reader monad with kleisli and tuple/untupling

gistfile1.scala

import scalaz._
import Scalaz._

case class Foo(value: String)
case class Bar(value: String)
case class Baz(foo: Foo, bar: Bar)
type E = Map[String, String]

type K[M[_],A,B] = Kleisli[M,A,B]
      
def pair[M[_], E, A, B](f: K[M, E, A], g: K[M, E, B])(implicit t: Functor[M], ap: Apply[M]): K[M, E, (A,B)] = kleisli(e => (f(e) |@| g(e)).tupled)

val fooR = (e: E) => e.get("foo").map(Foo(_))
val barR = (e: E) => e.get("bar").map(Bar(_))      

def bazR(fooR: E => Option[Foo])(barR: E => Option[Bar]) = 
  for (fb <- pair(kleisli(fooR), kleisli(barR))) 
    yield Baz(fb._1, fb._2)
      
val env: E = Map("foo" -> "oof", "bar" -> "rab")
      
fooR(env) must beSome(Foo("oof"))
barR(env) must beSome(Bar("rab"))
bazR(fooR)(barR)(env) must beSome(Baz(Foo("oof"), Bar("rab")))
bazR(fooR)(barR)(Map("foo" -> "oof")) must beNone
bazR(fooR)(barR)(Map("bar" -> "rab")) must beNone