From e2ce8e0c7189edae2f602ee35ca2d3e971f00cf1 Mon Sep 17 00:00:00 2001
From: Tom <tomjharding@live.co.uk>
Date: Sun, 28 May 2017 11:54:35 +0100
Subject: [PATCH] Add `extend` instance for `Array`

While being defined for `List`, the `Array` primitive didn't previously
have a defined `Extend` instance. This has been added.
---
 src/Control/Extend.js   | 9 +++++++++
 src/Control/Extend.purs | 5 +++++
 2 files changed, 14 insertions(+)
 create mode 100644 src/Control/Extend.js

diff --git a/src/Control/Extend.js b/src/Control/Extend.js
new file mode 100644
index 0000000..05c8ecf
--- /dev/null
+++ b/src/Control/Extend.js
@@ -0,0 +1,9 @@
+"use strict";
+
+exports.arrayExtend = function(f) {
+  return function(xs) {
+    return xs.map(function (_, i, xs) {
+      return f(xs.slice(i));
+    });
+  };
+};
diff --git a/src/Control/Extend.purs b/src/Control/Extend.purs
index a47046f..28e1523 100644
--- a/src/Control/Extend.purs
+++ b/src/Control/Extend.purs
@@ -27,6 +27,11 @@ class Functor w <= Extend w where
 instance extendFn :: Semigroup w => Extend ((->) w) where
   extend f g w = f \w' -> g (w <> w')
 
+foreign import arrayExtend :: forall a b. (Array a -> b) -> Array a -> Array b
+
+instance extendArray :: Extend Array where
+  extend = arrayExtend
+
 infixr 1 extend as <<=
 
 -- | A version of `extend` with its arguments flipped.