What to Import

Most Places

import effectie.core._
import effectie.syntax.all._

import effectie.core._ // for Fx
import effectie.syntax.all._ // for effectOf(), pureOf(), errorOf(), etc.

def foo[F[_]: Fx](n: Int): F[int] =
  for {
    n2 <- bar(n)
  } yield n + n2

For Main Method

You need instances for Fx when you actually run your program. It's usually only one place where you put the main method.

Fx[F] Instance

For the instance of Fx[F],

import effectie.instances.ce2.fx._

Example

import cats._
import cats.syntax.all._

import effectie.core._
import effectie.syntax.all._

trait Foo[F[_]] {
  def foo(n: Int): F[Int]
}
object Foo {
  def apply[F[_]: Fx: Monad]: Foo[F] = new FooF[F]
  
  private class FooF[F[_]: Fx: Monad] extends Foo[F] {
    def foo(n: Int): F[Int] = {
      for {
        n2 <- 
          if (n > 0)
            pureOf(n * 2)
          else
            pureOf(n * n)
        n3 <- pureOf(n2 * 3)
        n4 <- pureOf(n2 * 2)
      } yield n3 + n4
    }
  }
}

import cats.effect._

object MyApp extends IOApp.Simple {

  import effectie.instances.ce2.fx._
  
  def run: IO[Unit] = {
    for {
      n <- Foo[IO].foo(123)
      _ <- putStrLn(s"Result: ${n.toString}")
    } yield ()
  }

}