From abcd170b34191ee4c2ca4196a10f520bc62b0748 Mon Sep 17 00:00:00 2001
From: Colin Jones <trptcolin@gmail.com>
Date: Tue, 2 Nov 2010 22:55:34 -0500
Subject: [PATCH] Add recursion / factorial koan.

---
 src/koans/recursion.clj       | 21 +++++++++++++++++++++
 src/path_to_answer_sheet.clj  |  4 ++++
 src/path_to_enlightenment.clj |  3 ++-
 3 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 src/koans/recursion.clj

diff --git a/src/koans/recursion.clj b/src/koans/recursion.clj
new file mode 100644
index 0000000..7f3b2ef
--- /dev/null
+++ b/src/koans/recursion.clj
@@ -0,0 +1,21 @@
+(defn factorial [n]
+  __)
+
+(meditations
+  "Simple things may appear simple."
+  (= 1 (factorial 1))
+
+  "They may require other simple steps."
+  (= 2 (factorial 2))
+
+  "Sometimes a slightly bigger step is necessary"
+  (= 6 (factorial 3))
+
+  "And eventually you must think harder"
+  (= 24 (factorial 4))
+
+  "You can even deal with very large numbers"
+  (= (factorial 1000N) (factorial 1000N))
+
+  "But what happens when the machine limits you?"
+  (= (factorial 10000N) (factorial 10000N)))
diff --git a/src/path_to_answer_sheet.clj b/src/path_to_answer_sheet.clj
index b424263..8ea6c47 100644
--- a/src/path_to_answer_sheet.clj
+++ b/src/path_to_answer_sheet.clj
@@ -87,6 +87,10 @@
                               :a :b :c :d
                               :c :d]
                         "___" ["multiply-by-5"]}
+   "factorial" {"__" ["(loop [n n acc 1]
+                         (if (zero? n)
+                             acc
+                             (recur (dec n) (* acc n))))"]}
    })
 
 (defn replace-with [s k replacements]
diff --git a/src/path_to_enlightenment.clj b/src/path_to_enlightenment.clj
index 3d65865..4d24dfe 100644
--- a/src/path_to_enlightenment.clj
+++ b/src/path_to_enlightenment.clj
@@ -25,7 +25,8 @@
       "higher_order_functions"
       "runtime_polymorphism"
       "sequence_comprehensions"
-      "partial_functions"])
+      "partial_functions"
+      "recursion"])
 
 (defn run []
   (apply load (doall (map (partial str "koans/") ordered-koans)))