From ca1c340a15673dda107bc23b7d988b7490c62075 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 20:56:25 -0300
Subject: [PATCH 01/16] New excercise. collatz-conjecture

---
 exercises/collatz-conjecture/README.md        | 85 +++++++++++++++++++
 .../examples/success-standard/package.yaml    | 16 ++++
 .../success-standard/src/CollatzConjecture.hs |  9 ++
 exercises/collatz-conjecture/package.yaml     | 21 +++++
 .../src/CollatzConjectre.hs                   |  4 +
 exercises/collatz-conjecture/stack.yaml       |  1 +
 exercises/collatz-conjecture/test/Tests.hs    | 59 +++++++++++++
 7 files changed, 195 insertions(+)
 create mode 100644 exercises/collatz-conjecture/README.md
 create mode 100644 exercises/collatz-conjecture/examples/success-standard/package.yaml
 create mode 100644 exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
 create mode 100644 exercises/collatz-conjecture/package.yaml
 create mode 100644 exercises/collatz-conjecture/src/CollatzConjectre.hs
 create mode 100644 exercises/collatz-conjecture/stack.yaml
 create mode 100644 exercises/collatz-conjecture/test/Tests.hs

diff --git a/exercises/collatz-conjecture/README.md b/exercises/collatz-conjecture/README.md
new file mode 100644
index 000000000..8ad146254
--- /dev/null
+++ b/exercises/collatz-conjecture/README.md
@@ -0,0 +1,85 @@
+## Collatz Conjecture.
+
+The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+Take any positive integer n. If n is even, divide n by 2 to get n / 2. If n is
+odd, multiply n by 3 and add 1 to get 3n + 1. Repeat the process indefinitely.
+The conjecture states that no matter which number you start with, you will
+always reach 1 eventually.
+
+Given a number n, return the number of steps required to reach 1.
+
+## Examples
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps. So for input n = 12, the return value would be 9.
+
+## Getting Started
+
+For installation and learning resources, refer to the
+[exercism help page](http://exercism.io/languages/haskell).
+
+## Running the tests
+
+To run the test suite, execute the following command:
+
+```bash
+stack test
+```
+
+#### If you get an error message like this...
+
+```
+No .cabal file found in directory
+```
+
+You are probably running an old stack version and need
+to upgrade it.
+
+#### Otherwise, if you get an error message like this...
+
+```
+No compiler found, expected minor version match with...
+Try running "stack setup" to install the correct GHC...
+```
+
+Just do as it says and it will download and install
+the correct compiler version:
+
+```bash
+stack setup
+```
+
+## Running *GHCi*
+
+If you want to play with your solution in GHCi, just run the command:
+
+```bash
+stack ghci
+```
+
+## Feedback, Issues, Pull Requests
+
+The [exercism/haskell](https://github.com/exercism/haskell) repository on
+GitHub is the home for all of the Haskell exercises.
+
+If you have feedback about an exercise, or want to help implementing a new
+one, head over there and create an issue.  We'll do our best to help you!
+
+## Source
+
+All of Computer Science [http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-](http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
diff --git a/exercises/collatz-conjecture/examples/success-standard/package.yaml b/exercises/collatz-conjecture/examples/success-standard/package.yaml
new file mode 100644
index 000000000..26631e8d5
--- /dev/null
+++ b/exercises/collatz-conjecture/examples/success-standard/package.yaml
@@ -0,0 +1,16 @@
+name: collatz-conjecture
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: CollatzConjecture
+  source-dirs: src
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - collatz-conjecture
+      - hspec
diff --git a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
new file mode 100644
index 000000000..57288e268
--- /dev/null
+++ b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
@@ -0,0 +1,9 @@
+module CollatzConjecture (collatz) where
+
+collatzHelper :: Integer -> Integer -> Integer
+collatzHelper t x | x == 1    = t
+                  | even x    = collatzHelper (t+1) (x `div` 2)
+                  | otherwise = collatzHelper (t+1) (x*3 + 1)
+
+collatz :: Integer -> Integer
+collatz = collatzHelper 0
diff --git a/exercises/collatz-conjecture/package.yaml b/exercises/collatz-conjecture/package.yaml
new file mode 100644
index 000000000..a7524b4c1
--- /dev/null
+++ b/exercises/collatz-conjecture/package.yaml
@@ -0,0 +1,21 @@
+
+name: collatz-conjecture
+version: 1.0.0.3
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: CollatzConjecture
+  source-dirs: src
+  dependencies:
+  # - foo       # List here the packages you
+  # - bar       # want to use in your solution.
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - collatz-conjecture
+      - hspec
diff --git a/exercises/collatz-conjecture/src/CollatzConjectre.hs b/exercises/collatz-conjecture/src/CollatzConjectre.hs
new file mode 100644
index 000000000..1494deb79
--- /dev/null
+++ b/exercises/collatz-conjecture/src/CollatzConjectre.hs
@@ -0,0 +1,4 @@
+module CollatzConjecture (collatz) where
+
+collatz :: Integer -> Integer
+collatz = error "You need to implement this function."
diff --git a/exercises/collatz-conjecture/stack.yaml b/exercises/collatz-conjecture/stack.yaml
new file mode 100644
index 000000000..10da6ea9e
--- /dev/null
+++ b/exercises/collatz-conjecture/stack.yaml
@@ -0,0 +1 @@
+resolver: lts-8.21
diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
new file mode 100644
index 000000000..a4570fa44
--- /dev/null
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -0,0 +1,59 @@
+{-# OPTIONS_GHC -fno-warn-type-defaults #-}
+{-# LANGUAGE RecordWildCards #-}
+
+import Data.Foldable     (for_)
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
+
+import CollatzConjecture (collatz)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "collatz" $ for_ cases test
+  where
+
+    test Case{..} = it description assertion
+      where
+        assertion = collatz number `shouldBe` fromIntegral expected
+
+
+data Case = Case { description :: String
+                 , number      :: Integer
+                 , expected    :: Integer
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "collatz 1 don't require any steps."
+               , binary      = 1
+               , expected    = 0
+               }
+        , Case { description = "collatz 2 require 1 step."
+               , binary      = 2
+               , expected    = 1
+               }
+        , Case { description = "collatz 3 require 7 steps."
+               , binary      = 3
+               , expected    = 7
+               }
+        , Case { description = "collatz 4 require 2 steps."
+               , binary      = 4
+               , expected    = 2
+               }
+        , Case { description = "collatz 5 require 5 steps."
+               , binary      = 5
+               , expected    = 5
+               }
+        , Case { description = "collatz 6 require 8 steps."
+               , binary      = 6
+               , expected    = 8
+               }
+        , Case { description = "collatz 7 require 16 steps."
+               , binary      = 7
+               , expected    = 16
+               }
+        , Case { description = "collatz 666 require 113 steps."
+               , binary      = 666
+               , expected    = 113
+        ]

