Matrix22Monoid.kt

interface Matrix22Monoid : Monoid<Matrix22> {
    override fun empty(): Matrix22 = Matrix22.identity
    override fun Matrix22.combine(b: Matrix22): Matrix22 {
        val (l00, l01, l10, l11) = this
        val (r00, r01, r10, r11) = b
        return Matrix22(
            l00 * r00 + l01 * r10,
            l00 * r01 + l01 * r11,
            l10 * r00 + l11 * r10,
            l10 * r01 + l11 * r11
        )
    }
}

fun Matrix22.Companion.monoid(): Monoid<Matrix22> = object : Matrix22Monoid {}