//arrow-core/arrow.core/Either/mapLeft
mapLeft
common inline fun <C> mapLeft(f: (A) -> C): Either<C, B>
The given function is applied if this is a Left.
Example:
import arrow.core.*
fun main() {
Either.Right(12).mapLeft { "flower" } // Result: Right(12)
Either.Left(12).mapLeft { "flower" } // Result: Left("flower")
}