From 319fdfa5a45ee93306ab89ca0d53b5821a70e3a7 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 21:35:08 -0300
Subject: [PATCH 02/16] collatz-conjecture added to config.json

---
 config.json | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/config.json b/config.json
index 3b53b152d..deb31cfe3 100644
--- a/config.json
+++ b/config.json
@@ -58,6 +58,15 @@
       "topics": [
       ]
     },
+    {
+      "uuid": "6eba4eac-8395-4ad6-ac21-3651a11ab4b4",
+      "slug": "collatz-conjecture",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 1,
+      "topics": [
+      ]
+    },
     {
       "uuid": "85d77b8e-9b87-4d02-9fba-81f843bd66f1",
       "slug": "rna-transcription",

From b24814762a012b1c412b18baa83ba3028ca0c147 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 21:50:46 -0300
Subject: [PATCH 03/16] adding collatz-conjecture

---
 exercises/collatz-conjecture/test/Tests.hs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
index a4570fa44..be8d8fcac 100644
--- a/exercises/collatz-conjecture/test/Tests.hs
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -56,4 +56,5 @@ cases = [ Case { description = "collatz 1 don't require any steps."
         , Case { description = "collatz 666 require 113 steps."
                , binary      = 666
                , expected    = 113
+               }
         ]

From d353964ff3e6457a8b0a743d2eb3e195148c06d9 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 22:09:46 -0300
Subject: [PATCH 04/16] collatz conjecture

