DateManipulate.scala

import java.time.LocalDate

val today = LocalDate.now
println(s"today is $today")

/** 2つの指定日とその間の日からなるLocalDateのシーケンス（昇順）を返す */
def rangeDays(from: LocalDate, to: LocalDate): Seq[LocalDate] =
  Iterator.iterate(from)(_.plusDays(1)).takeWhile(!_.isAfter(to)).toSeq

rangeDays(today, today.plusDays(5)).foreach(println)
// =>  List(2017-09-11, 2017-09-12, 2017-09-13, 2017-09-14, 2017-09-15, 2017-09-16)

/** 指定日を含むn日間のLocalDateのシーケンス（昇順）を返す */
def listDays(from: LocalDate, days: Int): Seq[LocalDate] =
  Iterator.tabulate(days)(i => from.plusDays(i)).toSeq

listDays(today, 3).foreach(println)
// => List(2017-09-11, 2017-09-12, 2017-09-13)

/** ↑にステップを導入したもの */
def listDaysWithStep(from: LocalDate, days: Int, step: Int): Seq[LocalDate] =
  Iterator.range(0, days, step).map(from.plusDays(_)).toSeq

listDaysWithStep(today, 10, 3).foreach(println)
// => List(2017-09-11, 2017-09-14, 2017-09-17, 2017-09-20)