✅ haskell: collatz-conjecture

haskell/collatz-conjecture/HELP.md

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+# Help
+
+## 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
+```
+
+or
+
+```
+RedownloadInvalidResponse Request {
+...
+}
+ "/home/username/.stack/build-plan/lts-xx.yy.yaml" (Response {responseStatus = Status {statusCode = 404, statusMessage = "Not Found"},
+```
+
+You are probably running an old stack version and need
+to upgrade it. Try running:
+
+```bash
+stack upgrade
+```
+
+Or see other options for upgrading at [Stack documentation](https://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade).
+
+#### 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
+```
+
+
+If you want to play with your solution in GHCi, just run the command:
+
+```bash
+stack ghci
+```
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit src/CollatzConjecture.hs` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Haskell track's documentation](https://exercism.org/docs/tracks/haskell)
+- [Exercism's support channel on gitter](https://gitter.im/exercism/support)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+## Getting Started
+
+Please refer to the [installation](https://exercism.io/tracks/haskell/installation)
+and [learning](https://exercism.io/tracks/haskell/learning) help pages.
+
+## 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!
+{{ with .Spec.Credits }}

haskell/collatz-conjecture/README.md

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+# Collatz Conjecture
+
+Welcome to Collatz Conjecture on Exercism's Haskell Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+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.
+
+## Source
+
+### Contributed to by
+
+- @guygastineau
+- @iHiD
+- @navossoc
+- @petertseng
+- @ppartarr
+- @sshine
+- @tejasbubane
+
+### Based on
+
+An unsolved problem in mathematics named after mathematician Lothar Collatz - https://en.wikipedia.org/wiki/3x_%2B_1_problem

haskell/collatz-conjecture/examples/success-standard/package.yaml

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+name: collatz-conjecture
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: CollatzConjecture
+  source-dirs: src
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - collatz-conjecture
+      - hspec

haskell/collatz-conjecture/package.yaml

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+name: collatz-conjecture
+version: 1.2.1.4
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: CollatzConjecture
+  source-dirs: src
+  ghc-options: -Wall
+  # 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

haskell/collatz-conjecture/src/CollatzConjecture.hs

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+module CollatzConjecture (collatz) where
+
+collatz :: Integer -> Maybe Integer
+collatz n = if n <= 0 then Nothing else step 0 n
+
+step :: Integer -> Integer -> Maybe Integer
+step count n
+  | n == 1     = Just count
+  | even n     = step (count + 1) (n `div` 2)
+  | otherwise  = step (count + 1) (3 * n + 1)

haskell/collatz-conjecture/stack.yaml

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+resolver: lts-16.21

haskell/collatz-conjecture/test/Tests.hs

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+{-# 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` expected
+
+
+data Case = Case { description :: String
+                 , number      :: Integer
+                 , expected    :: Maybe Integer
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "zero steps for one"
+               , number      = 1
+               , expected    = Just 0
+               }
+        , Case { description = "divide if even"
+               , number      = 16
+               , expected    = Just 4
+               }
+        , Case { description = "even and odd steps"
+               , number      = 12
+               , expected    = Just 9
+               }
+        , Case { description = "large number of even and odd steps"
+               , number      = 1000000
+               , expected    = Just 152
+               }
+        , Case { description = "zero is an error"
+               , number      = 0
+               , expected    = Nothing
+               }
+        , Case { description = "negative value is an error"
+               , number      = -15
+               , expected    = Nothing
+               }
+        ]
+
+-- 553e2f7a6ce638a6cf622985b9138e6013626eb3