Added CollatzConjecture

exercises/collatz-conjecture/CollatzConjecture.elm

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+module CollatzConjecture exposing (..)

exercises/collatz-conjecture/CollatzConjecture.example.elm

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+module CollatzConjecture exposing (collatz)
+
+
+collatz : Int -> Result String Int
+collatz start =
+    if start <= 0 then
+        Err "Only positive numbers are allowed"
+    else
+        Ok (collatzHelper 0 start)
+
+
+collatzHelper : Int ->  Int -> Int
+collatzHelper steps start =
+    if start == 1 then
+        steps
+    else if start % 2 == 0 then
+        collatzHelper (1 + steps) (start // 2)
+    else
+        collatzHelper (1 + steps) (3 * start + 1)

exercises/collatz-conjecture/elm-package.json

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+{
+    "version": "3.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/elm.git",
+    "license": "BSD3",
+    "source-directories": [
+        "."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "elm-lang/core": "5.0.0 <= v < 6.0.0"
+    },
+    "elm-version": "0.18.0 <= v < 0.19.0"
+}
+

exercises/collatz-conjecture/package.json

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+{
+    "description": "Exercism/Elm",
+    "repository": "https://github.com/exercism/elm.git",
+    "license": "MIT",
+    "scripts": {
+        "postinstall": "elm-package install -y",
+        "watch": "elm-test --watch",
+        "test": "elm-test"
+    },
+    "dependencies": {
+        "elm": "0.18.0",
+        "elm-test": "0.18.3"
+    }
+}

exercises/collatz-conjecture/tests/Tests.elm

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+module Tests exposing (..)
+
+import Test exposing (..)
+import Expect
+import CollatzConjecture exposing (collatz)
+
+
+tests : Test
+tests =
+    describe "CollatzConjecture tests"
+        [ test "zero steps for one" <|
+            \() ->
+                Expect.equal (Ok 0) (collatz 1)
+
+        -- Once you get the first test passing, remove the
+        -- `skip <|` (just leave the comma) on the next
+        -- lines to continue!
+
+        , skip <|
+            test "divide if even" <|
+            \() ->
+                Expect.equal (Ok 4) (collatz 16)
+        , skip <|
+            test "even and odd step" <|
+            \() ->
+                Expect.equal (Ok 9) (collatz 12)
+        , skip <|
+            test "Large number of even and odd step" <|
+            \() ->
+                Expect.equal (Ok 152) (collatz 1000000)
+        , skip <|
+            test "zero is an error" <|
+            \() ->
+                Expect.equal (Err "Only positive numbers are allowed") (collatz 0)
+        , skip <|
+            test "negative values is an error" <|
+            \() ->
+                Expect.equal (Err "Only positive numbers are allowed") (collatz -15)
+        ]

exercises/collatz-conjecture/tests/elm-package.json

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+{
+    "version": "3.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/elm.git",
+    "license": "BSD3",
+    "source-directories": [
+        ".",
+        ".."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "elm-lang/core": "5.0.0 <= v < 6.0.0",
+        "elm-community/elm-test": "4.0.0 <= v < 5.0.0"
+    },
+    "elm-version": "0.18.0 <= v < 0.19.0"
+}