fix #1398

scalaz · Jun 15, 2017 · 86bce70 · 86bce70
1 parent f6f4d25
commit 86bce70
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Showing 2 changed files with 23 additions and 5 deletions.
diff --git a/core/src/main/scala/scalaz/Foldable.scala b/core/src/main/scala/scalaz/Foldable.scala
@@ -253,9 +253,20 @@ trait Foldable[F[_]]  { self =>
     } { 
       case (x @ ((amin, amax, bmin, bmax)), a) => 
         val b = f(a) 
-        if (Order[B].order(b, bmin) == LT) (a, amax, b, bmax)
-        else if (Order[B].order(b, bmax) == GT) (amin, a, bmin, b)
-        else x
+        val greaterThanOrEq = Order[B].greaterThanOrEqual(b, bmax)
+        if(Order[B].lessThanOrEqual(b, bmin)) {
+          if(greaterThanOrEq) {
+            (a, a, b, b)
+          } else {
+            (a, amax, b, bmax)
+          }
+        } else {
+          if(greaterThanOrEq) {
+            (amin, a, bmin, b)
+          } else {
+            x
+          }
+        }
     } map {
       case (amin, amax, _, _) => (amin, amax)
     }

diff --git a/tests/src/test/scala/scalaz/FoldableTest.scala b/tests/src/test/scala/scalaz/FoldableTest.scala
@@ -69,10 +69,17 @@ object FoldableTest extends SpecLite {
       (xs extremaOf f) must_== (xs minimumOf f).tuple(xs maximumOf f)
   }
   "extremaBy" ! forAll {
-    (xs: List[Int]) => 
-      val f: Int => Double = 1D + _
+    (xs: List[Int], f: Int => Int) =>
       (xs extremaBy f) must_== (xs minimumBy f).tuple(xs maximumBy f)
   }
+  "extremaBy consistent with minimumBy/maximumBy" ! {
+    val xs = (1 to 6).toList
+    val f: Int => Int = _ % 3
+    (xs extremaBy f) must_== (xs minimumBy f).tuple(xs maximumBy f)
+
+    val g: Int => Int = _ => 0
+    (xs extremaBy g) must_== (xs minimumBy g).tuple(xs maximumBy g)
+  }
 
   "distinct" ! forAll {
     (xs: List[Int]) =>