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Merge pull request #157 from abo64/exercise-lense-person
exercise lense-person
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‎config.json‎

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"parallel-letter-frequency",
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"acronym",
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"zipper",
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"forth"
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"forth",
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"lens-person"
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],
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"exercises": [
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{
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"slug": "forth",
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"difficulty": 1,
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"topics": [
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]
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},
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{
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"slug": "lens-person",
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"difficulty": 1,
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"topics": [
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]
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}
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],

‎exercises/lens-person/README.md‎

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# Lens Person
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Use lenses to manipulate (get, set, modify) immutable objects.
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Updating fields of nested (immutable) objects is kind of annoying in Scala. One solution
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is to use [lenses](https://wiki.haskell.org/Lens).
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Implement several class attribute accessing functions using lenses, you may use any library you want. One good choice could be [Monocle](https://julien-truffaut.github.io/Monocle/].
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The test suite also allows you to avoid lenses alltogether so you can experiment with
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different approaches.
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The Scala exercises assume an SBT project scheme. The exercise solution source
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should be placed within the exercise directory/src/main/scala. The exercise
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unit tests can be found within the exercise directory/src/test/scala.
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To run the tests simply run the command `sbt test` in the exercise directory.
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For more detailed info about the Scala track see the [help
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page](http://help.exercism.io/getting-started-with-scala.html).

‎exercises/lens-person/build.sbt‎

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scalaVersion := "2.11.8"
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libraryDependencies += "org.scalatest" % "scalatest_2.11" % "2.2.5" % "test"
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libraryDependencies ++= Seq(
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"com.github.julien-truffaut" % "monocle-core_2.11" % "1.2.2",
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"com.github.julien-truffaut" % "monocle-macro_2.11" % "1.2.2"
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)
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libraryDependencies += "org.scalaz" %% "scalaz-core" % "7.2.6"
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‎exercises/lens-person/example.scala‎

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import java.time.LocalDate
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import LensPerson._
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trait ToBeImplemented {
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// Implement these.
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val bornStreet: Born => String
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val setCurrentStreet: String => Person => Person
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val setBirthMonth: Int => Person => Person
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// Transform both birth and current street names.
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val renameStreets: (String => String) => Person => Person
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}
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object LensPerson extends ToBeImplemented with MonocleSolution /* with ScalazSolution */ {
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case class Person(_name: Name, _born: Born, _address: Address)
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case class Name(_foreNames: String /*Space separated*/ , _surName: String)
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// Value of java.time.LocalDate.toEpochDay
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type EpochDay = Long
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case class Born(_bornAt: Address, _bornOn: EpochDay)
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case class Address(_street: String, _houseNumber: Int,
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_place: String /*Village / city*/ , _country: String)
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// Valid values of Gregorian are those for which 'java.time.LocalDate.of'
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// returns a valid LocalDate.
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case class Gregorian(_year: Int, _month: Int, _dayOfMonth: Int)
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}
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trait MonocleSolution extends ToBeImplemented {
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import monocle.PIso
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import monocle.macros.GenLens
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// Person Lenses
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val personLens = GenLens[Person]
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val name = personLens(_._name)
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val born = personLens(_._born)
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val address = personLens(_._address)
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// Name Lenses
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val nameLens = GenLens[Name]
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val foreNames = nameLens(_._foreNames)
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val surName = nameLens(_._surName)
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// Born Lenses
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val bornLens = GenLens[Born]
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val bornAt = bornLens(_._bornAt)
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val bornOn = bornLens(_._bornOn)
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// Address Lenses
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val street = GenLens[Address](_._street)
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// Gregorian Lenses
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val gregorianLens = GenLens[Gregorian]
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val dayOfMonth = gregorianLens(_._dayOfMonth)
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val month = gregorianLens(_._month)
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val year = gregorianLens(_._year)
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val bornStreet: Born => String =
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bornAt ^|-> street get
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val setCurrentStreet: String => Person => Person =
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address ^|-> street set
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val isoEpocheDayGregorian: PIso[EpochDay, EpochDay, Gregorian, Gregorian] = {
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def epochDayToGregorian(ed: EpochDay): Gregorian = {
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val ld = LocalDate.ofEpochDay(ed)
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Gregorian(ld.getYear, ld.getMonth.getValue, ld.getDayOfMonth)
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}
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def gregorianToEpochDay(g: Gregorian): EpochDay =
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LocalDate.of(g._year, g._month, g._dayOfMonth).toEpochDay
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PIso(epochDayToGregorian _)(gregorianToEpochDay _)
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}
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val setBirthMonth: Int => Person => Person =
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born ^|-> bornOn ^<-> isoEpocheDayGregorian ^|-> month set
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val renameStreets: (String => String) => Person => Person =
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f => ((born ^|-> bornAt ^|-> street modify f) .compose (address ^|-> street modify f))
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}
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trait ScalazSolution extends ToBeImplemented {
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import scalaz.Lens
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// Person Lenses
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val name = Lens.lensu[Person, Name](
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(person, name) => person.copy(_name = name), (_._name))
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val born = Lens.lensu[Person, Born](
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(person, born) => person.copy(_born = born), (_._born))
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val address = Lens.lensu[Person, Address](
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(person, address) => person.copy(_address = address), (_._address))
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// Name Lenses
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val foreNames = Lens.lensu[Name, String](
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(name, foreNames) => name.copy(_foreNames = foreNames), (_._foreNames))
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val surName = Lens.lensu[Name, String](
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(name, surName) => name.copy(_surName = surName), (_._surName))
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// Born Lenses
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val bornAt = Lens.lensu[Born, Address](
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(born, address) => born.copy(_bornAt = address), (_._bornAt))
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val bornOn = Lens.lensu[Born, EpochDay](
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(born, epochDay) => born.copy(_bornOn = epochDay), (_._bornOn))
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// Address Lenses
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val street = Lens.lensu[Address, String](
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(address, street) => address.copy(_street = street), (_._street))
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// Gregorian Lenses
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val dayOfMonth = Lens.lensu[Gregorian, Int](
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(gregorian, dayOfMonth) => gregorian.copy(_dayOfMonth = dayOfMonth), (_._dayOfMonth))
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val month = Lens.lensu[Gregorian, Int](
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(gregorian, month) => gregorian.copy(_month = month), (_._month))
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val year = Lens.lensu[Gregorian, Int](
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(gregorian, year) => gregorian.copy(_year = year), (_._year))
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val bornStreet: Born => String =
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bornAt >=> street get
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val setCurrentStreet: String => Person => Person =
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s => address >=> street set(_, s)
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def epochDayToGregorian(ed: EpochDay): Gregorian = {
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val ld = LocalDate.ofEpochDay(ed)
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Gregorian(ld.getYear, ld.getMonth.getValue, ld.getDayOfMonth)
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}
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def gregorianToEpochDay(g: Gregorian): EpochDay =
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LocalDate.of(g._year, g._month, g._dayOfMonth).toEpochDay
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val setBirthMonth: Int => Person => Person =
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m => born >=> bornOn =>= setMonth(m)
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val setMonth: Int => EpochDay => EpochDay =
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newMonth => oldEpochDay => {
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val Gregorian(year, _, day) = epochDayToGregorian(oldEpochDay)
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val newGregorian = Gregorian(year, newMonth, day)
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gregorianToEpochDay(newGregorian)
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}
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val renameStreets: (String => String) => Person => Person =
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f => ((born >=> bornAt >=> street =>= f) .compose (address >=> street =>= f))
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}

