tnielens / intervalops

An interval typeclass that provides default implementation for common operations.

IntervalOps

An Interval[I] typeclass that, given an implementation of the methods start , end and an ordering of the base bound type, provides default implementation for common interval-like operations (contains, overlap , gap, etc). Optional bounds are supported.

Given an Ordering[B], instances are provided for

• (B, B)
• (Option[B], B)
• (B, Option[B])
• (Option[B], Option[B])

In the optional bound cases, None represents the minimum value in start position or the maximum value in end position.

Usage example

Working with time:

import com.github.tnielens.intervalops.Interval.Ops
import java.time.Instant

implicit val instanctOrdering: Ordering[Instant] = Ordering.fromLessThan(_.isBefore(_))
val Seq(t0, t1, t2, t3) = Seq.iterate(Instant.now(), 4)(_.plusSeconds(5))

assert(((t0, t3) overlap (t1, t2)) == (t1, t2))
assert(((t0, t3) diff (t1, t2)) == (Option((t0, t1)), Option((t2, t3))))

Interval works for any base boundary type B given an Ordering[B]. Instances for primitive types (Ordering[Int], Ordering[Double], etc) are provided by the std library.

import com.github.tnielens.intervalops.Interval.Ops

assert(((0, 10) overlap (5, 15)) == (5, 10))
assert(((0, 10) diff (6, 7)) == (Option((0, 6), Option((7, 10))))

Working with optional bounds:

import com.github.tnielens.intervalops.Interval.Ops

assert(((0, Option(10)) overlap (8, None)) == (8, Option(10)))
assert(((0, None: Option[Int]) diff (6, Some(7))) == (Option((0, Some(6)), Option((7, None)))))

Mind that Ordering[T] is not contravariant, so you have to upcast Some and None first operand values to Option for Interval.Ops to work properly.

How to create an instance of Interval[I] for a custom type

import com.github.tnielens.intervalops.Interval
import com.github.tnielens.intervalops.Interval.Ops

case class CustomInterval[B](start: B, end: B)

// if possible, put the instance definition in the companion object
// of the `CustomInterval` to avoid the import tax
implicit def customIntervalInst[B](implicit ob: Ordering[B]) =
  Interval.instance[CustomInterval[B], B, Bound[B], Bound[B]](
    c => Bound(c.start),
    c => Bound(c.end),
    (b1, b2) => CustomInterval(b1.v, b2.v)
  )

assert(CustomInterval(1, 6) contains 5)

For cases involving optional bounds, see tuples instances in the companion object Interval.