Bfect

A collection of bifunctor effect typeclasses, with instances for ZIO and conversions for cats-effect.

Project structure

• bfect-core - A collection of bifunctor effect typeclasses, based loosely around the structure of cats-effect
• bfect-testing - An implementation of a bifunctor state monad along with instances for the bfect-core typeclasses
• bfect-interop-cats - Implicit conversions between the bfect-core typeclasses and their analogs in cats-core and cats-effect
• bfect-interop-fs2 - Utilities for interoperation with fs2
• bfect-interop-zio - Instances of the bfect-core typeclasses for the ZIO IO monad
• bfect-io - A half-finished bifunctor IO monad (don't use this)

Each of these are available through Maven Central, just add them to your project with your favourite build tool.

Typeclasses

Typeclass | Cats equivalent | Comment | ----------|-----------------|---------| Bifunctor (BFunctor) | cats.Functor/cats.Bifunctor | Functor with biMap and its derivations (map/rightMap, leftMap) | BifunctorMonad (BMonad) | cats.Monad | Monad. Adds flatMap, rightPure and leftPure. | BifunctorMonadError (BME) | cats.MonadError | Represents the ability to handle errors with handleErrorWith. Comes with the alias BME. | effects.Bracket | cats.effect.Bracket | Bracket. Represents the pure equivalent of try/finally | effects.Now | cats.effect.Timer | Represents the ability to create a timestamp | effects.Timer | cats.effect.Timer | Extends Now with the ability to delay execution for a period of time | effects.Die | | Extends BifunctorMonadError with the ability to suspend an effect that fails in an unchecked manner | effects.Sync | cats.effect.Sync | Extends Die with the ability to suspend arbitrary synchronous effects | effects.Async | cats.effect.Async | Extends Sync with the ability to register asynchronous effects | effects.Concurrent | cats.effect.Concurrent | Represents the effect of starting and cancelling tasks | effects.extra.Console | | Represents the effect of writing to the console | effects.extra.EnvVars | | Represents the effect of accessing environment variables | effects.extra.Resources | | Represents the effect of accessing Java resources | effects.extra.Calendar | | Extends Now with the ability to determine the system timezone, enabling computation of the local date and so on. |

Note that unlike in cats, Bracket and Concurrent are not part of the main inheritance chain that includes Sync and Async

Usage

Use the following imports:

• import au.id.tmm.bfect.syntax.all._ for extension methods
• import au.id.tmm.bfect.instances.all._ for instances
• import au.id.tmm.bfect.implicits._ for everything

import au.id.tmm.bfect.effects.Sync
import au.id.tmm.bfect.implicits._

// Companion objects provide static methods:

def hello1[F[_, _] : Sync]: F[Nothing, String] = Sync[F].pure("hello")
def hello2[F[_, _] : Sync]: F[Nothing, String] = Sync.pure("hello")

def print1[F[_, _] : Sync](string: String): F[Nothing, Unit] = Sync[F].sync(println(string))
def print2[F[_, _] : Sync](string: String): F[Nothing, Unit] = Sync.sync(println(string))

// Sync.Ops provides instance methods. The following are equivalent:

def printHello1[F[_, _] : Sync]: F[Nothing, Unit] = Sync[F].flatMap(hello1)(print1)
def printHello2[F[_, _] : Sync]: F[Nothing, Unit] = hello1.flatMap(print1)

// Importing Sync.Ops enables for-yield syntax:

def printHello3[F[_, _] : Sync]: F[Nothing, Unit] =
  for {
    hello <- hello1
    _     <- print1(hello)
  } yield ()

Cats interoperation

The bfect-interop-cats package provides implicits for interoperation with Cats. This includes instances for effect types using EitherT. The easiest way to access these is with the following import:

import au.id.tmm.bfect.interop.cats.implicits._