isLeft

inline fun isLeft(predicate: (A) -> Boolean): Boolean(source)

Returns false if Right or returns the result of the given predicate to the Left value.

import arrow.core.Either
import arrow.core.Either.Left
import arrow.core.Either.Right
import io.kotest.matchers.shouldBe

fun test() {
 Left(12).isLeft { it 10 } shouldBe true
 Left(7).isLeft { it 10 } shouldBe false

 val right: Either<Int, String> = Right("Hello World")
 right.isLeft { it 10 } shouldBe false
}