CODEWITHSUNDEEP
scala
Midiparse
Midiparse

Reputation: 4781

Is there a typeclass for all sequences in Scala?

I'm messing around with algebraic structures, and I find the Numeric typeclass very handy for well, representing numeric values.

So I can write my monoid instance this way:

implicit def add[A: Numeric] = new Monoid[A] {
  def mempty = implicitly[Numeric[A]].zero
  def mappend(a0: A, a1: A) = implicitly[Numeric[A]].plus(a0, a1)
}

This looks like a dandy. But what can I do with sequences? I can't find a typeclass that does standard Scala collection sequences. I would like to write something like this:

def concat[A : SeqTC] = new Monoid[A] {
  def mempty = implicitly[SeqTC[A]].empty
  def mappend(a0: A, a1: A) = implicitly[SeqTC[A]].++(a0, a1)
}

Upvotes: 2

Views: 95

Answers (1)

Midiparse
Midiparse

Reputation: 4781

According to @TrustNoOne's comment, this is what I achieved to do. And it works great.

def concat[A, S[A] <: Seq[A]](implicit bf: CanBuildFrom[S[A], A, S[A]]) = new Monoid[S[A]] {
  def mempty = bf().result()
  def mappend(a0: S[A], a1: S[A]) = bf.apply().++=(a0).++=(a1).result()
}

Upvotes: 1

Related Questions