Scala for comprehensions and withFilter

README.md

For comprehensions don't do a good job with type inference when exploding tuples. Instead they pattern match. See https://stackoverflow.com/questions/30401942/why-does-a-for-comprehension-expand-to-a-withfilter/45768795#45768795

build.sbt

libraryDependencies += "org.typelevel" %% "cats-core" % "1.0.0-MF"
scalaVersion := "2.12.2"

WillCompile.scala

import cats._
import cats.data._
import cats.implicits._

object CatsNEL extends App {
  val nss: NonEmptyList[(Int, String)] = NonEmptyList.of((1,"a"), (2, "b"), (3, "c"))
  val ss: NonEmptyList[String] = for {
    tuple <- nss
    (n, s) = tuple
  } yield s
}

WontCompile.scala

import cats._
import cats.data._
import cats.implicits._

object CatsNEL extends App {
  val nss: NonEmptyList[(Int, String)] = NonEmptyList.of((1,"a"), (2, "b"), (3, "c"))
  val ss: NonEmptyList[String] = for {
    (n, s) <- nss
  } yield s
}