From 3a341d479d18bb593646516dc7831feead8d8548 Mon Sep 17 00:00:00 2001
From: David Chambers <dc@davidchambers.me>
Date: Wed, 3 Jan 2018 23:06:59 +0100
Subject: [PATCH] =?UTF-8?q?add=20derivation=20from=20=E2=80=98concat?=
 =?UTF-8?q?=E2=80=99,=20=E2=80=98of=E2=80=99,=20=E2=80=98zero=E2=80=99,=20?=
 =?UTF-8?q?and=20=E2=80=98reduce=E2=80=99?=
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---
 README.md | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/README.md b/README.md
index be37999..4778fad 100644
--- a/README.md
+++ b/README.md
@@ -886,6 +886,16 @@ to implement certain methods then derive the remaining methods. Derivations:
     }
     ```
 
+  - [`filter`][] may be derived from [`concat`][], [`of`][], [`zero`][], and
+    [`reduce`][]:
+
+    ```js
+    function(pred) {
+      var F = this.constructor;
+      return this.reduce((f, x) => pred(x) ? f.concat(F.of(x)) : f, F.zero());
+    }
+    ```
+
 If a data type provides a method which *could* be derived, its behaviour must
 be equivalent to that of the derivation (or derivations).