SemiGroup

• A SemiGroup is a type class with a single operation append.
• If we throw away the right side of the SemiGroup, we get a first SemiGroup and if we through away the left side we get a second SemiGroup
• Don’t think of SemiGroup as a summation/addition (regardless of append)
• A good example ofa SemiGroup is a string, int, option…
• Law: Must be associative (but not necessarily commutative, string is not commutative, yet it is associative)

trait SemiGroup[A] {
  def append(l: => A, r: => A): A // Note: lazy parameters
}

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Resources

1. Functional Scala by John A. De Goes (Toronto Edition)
2. Scalaz SemiGroup