TryT

As a monad transformer, TryT should be used with another monadic data type, like scala.Function0.

import cats.instances.function._
import scala.util._
import com.thoughtworks.zerocost.tryt._
type TryName[+A] = TryT[Function0, A]

Given a validate function,

def validate(s: String): Int = s.toInt

when creating a TryT-transformed scala.Function0 from the validate,

import cats.syntax.all._
val invalidTry: TryName[Int] = TryT(() => Try(validate("invalid input")))

then the exceptions thrown in validate call should be converted to a scala.util.Failure;

val TryT(failure) = invalidTry
failure() should be(an[Failure[_]])

and when there is no exception thrown in validate call,

val validTry: TryName[Int] = validate("42").pure[TryName]

then the result of validate call should be converted to a scala.util.Success;

val TryT(success) = validTry
success() should be(Success(42))

and when the TryT-transformed scala.Function0 is built from a for-comprehension,

val invalidForComprehension: TryName[Int] = validate("42").pure[TryName].flatMap { i =>
  validate("invalid input").pure[TryName].map { j =>
    i + j
  }
}

then the exceptions thrown in the for-comprehension should be converted to a scala.util.Failure;

val TryT(failure2) = invalidTry
failure2() should be(an[Failure[_]])