---
 exercises/collatz-conjecture/test/Tests.hs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
index be8d8fcac..0c1d2dbcf 100644
--- a/exercises/collatz-conjecture/test/Tests.hs
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -26,35 +26,35 @@ data Case = Case { description :: String
 
 cases :: [Case]
 cases = [ Case { description = "collatz 1 don't require any steps."
-               , binary      = 1
+               , number      = 1
                , expected    = 0
                }
         , Case { description = "collatz 2 require 1 step."
-               , binary      = 2
+               , number     = 2
                , expected    = 1
                }
         , Case { description = "collatz 3 require 7 steps."
-               , binary      = 3
+               , number     = 3
                , expected    = 7
                }
         , Case { description = "collatz 4 require 2 steps."
-               , binary      = 4
+               , number      = 4
                , expected    = 2
                }
         , Case { description = "collatz 5 require 5 steps."
-               , binary      = 5
+               , number      = 5
                , expected    = 5
                }
         , Case { description = "collatz 6 require 8 steps."
-               , binary      = 6
+               , number      = 6
                , expected    = 8
                }
         , Case { description = "collatz 7 require 16 steps."
-               , binary      = 7
+               , number      = 7
                , expected    = 16
                }
         , Case { description = "collatz 666 require 113 steps."
-               , binary      = 666
+               , number      = 666
                , expected    = 113
                }
         ]

From 8d850ca7e22a017e97af6ddeeeef564076c61918 Mon Sep 17 00:00:00 2001
From: Lucas Polymeris <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 22:25:29 -0300
Subject: [PATCH 05/16] Update README.md

---
 exercises/collatz-conjecture/README.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/exercises/collatz-conjecture/README.md b/exercises/collatz-conjecture/README.md
index 8ad146254..e0c6b62c5 100644
--- a/exercises/collatz-conjecture/README.md
+++ b/exercises/collatz-conjecture/README.md
@@ -79,7 +79,8 @@ one, head over there and create an issue.  We'll do our best to help you!
 
 ## Source
 
-All of Computer Science [http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-](http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-)
+An unsolved problem in mathematics named after mathematician Lothar Collatz
+see more at [collatz conjecture wikipedia]("https://en.wikipedia.org/wiki/3x_%2B_1_problem")
 
 ## Submitting Incomplete Solutions
 It's possible to submit an incomplete solution so you can see how others have completed the exercise.

From e99495fbabce719424b1e559084fb41e3af98272 Mon Sep 17 00:00:00 2001
From: Lucas Polymeris <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 22:25:58 -0300
Subject: [PATCH 06/16] Update package.yaml


From 80f3376abbbb038404d476577906f2e7896b5767 Mon Sep 17 00:00:00 2001
From: Lucas Polymeris <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 22:27:10 -0300
Subject: [PATCH 07/16] Update package.yaml

---
 exercises/collatz-conjecture/package.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/exercises/collatz-conjecture/package.yaml b/exercises/collatz-conjecture/package.yaml
index a7524b4c1..d786ca4fa 100644
--- a/exercises/collatz-conjecture/package.yaml
+++ b/exercises/collatz-conjecture/package.yaml
@@ -1,6 +1,6 @@
 
 name: collatz-conjecture
-version: 1.0.0.3
+version: 1.1.1
 
 dependencies:
   - base

From 4f97913201bf403e432b5f8ec874c6d314094d5f Mon Sep 17 00:00:00 2001
From: Lucas Polymeris <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 22:28:12 -0300
Subject: [PATCH 08/16] Update package.yaml

---
 exercises/collatz-conjecture/package.yaml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/exercises/collatz-conjecture/package.yaml b/exercises/collatz-conjecture/package.yaml
index d786ca4fa..955a30369 100644
--- a/exercises/collatz-conjecture/package.yaml
+++ b/exercises/collatz-conjecture/package.yaml
@@ -1,4 +1,3 @@
-
 name: collatz-conjecture
 version: 1.1.1
 

From c8cfb11c007ca85bf0c191143ad913aa4b8206f0 Mon Sep 17 00:00:00 2001
From: Lucas Polymeris <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 22:44:42 -0300
Subject: [PATCH 09/16] Update package.yaml

