ReaderLocal.kt

data class ContextA(val valueA: String, val valueB: Int)
data class ContextB(val valueB: Int, val valueC: Int, val valueD: Double)

val theReader: Reader<Int, String> =
  Reader().lift { b: Int -> "The number is $b!!!" }



val theReaderInA: Reader<ContextA, String> = theReader
  .local(ContextA::valueB::get)

val theReaderInB: Reader<ContextB, String> = theReader
  .local(ContextB::valueB::get)



theReaderInA
  .runId(ContextA(valueA = "I'm string", valueB = 1))

// => The number is 1!!!



theReaderInB
  .runId(ContextB(valueB = 3, valueC = 1, valueD = 1.3))

// => The number is 3!!!