do not want to import a lot of implicits. You only need `import cats.syntax.flatMap._`. – Luis Miguel Mejía Suárez Aug 25 '19 at 14:40

score 1 · Answer 2 · answered Aug 25 '19 at 08:51

You'd need to summon an instance of FlatMap[F] and use its methods to flatMap:

class MyBot[F[_]](implicit F: FlatMap[F]) {

  def handleCallback: F[Boolean] = ...

  def flatMapCallback: F[Boolean] = F.flatMap(handleCallback) { bool => 
    ...
  }

}

More details in great blog from eed3si9n: http://eed3si9n.com/herding-cats/

Problem with Cats FlatMap in my Tagless Final class

2 Answers2