---
 exercises/collatz-conjecture/package.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/exercises/collatz-conjecture/package.yaml b/exercises/collatz-conjecture/package.yaml
index 955a30369..8b73186a7 100644
--- a/exercises/collatz-conjecture/package.yaml
+++ b/exercises/collatz-conjecture/package.yaml
@@ -1,5 +1,5 @@
 name: collatz-conjecture
-version: 1.1.1
+version: 1.1.1.1
 
 dependencies:
   - base

From 611ed615e557a155ad1a3238b7b510f7e392db49 Mon Sep 17 00:00:00 2001
From: Lucas Polymeris <lucaspolymeris@gmail.com>
Date: Mon, 18 Sep 2017 23:05:56 -0300
Subject: [PATCH 10/16] Update Tests.hs

---
 exercises/collatz-conjecture/test/Tests.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
index 0c1d2dbcf..a09447bfa 100644
--- a/exercises/collatz-conjecture/test/Tests.hs
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -30,11 +30,11 @@ cases = [ Case { description = "collatz 1 don't require any steps."
                , expected    = 0
                }
         , Case { description = "collatz 2 require 1 step."
-               , number     = 2
+               , number      = 2
                , expected    = 1
                }
         , Case { description = "collatz 3 require 7 steps."
-               , number     = 3
+               , number      = 3
                , expected    = 7
                }
         , Case { description = "collatz 4 require 2 steps."

From 492764c18ffcef6f248ac6affdbba1deaf579dd8 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Tue, 19 Sep 2017 13:05:54 -0300
Subject: [PATCH 11/16] name fixed

---
 .../src/{CollatzConjectre.hs => CollatzConjecture.hs}             | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename exercises/collatz-conjecture/src/{CollatzConjectre.hs => CollatzConjecture.hs} (100%)

diff --git a/exercises/collatz-conjecture/src/CollatzConjectre.hs b/exercises/collatz-conjecture/src/CollatzConjecture.hs
similarity index 100%
rename from exercises/collatz-conjecture/src/CollatzConjectre.hs
rename to exercises/collatz-conjecture/src/CollatzConjecture.hs

From d8c117076bdd94040dbae15bb1150687c18f7565 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Tue, 19 Sep 2017 15:02:02 -0300
Subject: [PATCH 12/16] new cases

---
 .../success-standard/src/CollatzConjecture.hs |  3 +-
 exercises/collatz-conjecture/test/Tests.hs    | 55 +++++++++----------
 2 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
index 57288e268..75377c76b 100644
--- a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
+++ b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
@@ -6,4 +6,5 @@ collatzHelper t x | x == 1    = t
                   | otherwise = collatzHelper (t+1) (x*3 + 1)
 
 collatz :: Integer -> Integer
-collatz = collatzHelper 0
+collatz x = if x <= 0 then error "Only positive numbers are allowed"
+                      else collatzHelper 0 x
diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
index a09447bfa..9446ee70f 100644
--- a/exercises/collatz-conjecture/test/Tests.hs
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -20,41 +20,40 @@ specs = describe "collatz" $ for_ cases test
 
 
 data Case = Case { description :: String
+                 , property    :: String
                  , number      :: Integer
                  , expected    :: Integer
                  }
 
 cases :: [Case]
-cases = [ Case { description = "collatz 1 don't require any steps."
+cases = [ Case { description = "zero steps for one"
+               , property    = "steps"
                , number      = 1
                , expected    = 0
                }
-        , Case { description = "collatz 2 require 1 step."
-               , number      = 2
-               , expected    = 1
-               }
-        , Case { description = "collatz 3 require 7 steps."
-               , number      = 3
-               , expected    = 7
-               }
-        , Case { description = "collatz 4 require 2 steps."
-               , number      = 4
-               , expected    = 2
-               }
-        , Case { description = "collatz 5 require 5 steps."
-               , number      = 5
-               , expected    = 5
-               }
-        , Case { description = "collatz 6 require 8 steps."
-               , number      = 6
-               , expected    = 8
-               }
-        , Case { description = "collatz 7 require 16 steps."
-               , number      = 7
-               , expected    = 16
-               }
-        , Case { description = "collatz 666 require 113 steps."
-               , number      = 666
-               , expected    = 113
+        , Case { description = "divide if even"
+               , property    = "steps"
+               , number      = 16
+               , expected    = 4
+               }
+        , Case { description = "even and odd steps"
+               , property    = "steps"
+               , number      = 12
+               , expected    = 9
+               }
+        , Case { description = "Large number of even and odd steps"
+               , property    = "steps"
+               , number      = 1000000
+               , expected    = 152
+               }
+        , Case { description = "zero is an error"
+               , property    = "steps"
+               , number      = 0
+               , expected    = error "Only positive numbers are allowed"
+               }
+        , Case { description = "negative value is an error"
+               , property    = "steps"
+               , number      = -15
+               , expected    = error "Only positive numbers are allowed"
                }
         ]

