Added flatMap

tribune-core/src/main/kotlin/com/sksamuel/tribune/core/map.kt

@@ -36,6 +36,7 @@ fun <I, A, B, E> Parser<I, A?, E>.mapIfNotNull(f: (A) -> B): Parser<I, B?, E> =
  *
  * @return a parser which returns the modified and flattened result of this parser.
  */
+@JvmName("deprecatedFlatMap")
 @Deprecated(message = "Deprecated. Use transformEither()", replaceWith = ReplaceWith("transformEither(f)"))
 fun <I, A, B, E> Parser<I, A, E>.flatMap(f: (A) -> EitherNel<E, B>): Parser<I, B, E> =
    Parser { this@flatMap.parse(it).flatMap(f) }
@@ -48,6 +49,10 @@ fun <I, A, B, E> Parser<I, A, E>.flatMap(f: (A) -> EitherNel<E, B>): Parser<I, B
  *
  * @return a parser which returns the modified and flattened result of this parser.
  */
-fun <I, A, B, E:E2, E2> Parser<I, A, E>.transformEither(f: (A) -> EitherNel<E2, B>): Parser<I, B, E2> =
+fun <I, O, E : E2, O2, E2> Parser<I, O, E>.transformEither(f: (O) -> EitherNel<E2, O2>): Parser<I, O2, E2> =
    Parser { this@transformEither.parse(it).flatMap(f) }
 
+fun <I, O, E : E2, I2 : I, O2, E2> Parser<I, O, E>.flatMap(f: (O) -> Parser<I2, O2, E2>): Parser<I2, O2, E2> =
+   Parser { i ->
+      parse(i).flatMap { o -> f(o).parse(i) }
+   }