From b42e3f6f373c8416ffdea633386f0a96bd1036ef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=A9mie=20Gillet?= <jie.gillet@gmail.com>
Date: Sun, 24 May 2020 17:10:24 +0900
Subject: [PATCH] IFS in Haskell

---
 contents/IFS/IFS.md              |  4 ++++
 contents/IFS/code/haskell/IFS.hs | 30 ++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100644 contents/IFS/code/haskell/IFS.hs

diff --git a/contents/IFS/IFS.md b/contents/IFS/IFS.md
index 69e8f41ac..7b87b23f4 100644
--- a/contents/IFS/IFS.md
+++ b/contents/IFS/IFS.md
@@ -128,6 +128,8 @@ Here, instead of tracking children of children, we track a single individual tha
 {% method %}
 {% sample lang="jl" %}
 [import:4-17, lang:"julia"](code/julia/IFS.jl)
+{% sample lang="hs" %}
+[import:7-13, lang:"haskell"](code/haskell/IFS.hs)
 {% sample lang="cpp" %}
 [import:39-52, lang:"cpp"](code/c++/IFS.cpp)
 {% endmethod %}
@@ -193,6 +195,8 @@ In addition, we have written the chaos game code to take in a set of points so t
 {% method %}
 {% sample lang="jl" %}
 [import, lang:"julia"](code/julia/IFS.jl)
+{% sample lang="hs" %}
+[import, lang:"haskell"](code/haskell/IFS.hs)
 {% sample lang="cpp" %}
 [import, lang:"cpp"](code/c++/IFS.cpp)
 {% endmethod %}
diff --git a/contents/IFS/code/haskell/IFS.hs b/contents/IFS/code/haskell/IFS.hs
new file mode 100644
index 000000000..9e8f4ef70
--- /dev/null
+++ b/contents/IFS/code/haskell/IFS.hs
@@ -0,0 +1,30 @@
+import Data.Array ((!), Array, bounds, listArray)
+import Data.List (intercalate)
+import System.Random
+
+data Point = Point Double Double
+
+chaosGame :: RandomGen g => g -> Int -> Array Int (Point -> Point) -> [Point]
+chaosGame g n hutchinson = take n points
+  where
+    (x, g') = random g
+    (y, g'') = random g'
+    choices = randomRs (bounds hutchinson) g''
+    points = Point x y : zipWith (hutchinson !) choices points
+
+main :: IO ()
+main = do
+  g <- newStdGen
+
+  let midPoint (Point a b) (Point x y) = Point ((a + x) / 2) ((b + y) / 2)
+      sierpinski =
+        listArray
+          (1, 3)
+          [ midPoint (Point 0 0),
+            midPoint (Point 0.5 (sqrt 0.75)),
+            midPoint (Point 1 0)
+          ]
+      points = chaosGame g 10000 sierpinski
+      showPoint (Point x y) = show x ++ "\t" ++ show y
+
+  writeFile "out.dat" $ intercalate "\n" $ map showPoint points