Using Monad Transformer from Option -> Either

Question

Given the following method,

scala> def f(x: Option[String]): Either[String, Int] = x match {
        case Some(x) => try { Right(x.toInt) } 
                        catch { 
                          case _:  NumberFormatException => Left(s"Not an int: $x") 
                        }
        case None    => Left("No String present.")
      }
f: (x: Option[String])Either[String,Int]

testing

scala> f(None)
res0: Either[String,Int] = Left(No String present.)

scala> f(Some("44"))
res2: Either[String,Int] = Right(44)

scala> f(Some("zipp"))
res3: Either[String,Int] = Left(Not an int: zipp)

How would a Monad transformer be used here?

Note - I don't know if it's a good example since it's so short (and the pattern match might be the cleanest way), but I'm curious anyway.

Monad transformers are kind of confusingly named—they're more like tools to help with composing monads than transformers from one monadic type to another. — Travis Brown, Apr 08 '15 at 17:58
I'd use a `map` here and Scalaz gives you nicer tools for going from `Option` to `Either`, but the basic approach looks reasonable to me. — Travis Brown, Apr 08 '15 at 17:59
`Option.toRight` in the standard lib seems pretty nice to me. — Michael Zajac, Apr 08 '15 at 18:09
@m-z Oh right, that's in the standard library, not Scalaz. :) — Travis Brown, Apr 08 '15 at 19:40
Of monad transformers? There are a [number of questions on here](http://stackoverflow.com/search?q=monad-transformers+scala). [Here's a potential starting point](http://stackoverflow.com/a/25950063/334519). — Travis Brown, Apr 08 '15 at 20:00

Using Monad Transformer from Option -> Either

0 Answers0