Merge pull request #1429 from jbgi/digits

Add digitsFrom{Int, Long, BigInt}: extract digits of a number,
scalaz · Jan 28, 2018 · cd7d850 · cd7d850
2 parents 5f915b8 + 18848b7
commit cd7d850
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Showing 2 changed files with 41 additions and 20 deletions.
diff --git a/core/src/main/scala/scalaz/Digit.scala b/core/src/main/scala/scalaz/Digit.scala
@@ -51,33 +51,33 @@ object Digit extends DigitInstances {
     override val toInt = 9
   }
 
-  val digits: IList[Digit] = IList(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9)
+  private val digitsArray: Array[Digit] = Array(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9)
+
+  val digits: IList[Digit] = IList(digitsArray : _*)
 
   implicit def DigitLong(d: Digit): Long = d.toLong
 
-  def digitFromChar(c: Char): Option[Digit] =
-    digits.find(_.toChar == c)
+  def digitFromChar(c: Char): Option[Digit] = digitFromInt(c.toInt - 48)
 
   def digitFromInt(i: Int): Option[Digit] =
-    digits.find(_.toInt == i)
+    if (0 <= i && i <= 9) Some(digitsArray(i)) else None
 
   def digitFromLong(i: Long): Option[Digit] =
-    digits.find(_.toLong == i)
-
-  def mod10Digit(i: Int): Digit =
-    i match {
-      case 0 => _0
-      case 1 => _1
-      case 2 => _2
-      case 3 => _3
-      case 4 => _4
-      case 5 => _5
-      case 6 => _6
-      case 7 => _7
-      case 8 => _8
-      case 9 => _9
-      case _ => mod10Digit(scala.math.abs(i) % 10)
-    }
+    if (0L <= i && i <= 9L) Some(digitsArray(i.toInt)) else None
+
+  def digitsFromInt(i: Int): NonEmptyList[Digit] = digitsFromNumberString(i.toString)
+
+  def digitsFromLong(l: Long): NonEmptyList[Digit] = digitsFromNumberString(l.toString)
+
+  def digitsFromBigInt(b: BigInt): NonEmptyList[Digit] = digitsFromNumberString(b.toString)
+
+  private def digitsFromNumberString(number: String): NonEmptyList[Digit] = {
+    val (head, tail) = number.stripPrefix("-").splitAt(1)
+    NonEmptyList.nel(
+      digitsArray(head.charAt(0).toInt - 48), tail.foldRight(IList.empty[Digit]) ((c, ds) => digitsArray(c.toInt - 48) ::  ds))
+  }
+
+  def mod10Digit(i: Int): Digit = digitsArray(scala.math.abs(i % 10))
 
   def longDigits[F[_]](digits: F[Digit])(implicit F: Foldable[F]): Long =
     F.foldLeft(digits, 0L)((n, a) => n * 10L + (a: Digit))

diff --git a/tests/src/test/scala/scalaz/DigitTest.scala b/tests/src/test/scala/scalaz/DigitTest.scala
@@ -1,9 +1,30 @@
 package scalaz
 
+import Scalaz._
 import scalaz.scalacheck.ScalazProperties._
 import scalaz.scalacheck.ScalazArbitrary._
+import org.scalacheck.Prop.forAll
 
 object DigitTest extends SpecLite {
   checkAll(enum.laws[Digit])
   checkAll(monoid.laws[Digit])
+
+  "correctly extract int digits" ! forAll {
+    (i: Int) => {
+      Digit.digitsFromInt(i).longDigits must_===(scala.math.abs(i.toLong))
+    }
+  }
+
+  "correctly extract long digits" ! forAll {
+    (i: Long) => {
+      Digit.digitsFromLong(i).map(_.toInt.toString).suml must_===(i.toString.stripPrefix("-"))
+    }
+  }
+
+  "correctly extract bigint digits" ! forAll {
+    (i: BigInt) => {
+      Digit.digitsFromBigInt(i).map(_.toInt.toString).suml must_===(i.toString.stripPrefix("-"))
+    }
+  }
+
 }