From b4ab528e1995ab7017b55a899d970feee0c74edb Mon Sep 17 00:00:00 2001
From: Peter Mikkelsen <petermikkelsen10@gmail.com>
Date: Sat, 29 Jan 2022 00:06:51 +0000
Subject: =?UTF-8?q?Implement=20intersection=20=E2=88=A9?=
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---
 apl9.h      |  1 +
 functions.c | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/apl9.h b/apl9.h
index d7cb4e1..a8d234f 100644
--- a/apl9.h
+++ b/apl9.h
@@ -346,6 +346,7 @@ Array *fnIndex(Array *, Array *);
 Array *fnIndexOf(Array *, Array *);
 Array *fnMembership(Array *, Array *);
 Array *fnUnion(Array *, Array *);
+Array *fnIntersection(Array *, Array *);
 Array *fnExcluding(Array *, Array *);
 Array *fnCatenateLast(Array *, Array *);
 Array *fnCatenateFirst(Array *, Array *);
diff --git a/functions.c b/functions.c
index 6e0c6b6..ed0fb36 100644
--- a/functions.c
+++ b/functions.c
@@ -105,7 +105,7 @@ fndyad dyadfunctiondefs[] = {
 	fnMembership, /* ∊ */
 	0, /* ⍷ */
 	fnUnion, /* ∪ */
-	0, /* ∩ */
+	fnIntersection, /* ∩ */
 	fnExcluding, /* ~ */
 	fnCatenateLast, /* , */
 	fnCatenateFirst, /* ⍪ */
@@ -1237,6 +1237,14 @@ fnUnion(Array *left, Array *right)
 	return rundfn(L"⍺⍪⍵~⍺", nil, nil, left, right);
 }
 
+Array *
+fnIntersection(Array *left, Array *right)
+{
+	if(left->rank > 1 || right->rank > 1)
+		throwerror(nil, ERank);
+	return rundfn(L"(⍺∊⍵)⌿⍺", nil, nil, left, right);
+}
+
 Array *
 fnExcluding(Array *left, Array *right)
 {
-- 
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