shapeless

I would like to write def parse[T <: HList](list: List[String]): Validation[T] . list could be List("fooid", "barid") , and T FooId :: BarId :: HNil , and a typeclass Parse[T] which implements String => Validation[FooId] . How would I write said parse , which parses the list into T ? I'm not sure how to summon the implicit typeclasses for each of the elements of T . We can adapt the code from shapeless.ops.traversable.FromTraversable . I'm not sure what your Validation type is, but I used it as an alias for scalaz.ValidationNel[String, A] below (mostly so I could use the string syntax to

I'm using libraryDependencies += "com.chuusai" %% "shapeless" % "2.2.4" Currently i have model HList types like sealed trait Section case class Header(...) extends Section case class Customer(...) extends Section case class Supplier(...) extends Section case class Tech(...) extends Section type ContractView = Header :: (Customer :: Supplier :: HNil) :: Tech :: HNil In my user code, i'd like to filter technical sections that are not supposed to view using foldRight as proposed in this answer : trait collectAllRF extends Poly2 { implicit def atAny[L <: HList, X] = at[X, L](_ :: _) } object

Suppose I was dealing with a simple colon-delimited text protocol that looked something like: Event:005003:information:2013 12 06 12 37 55:n3.swmml20861:1:Full client swmml20861 registered [entry=280 PID=20864 queue=0x4ca9001b] RSET:m3node:AUTRS:1-1-24:A:0:LOADSHARE:INHIBITED:0 M3UA_IP_LINK:m3node:AUT001LKSET1:AUT001LK1:r OPC:m3node:1-10-2(P):A7:NAT0 .... I'd like to deserialize each line as an instance of a case class, but in a type-safe way. My first attempt uses type classes to define 'read' methods for each possible type that I can encounter, in addition to the 'tupled' method on the case

I want to take this pattern: def accept[T](a: RList[T]) = true def accept[T, V](a: RList[T], b: RList[V])(implicit ev: a.S =:= b.S) = true def accept[T, V, Q](a: RList[T], b: RList[V], c: RList[Q])(implicit ev: a.S =:= b.S, ev2: b.S =:= c.S) = true but have it accept a KList , instead of manually overriding for all arities. Basically I want to say, "Take any number of RList s, that have the same S member type" RList is a trait, that contains a type S . (For more background on an RList and why I'm doing this, see: Constrain function based on origin (Path Dependent type? Type Generation?) ) It

I am using a RightFolder that returns a Tuple2 and would like to return the _1 part. The first version rightFoldUntupled1 works fine but uses an additional IsComposite typeclass. In the second version rightFoldUntupled2 I try to achieve the same without IsComposite by destructuring P as a Product2[_, Values] . That doesn't work any more - the compiler is happy to witness that P is a Product2[_,_] , but as soon as I use a named type parameter for _1 it doesn't compile any more. Any idea why? The full source (with sbt ready to ~run with implicit debug output) is here: https://github.com

I am learning shapeless, and currently I am trying to create a function that does the following: given a type of an HList it returns the HList of None s, with the Option types corresponding to given HList type. For instance: create[String :: Int :: HNil] // returns None[String] :: None[Int] :: HNil So the logic is the following: def create[A <: HList] { type HT = ??? //somehow getting Head type type TT = ??? //somehow getting Tail type // if HT is HNil HNil else Option.empty[HT] :: create[TT] } Looks like the HT and TT can be provided by IsHCons def createHList[L <: HList](implicit ihc: