OptionT

Extension Methods for OptionT

import extras.cats.syntax.option._

or

import extras.cats.syntax.all._

optionT / t for F[Option[A]]

When you have foa: F[Option[A]], instead of OptionT(foa), you can simply do

foa.optionT // OptionT[F, A]
// or
foa.t // OptionT[F, A]

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

import extras.cats.syntax.all._

val foa = IO.pure(1.some)
// foa: IO[Option[Int]] = Pure(a = Some(value = 1))
foa.t
// res1: cats.data.OptionT[IO, Int] = OptionT(
//   value = Pure(a = Some(value = 1))
// )

val f = IO(println("Hello").some)
// f: IO[Option[Unit]] = Delay(
//   thunk = <function0>,
//   trace = StackTrace(
// ...
f.t
// res2: cats.data.OptionT[IO, Unit] = OptionT(
//   value = Delay(
//     thunk = <function0>,
// ...

optionT / t for Option[A]

When you have oa: Option[A], instead of OptionT.fromOption[F](oa), you can simply do

oa.optionT[F] // OptionT[F, A]
// or
oa.t[F] // OptionT[F, A]

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

import extras.cats.syntax.all._

val oa = 1.some
// oa: Option[Int] = Some(value = 1)
oa.t[IO]
// res4: cats.data.OptionT[IO, Int] = OptionT(
//   value = Pure(a = Some(value = 1))
// )

someT for F[A]

When you have fa: F[A], instead of OptionT.liftF(fa), you can simply do

fa.someT // OptionT[F, A]

import cats.effect._

import extras.cats.syntax.all._

val fa = IO.pure(1)
// fa: IO[Int] = Pure(a = 1)
fa.someT
// res6: cats.data.OptionT[IO, Int] = OptionT(
//   value = Map(
//     source = Pure(a = 1),
// ...

val f = IO(println("Hello"))
// f: IO[Unit] = Delay(
//   thunk = <function0>,
//   trace = StackTrace(
// ...
f.someT
// res7: cats.data.OptionT[IO, Unit] = OptionT(
//   value = Map(
//     source = Delay(
// ...

someTF for A

When you have a: A, instead of OptionT.some(a), you can simply do

a.someTF[F] // OptionT[F, A]

import cats.effect._

import extras.cats.syntax.all._

val a = 1
// a: Int = 1
a.someTF[IO]
// res9: cats.data.OptionT[IO, Int] = OptionT(
//   value = Pure(a = Some(value = 1))
// )

Example

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

import extras.cats.syntax.all._

final case class MyError(message: String)

def foo[F[_]: Sync](n: Int): F[Int] = Sync[F].pure(n * 2)

def bar[F[_]: Sync](n: Int): F[Option[Int]] =
  if (n < 0)
    Sync[F].pure(none[Int])
  else
    Sync[F].pure((n + 100).some)

def divide[F[_]: Sync](a: Int, b: Int): F[Option[Int]] =
  if (b == 0)
    none[Int].pure[F]
  else
    Sync[F].delay((a / b).some)

def run[F[_]: Sync](): F[Option[Int]] = (for {
  a <- foo(123).someT
  b <- 2.someTF[F]
  c <- bar(b).optionT
  d <- divide(a, c).t
} yield d).value

println(run[IO]().unsafeRunSync())
// Some(2)