From 2ed3db67b14a1bf243f580e23ad1c36792d62bd1 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Tue, 19 Sep 2017 15:22:06 -0300
Subject: [PATCH 13/16] handling errors with Maybe

---
 .../success-standard/src/CollatzConjecture.hs    |  9 ++++-----
 exercises/collatz-conjecture/test/Tests.hs       | 16 ++++++++--------
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
index 75377c76b..1855e3495 100644
--- a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
+++ b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
@@ -1,10 +1,9 @@
 module CollatzConjecture (collatz) where
 
-collatzHelper :: Integer -> Integer -> Integer
-collatzHelper t x | x == 1    = t
+collatzHelper :: Integer -> Integer -> Maybe Integer
+collatzHelper t x | x == 1    = Just t
                   | even x    = collatzHelper (t+1) (x `div` 2)
                   | otherwise = collatzHelper (t+1) (x*3 + 1)
 
-collatz :: Integer -> Integer
-collatz x = if x <= 0 then error "Only positive numbers are allowed"
-                      else collatzHelper 0 x
+collatz :: Integer -> Maybe Integer
+collatz x = if  x <= 0 then Nothing else collatzHelper 0 x
diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
index 9446ee70f..22767bf64 100644
--- a/exercises/collatz-conjecture/test/Tests.hs
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -16,44 +16,44 @@ specs = describe "collatz" $ for_ cases test
 
     test Case{..} = it description assertion
       where
-        assertion = collatz number `shouldBe` fromIntegral expected
+        assertion = collatz number `shouldBe` expected
 
 
 data Case = Case { description :: String
                  , property    :: String
                  , number      :: Integer
-                 , expected    :: Integer
+                 , expected    :: Maybe Integer
                  }
 
 cases :: [Case]
 cases = [ Case { description = "zero steps for one"
                , property    = "steps"
                , number      = 1
-               , expected    = 0
+               , expected    = Just 0
                }
         , Case { description = "divide if even"
                , property    = "steps"
                , number      = 16
-               , expected    = 4
+               , expected    = Just 4
                }
         , Case { description = "even and odd steps"
                , property    = "steps"
                , number      = 12
-               , expected    = 9
+               , expected    =Just 9
                }
         , Case { description = "Large number of even and odd steps"
                , property    = "steps"
                , number      = 1000000
-               , expected    = 152
+               , expected    = Just 152
                }
         , Case { description = "zero is an error"
                , property    = "steps"
                , number      = 0
-               , expected    = error "Only positive numbers are allowed"
+               , expected    = Nothing
                }
         , Case { description = "negative value is an error"
                , property    = "steps"
                , number      = -15
-               , expected    = error "Only positive numbers are allowed"
+               , expected    = Nothing
                }
         ]

From 9061aeb486f487282c82915478c52387aba9a798 Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Tue, 19 Sep 2017 15:26:05 -0300
Subject: [PATCH 14/16] fix on src

---
 exercises/collatz-conjecture/src/CollatzConjecture.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/exercises/collatz-conjecture/src/CollatzConjecture.hs b/exercises/collatz-conjecture/src/CollatzConjecture.hs
index 1494deb79..239dff653 100644
--- a/exercises/collatz-conjecture/src/CollatzConjecture.hs
+++ b/exercises/collatz-conjecture/src/CollatzConjecture.hs
@@ -1,4 +1,4 @@
 module CollatzConjecture (collatz) where
 
-collatz :: Integer -> Integer
+collatz :: Integer -> Maybe Integer
 collatz = error "You need to implement this function."

