From 0b4d1ce8cabe1cdf7b46542fa18f26294303f941 Mon Sep 17 00:00:00 2001
From: Phil Freeman <paf31@cantab.net>
Date: Wed, 27 Aug 2014 11:17:25 -0700
Subject: [PATCH] Fix #1, example

---
 .gitignore               |  2 +-
 Gruntfile.js             | 13 ++++++++++++-
 bower.json               |  3 ---
 examples/Collatz.purs    | 16 ++++++++++++++++
 src/Data/Unfoldable.purs | 36 +++++++++++++++++++++---------------
 5 files changed, 50 insertions(+), 20 deletions(-)
 create mode 100644 examples/Collatz.purs

diff --git a/.gitignore b/.gitignore
index 9b41405..1bace05 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,4 +4,4 @@
 /output/
 /node_modules/
 /bower_components/
-/tmp/
+/dist/
diff --git a/Gruntfile.js b/Gruntfile.js
index e13c0ad..65dd0ae 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -17,12 +17,23 @@ module.exports = function(grunt) {
       }
     },
 
+    psc: {
+      options: {
+        modules: ["Main"],
+        main: "Main"
+      },
+      example: {
+        src: ["<%=libFiles%>", "examples/*.purs"],
+        dest: "dist/Main.js"  
+      }
+    },
+
     dotPsci: ["<%=libFiles%>"]
   });
 
   grunt.loadNpmTasks("grunt-contrib-clean");
   grunt.loadNpmTasks("grunt-purescript");
  
-  grunt.registerTask("make", ["pscMake:lib", "dotPsci"]);
+  grunt.registerTask("make", ["pscMake:lib", "dotPsci", "psc:example"]);
   grunt.registerTask("default", ["clean", "make"]);
 };
diff --git a/bower.json b/bower.json
index 6893fc8..8197887 100644
--- a/bower.json
+++ b/bower.json
@@ -18,8 +18,5 @@
     "purescript-arrays"               : "*",
     "purescript-tuples"               : "*",
     "purescript-maybe"                : "*"
-  },
-  "devDependencies": {
-    "purescript-quickcheck"           : "*"
   }
 }
diff --git a/examples/Collatz.purs b/examples/Collatz.purs
new file mode 100644
index 0000000..ee7bb3a
--- /dev/null
+++ b/examples/Collatz.purs
@@ -0,0 +1,16 @@
+module Main where
+
+import Data.Tuple
+import Data.Maybe
+import Data.Array
+import Data.Unfoldable
+
+import Debug.Trace
+
+collatz :: Number -> [Number]
+collatz = unfoldr step 
+  where
+  step 1 = Nothing
+  step n = Just $ Tuple n $ if n % 2 == 0 then n / 2 else n * 3 + 1
+
+main = print $ collatz 1000
diff --git a/src/Data/Unfoldable.purs b/src/Data/Unfoldable.purs
index 619e40e..72e790e 100644
--- a/src/Data/Unfoldable.purs
+++ b/src/Data/Unfoldable.purs
@@ -2,24 +2,30 @@ module Data.Unfoldable where
 
 import Data.Maybe
 import Data.Tuple
-import Data.Function
+import Control.Monad.Eff
+import Control.Monad.ST
 
 class Unfoldable t where
   unfoldr :: forall a b. (b -> Maybe (Tuple a b)) -> b -> t a
  
-foreign import unfoldrArray 
-  "function unfoldrArray(f, b) {\
-  \  var result = [];\
-  \  while (true) {\
-  \    var maybe = f(b);\
-  \    if (maybe.ctor === \"Data.Maybe.Nothing\") {\
-  \      return result;\
-  \    } else if (maybe.ctor === \"Data.Maybe.Just\") {\
-  \      result.push(maybe.values[0].values[0]);\
-  \      b = maybe.values[0].values[1];\
-  \    }\
-  \  }\
-  \}" :: forall a b. Fn2 (b -> Maybe (Tuple a b)) b [a]
+foreign import newEmptySTArray 
+  "function newEmptySTArray() {\
+  \  return [];\
+  \}" :: forall eff h a. Eff (st :: ST h | eff) (STArray h a)
 
 instance unfoldableArray :: Unfoldable [] where
-  unfoldr = runFn2 unfoldrArray
+  unfoldr f b = runPure (runSTArray (do
+    arr  <- newEmptySTArray
+    seed <- newSTRef b
+    idx  <- newSTRef 0
+    untilE $ do
+      b1 <- readSTRef seed
+      case f b1 of
+        Nothing -> return true
+        Just (Tuple a b2) -> do
+          i <- readSTRef idx
+          pokeSTArray arr i a
+          writeSTRef seed b2
+          writeSTRef idx (i + 1)
+          return false
+    return arr))