MeetSemilattice for longest string prefix

longerst_prefix.test.scala

//> using scala 3.5.1
//> using options -Wunused:all -deprecation -Xkind-projector -rewrite -source future-migration
//> using dep org.typelevel::algebra:2.12.0
//> using test.dep org.typelevel::discipline-munit:2.0.0
//> using test.dep org.typelevel::algebra-laws:2.12.0

import algebra.laws.LatticeLaws
import algebra.lattice.MeetSemilattice

given MeetSemilattice[String] with
  /** @todo use for DirectedSet */
  def zero: String                                    = ""

  extension (s1: String) def longestPrefixWith(s2: String) = 
    val shortest     = if s1.size < s2.size then s1 else s2
    val maxPrefixLen = shortest.indices.find(i => s1(i) != s2(i))
    maxPrefixLen.map(shortest.take).getOrElse(shortest)

  final override def meet(lhs: String, rhs: String): String = lhs.longestPrefixWith(rhs)
end given

/** Algebraically this is bounded join semilattice (or distributive lattice)
  * @see
  *   https://en.wikipedia.org/wiki/Semilattice
  * @see
  *   https://typelevel.org/cats/algebra.html
  * @todo
  *   TODO: consider interpreting it as a DirectedSet
  */
class LongestPrefixLaws extends munit.DisciplineSuite:
  checkAll("Longest prefix", LatticeLaws[String].meetSemilattice)