From 592764ded4ad2982e501640b65c539c542410a44 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Tue, 23 Dec 2014 20:08:23 -0800
Subject: [PATCH] =?UTF-8?q?math.extras:=20adding=20the=20M=C3=B6bius=20fun?=
 =?UTF-8?q?ction.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 extra/math/extras/extras-tests.factor |  9 +++++++++
 extra/math/extras/extras.factor       | 14 ++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/extra/math/extras/extras-tests.factor b/extra/math/extras/extras-tests.factor
index c5c26cb99f..3f56fe2c2e 100644
--- a/extra/math/extras/extras-tests.factor
+++ b/extra/math/extras/extras-tests.factor
@@ -148,3 +148,12 @@ IN: math.extras.test
 
 { 36100 } [ 20 iota sum-cubes ] unit-test
 { 36100 } [ 20 iota >array sum-cubes ] unit-test
+
+{
+    {
+        1 -1 -1 0 -1 1 -1 0 0 1 -1 0 -1 1 1
+        0 -1 0 -1 0 1 1 -1 0 0 1 0 0 -1 -1
+    }
+} [
+    30 [1,b] [ mobius ] map
+] unit-test
diff --git a/extra/math/extras/extras.factor b/extra/math/extras/extras.factor
index 9b2a86a285..90d8d4f19f 100644
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@@ -4,10 +4,10 @@
 USING: accessors arrays assocs assocs.extras byte-arrays
 combinators combinators.short-circuit compression.zlib fry
 grouping kernel locals math math.combinatorics math.constants
-math.functions math.order math.primes math.ranges
-math.ranges.private math.statistics math.vectors memoize parser
-random sequences sequences.extras sequences.private sets sorting
-sorting.extras ;
+math.functions math.order math.primes math.primes.factors
+math.ranges math.ranges.private math.statistics math.vectors
+memoize parser random sequences sequences.extras
+sequences.private sets sorting sorting.extras ;
 
 IN: math.extras
 
@@ -316,3 +316,9 @@ M: iota-tuple sum-squares
 GENERIC: sum-cubes ( seq -- n )
 M: object sum-cubes [ 3 ^ ] map-sum ;
 M: iota-tuple sum-cubes sum sq ;
+
+: mobius ( n -- x )
+    group-factors values [ 1 ] [
+        dup [ 1 > ] any?
+        [ drop 0 ] [ length even? 1 -1 ? ] if
+    ] if-empty ;