我正在尝试对HList类型进行一些计算(以执行张量代数)。到目前为止,我无法使用2.13.0-M4。
这是挑战:
type XInt = Int with Singleton
def mult[N <: XInt, M <: XInt, P <: XInt, T <: HList]
(a: N :: M :: T, b: M :: P :: T): N :: P :: T= ???
val a = 8.narrow :: 4.narrow :: HNil
val b = 4.narrow :: 5.narrow :: HNil
mult(a, b) // should yield 8 :: 5 :: HNil
答案 0 :(得分:1)
尝试
def mult[N <: XInt, M <: XInt, P <: XInt, T <: HList](a: N :: M :: T, b: M :: P :: T): N :: P :: T =
(a, b) match { case (n :: _ :: t, _ :: p :: _) => n :: p :: t }
或
def mult[N <: XInt, M <: XInt, P <: XInt, T <: HList](a: N :: M :: T, b: M :: P :: T): N :: P :: T =
a.head :: b.tail.head :: b.tail.tail
或者简单地
def mult[N <: XInt, M <: XInt, P <: XInt, T <: HList](a: N :: M :: T, b: M :: P :: T): N :: P :: T =
a.head :: b.tail