Add armstrong-numbers

Author: koladilip

armstrong-numbers/README.md

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+# Armstrong Numbers
+
+An [Armstrong number](https://en.wikipedia.org/wiki/Narcissistic_number) is a number that is the sum of its own digits each raised to the power of the number of digits.
+
+For example:
+
+- 9 is an Armstrong number, because `9 = 9^1 = 9`
+- 10 is *not* an Armstrong number, because `10 != 1^2 + 0^2 = 1`
+- 153 is an Armstrong number, because: `153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`
+- 154 is *not* an Armstrong number, because: `154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`
+
+Write some code to determine whether a number is an Armstrong number.
+
+
+## Getting Started
+
+Please refer to the [installation](https://exercism.io/tracks/haskell/installation)
+and [learning](https://exercism.io/tracks/haskell/learning) help pages.
+
+## 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
+
+Wikipedia [https://en.wikipedia.org/wiki/Narcissistic_number](https://en.wikipedia.org/wiki/Narcissistic_number)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

armstrong-numbers/armstrong-numbers.cabal

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+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.33.0.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: a4833901b954a0a033311786494ec67c394a98266766e3173a879ad937a493d7
+
+name:           armstrong-numbers
+version:        1.1.0.3
+build-type:     Simple
+
+library
+  exposed-modules:
+      ArmstrongNumbers
+  other-modules:
+      Paths_armstrong_numbers
+  hs-source-dirs:
+      src
+  ghc-options: -Wall
+  build-depends:
+      base
+  default-language: Haskell2010
+
+test-suite test
+  type: exitcode-stdio-1.0
+  main-is: Tests.hs
+  other-modules:
+      Paths_armstrong_numbers
+  hs-source-dirs:
+      test
+  build-depends:
+      armstrong-numbers
+    , base
+    , hspec
+  default-language: Haskell2010

armstrong-numbers/package.yaml

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+name: armstrong-numbers
+version: 1.1.0.3
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: ArmstrongNumbers
+  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:
+      - armstrong-numbers
+      - hspec

armstrong-numbers/src/ArmstrongNumbers.hs

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+module ArmstrongNumbers (armstrong) where
+
+digits :: Integral a => a -> [a]
+digits n
+    | n < 10 = [n]
+    | otherwise = (rem n 10) : digits (div n 10)
+
+armstrong :: Integral a => a -> Bool
+armstrong n 
+    | n < 10 = True
+    | otherwise = (sum $ map (^l) digs) == n
+        where digs = digits n; l = length digs

armstrong-numbers/stack.yaml

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+resolver: lts-15.8

armstrong-numbers/stack.yaml.lock

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+# This file was autogenerated by Stack.
+# You should not edit this file by hand.
+# For more information, please see the documentation at:
+#   https://docs.haskellstack.org/en/stable/lock_files
+
+packages: []
+snapshots:
+- completed:
+    size: 492015
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/15/8.yaml
+    sha256: 926bc3d70249dd0ba05277ff00943c0addb35b627cb641752669e7cf771310d0
+  original: lts-15.8

armstrong-numbers/test/Tests.hs

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+{-# LANGUAGE RecordWildCards #-}
+
+import Data.Foldable     (for_)
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
+
+import ArmstrongNumbers (armstrong)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "armstrong" $ for_ cases test
+  where
+
+    test Case{..} = it description assertion
+      where
+        assertion = armstrong input `shouldBe` expected
+
+data Case = Case { description :: String
+                 , input       :: Int
+                 , expected    :: Bool
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "Zero is an Armstrong numbers"
+               , input       = 0
+               , expected    = True
+               } 
+        , Case { description = "Single digit numbers are Armstrong numbers"
+               , input       = 5
+               , expected    = True
+               }
+        , Case { description = "There are no 2 digit Armstrong numbers"
+               , input       = 10
+               , expected    = False
+               }
+        , Case { description = "Three digit number that is an Armstrong number"
+               , input       = 153
+               , expected    = True
+               }
+        , Case { description = "Three digit number that is not an Armstrong number"
+               , input       = 100
+               , expected    = False
+               }
+        , Case { description = "Four digit number that is an Armstrong number"
+               , input       = 9474
+               , expected    = True
+               }
+        , Case { description = "Four digit number that is not an Armstrong number"
+               , input       = 9475
+               , expected    = False
+               }
+        , Case { description = "Seven digit number that is an Armstrong number"
+               , input       = 9926315
+               , expected    = True
+               }
+        , Case { description = "Seven digit number that is not an Armstrong number"
+               , input       = 9926314
+               , expected    = False
+               }
+        ]