‎exercises/lens-person/src/main/scala/LensPerson.scala‎

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import java.time.LocalDate
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object LensPerson {
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case class Person(_name: Name, _born: Born, _address: Address)
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case class Name(_foreNames: String /*Space separated*/ , _surName: String)
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// Value of java.time.LocalDate.toEpochDay
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type EpochDay = Long
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case class Born(_bornAt: Address, _bornOn: EpochDay)
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case class Address(_street: String, _houseNumber: Int,
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_place: String /*Village / city*/ , _country: String)
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// Valid values of Gregorian are those for which 'java.time.LocalDate.of'
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// returns a valid LocalDate.
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case class Gregorian(_year: Int, _month: Int, _dayOfMonth: Int)
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// Implement these.
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val bornStreet: Born => String = ???
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val setCurrentStreet: String => Person => Person = ???
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val setBirthMonth: Int => Person => Person = ???
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// Transform both birth and current street names.
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val renameStreets: (String => String) => Person => Person = ???
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}

‎exercises/lens-person/src/test/scala/LensPersonTest.scala‎

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import org.scalatest.{FunSuite, Matchers}
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import java.time.LocalDate
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import LensPerson._
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class LensPersonTest extends FunSuite with Matchers {
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val testPerson =
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Person(
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_name = Name(
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_foreNames = "Jane Joanna",
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_surName = "Doe"),
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_born = Born(
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_bornAt = Address(
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_street = "Longway",
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_houseNumber = 1024,
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_place = "Springfield",
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_country = "United States"),
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_bornOn = toEpochDay(1984, 4, 12)),
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_address = Address(
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_street = "Shortlane",
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_houseNumber = 2,
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_place = "Fallmeadow",
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_country = "Canada"))
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def toEpochDay(year: Int, month: Int, dayOfMonth: Int) =
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LocalDate.of(year, month, dayOfMonth).toEpochDay
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test("bornStreet") {
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bornStreet(testPerson._born) should be ("Longway")
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}
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test("setCurrentStreet") {
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pending
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(setCurrentStreet("Middleroad")(testPerson))._address._street should be ("Middleroad")
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}
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test("setBirthMonth") {
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pending
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setBirthMonth(9)(testPerson)._born._bornOn should be (toEpochDay(1984, 9, 12))
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}
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test("renameStreets birth") {
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pending
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renameStreets(_.toUpperCase)(testPerson)._born._bornAt._street should be ("LONGWAY")
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}
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test("renameStreets current") {
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pending
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renameStreets(_.toUpperCase)(testPerson)._address._street should be ("SHORTLANE")
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}
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}

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