From 14dfaeb755ded3e2b1fd36c3ca0fbf2427380d3e Mon Sep 17 00:00:00 2001
From: Average-user <lucaspolymeris@gmail.com>
Date: Tue, 19 Sep 2017 16:32:42 -0300
Subject: [PATCH 15/16] a few corrections

---
 config.json                                              | 1 +
 .../examples/success-standard/src/CollatzConjecture.hs   | 2 +-
 exercises/collatz-conjecture/test/Tests.hs               | 9 +--------
 3 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/config.json b/config.json
index deb31cfe3..da7dc2736 100644
--- a/config.json
+++ b/config.json
@@ -65,6 +65,7 @@
       "unlocked_by": null,
       "difficulty": 1,
       "topics": [
+        "Maybe"
       ]
     },
     {
diff --git a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
index 1855e3495..4a25404f9 100644
--- a/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
+++ b/exercises/collatz-conjecture/examples/success-standard/src/CollatzConjecture.hs
@@ -6,4 +6,4 @@ collatzHelper t x | x == 1    = Just t
                   | otherwise = collatzHelper (t+1) (x*3 + 1)
 
 collatz :: Integer -> Maybe Integer
-collatz x = if  x <= 0 then Nothing else collatzHelper 0 x
+collatz x = if x <= 0 then Nothing else collatzHelper 0 x
diff --git a/exercises/collatz-conjecture/test/Tests.hs b/exercises/collatz-conjecture/test/Tests.hs
index 22767bf64..ffeb293d2 100644
--- a/exercises/collatz-conjecture/test/Tests.hs
+++ b/exercises/collatz-conjecture/test/Tests.hs
@@ -20,39 +20,32 @@ specs = describe "collatz" $ for_ cases test
 
 
 data Case = Case { description :: String
-                 , property    :: String
                  , number      :: Integer
                  , expected    :: Maybe Integer
                  }
 
 cases :: [Case]
 cases = [ Case { description = "zero steps for one"
-               , property    = "steps"
                , number      = 1
                , expected    = Just 0
                }
         , Case { description = "divide if even"
-               , property    = "steps"
                , number      = 16
                , expected    = Just 4
                }
         , Case { description = "even and odd steps"
-               , property    = "steps"
                , number      = 12
-               , expected    =Just 9
+               , expected    = Just 9
                }
         , Case { description = "Large number of even and odd steps"
-               , property    = "steps"
                , number      = 1000000
                , expected    = Just 152
                }
         , Case { description = "zero is an error"
-               , property    = "steps"
                , number      = 0
                , expected    = Nothing
                }
         , Case { description = "negative value is an error"
-               , property    = "steps"
                , number      = -15
                , expected    = Nothing
                }

From 6c6484a2d11d48a6a30070860bb5f3c14757cfa3 Mon Sep 17 00:00:00 2001
From: Peter Tseng <pht24@cornell.edu>
Date: Tue, 19 Sep 2017 21:42:01 -0700
Subject: [PATCH 16/16] collatz: regenerate readme

---
 exercises/collatz-conjecture/README.md | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/exercises/collatz-conjecture/README.md b/exercises/collatz-conjecture/README.md
index e0c6b62c5..9e3533cd1 100644
--- a/exercises/collatz-conjecture/README.md
+++ b/exercises/collatz-conjecture/README.md
@@ -1,4 +1,4 @@
-## Collatz Conjecture.
+# Collatz Conjecture
 
 The Collatz Conjecture or 3x+1 problem can be summarized as follows:
 
@@ -25,6 +25,8 @@ Starting with n = 12, the steps would be as follows:
 
 Resulting in 9 steps. So for input n = 12, the return value would be 9.
 
+
+
 ## Getting Started
 
 For installation and learning resources, refer to the
@@ -79,8 +81,7 @@ one, head over there and create an issue.  We'll do our best to help you!
 
 ## Source
 
-An unsolved problem in mathematics named after mathematician Lothar Collatz
-see more at [collatz conjecture wikipedia]("https://en.wikipedia.org/wiki/3x_%2B_1_problem")
+An unsolved problem in mathematics named after mathematician Lothar Collatz [https://en.wikipedia.org/wiki/3x_%2B_1_problem](https://en.wikipedia.org/wiki/3x_%2B_1_problem)
 
 ## Submitting Incomplete Solutions
 It's possible to submit an incomplete solution so you can see how others have completed the exercise.