From 84da50b807f5cb181202bf0b157e5dcab8b8e9ed Mon Sep 17 00:00:00 2001
From: Nat Quayle Nelson <natquaylenelson@gmail.com>
Date: Thu, 10 Feb 2022 12:34:18 -0700
Subject: [PATCH] variadic intersect() function

---
 src/kiss/Kiss.hx                  |  1 +
 src/kiss/Prelude.hx               | 16 ++++++++++++++++
 src/test/cases/BasicTestCase.hx   |  4 ++++
 src/test/cases/BasicTestCase.kiss | 22 ++++++++++++++++++++++
 4 files changed, 43 insertions(+)

diff --git a/src/kiss/Kiss.hx b/src/kiss/Kiss.hx
index 078c374..7dcd7c7 100644
--- a/src/kiss/Kiss.hx
+++ b/src/kiss/Kiss.hx
@@ -116,6 +116,7 @@ class Kiss {
                 "zipKeep" => Symbol("Prelude.zipKeep"),
                 "zipDrop" => Symbol("Prelude.zipDrop"),
                 "zipThrow" => Symbol("Prelude.zipThrow"),
+                "intersect" => Symbol("Prelude.intersect"),
                 "joinPath" => Symbol("Prelude.joinPath"),
                 "readDirectory" => Symbol("Prelude.readDirectory"),
                 "substr" => Symbol("Prelude.substr"),
diff --git a/src/kiss/Prelude.hx b/src/kiss/Prelude.hx
index 587812e..b675467 100644
--- a/src/kiss/Prelude.hx
+++ b/src/kiss/Prelude.hx
@@ -246,6 +246,22 @@ class Prelude {
     public static var zipDrop:Function = Reflect.makeVarArgs(_zip.bind(_, Drop));
     public static var zipThrow:Function = Reflect.makeVarArgs(_zip.bind(_, Throw));
 
+    static function _intersect(iterables:Array<Dynamic>):kiss.List<kiss.List<Dynamic>> {
+        var iterators:Array<Iterator<Dynamic>> = [for (iterable in iterables) iterable.iterator()];
+
+        var intersections:Array<Array<Dynamic>> = [for (elem in iterators.shift()) [elem]];
+        
+        for (iterator in iterators) {
+            intersections = cast _concat([for (elem in iterator) [for (intersection in intersections) intersection.concat([elem])]]);
+        }
+        
+        return intersections;
+    }
+
+    // Return an array of every N-dimensional intersection of elements in N iterables.
+    // Callers should not rely on the order of the intersections
+    public static var intersect:Function = Reflect.makeVarArgs(_intersect);
+
     public static function enumerate(l:kiss.List<Dynamic>, startingIdx = 0):kiss.List<kiss.List<Dynamic>> {
         return zipThrow(range(startingIdx, startingIdx + l.length, 1), l);
     }
diff --git a/src/test/cases/BasicTestCase.hx b/src/test/cases/BasicTestCase.hx
index bc58d56..499220f 100644
--- a/src/test/cases/BasicTestCase.hx
+++ b/src/test/cases/BasicTestCase.hx
@@ -335,6 +335,10 @@ class BasicTestCase extends Test {
     function testContains() {
         _testContains();
     }
+
+    function testIntersect() {
+        _testIntersect();
+    }
 }
 
 class BasicObject {
diff --git a/src/test/cases/BasicTestCase.kiss b/src/test/cases/BasicTestCase.kiss
index ecb8ab6..e154f65 100644
--- a/src/test/cases/BasicTestCase.kiss
+++ b/src/test/cases/BasicTestCase.kiss
@@ -605,4 +605,26 @@
     (assert !(contains "abc" "z"))
     (assert (contains [1 2 3] 1))
     (assert !(contains [1 2 3] 5))
+    (Assert.pass))
+
+(function _testIntersect []
+    (let [intersection2d
+                (for i (the Array<Array<Dynamic>> (intersect (.split "abc" "") (.split "xyz" ""))) (i.join ""))
+            intersection3d
+                (for i (the Array<Array<Dynamic>> (intersect (.split "abc" "") (.split "xyz" "") (.split "123" ""))) (i.join ""))]
+        (assert (contains intersection2d "ax"))
+        (assert (contains intersection2d "ay"))
+        (assert (contains intersection2d "az"))
+        (assert (contains intersection2d "bx"))
+        (assert (contains intersection2d "by"))
+        (assert (contains intersection2d "bz"))
+        (assert (contains intersection2d "cx"))
+        (assert (contains intersection2d "cy"))
+        (assert (contains intersection2d "cz"))
+        (assert (contains intersection3d "ax1"))
+        (assert (contains intersection3d "ax3"))
+        (assert (contains intersection3d "bx3"))
+        (assert (contains intersection3d "cy1"))
+        (assert (contains intersection3d "cy3"))
+        )
     (Assert.pass))
\ No newline at end of file