Implement Resistor Colors exercise

config.json

@@ -213,6 +213,16 @@
         "strings"
       ]
     },
+    {
+      "slug": "resistor-colors",
+      "uuid": "61be7bcd-42fb-44b7-a51d-1d081173f876",
+      "core": false,
+      "unlocked_by": "pangram",
+      "difficulty": 2,
+      "topics": [
+        "strings"
+      ]
+    },
     {
       "slug": "accumulate",
       "uuid": "5c5a9256-a55e-4bda-baf3-96d052732e11",

exercises/resistor-colors/README.md

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+# Resistor Colors
+
+If you want to build something using a Raspberry Pi, you'll probably use _resistors_. For this exercise, you need to know two things about them:
+
+* Each resistor has a resistance value.
+* Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
+To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values. Each band acts as a digit of a number. For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.
+
+In this exercise, you are going to create a helpful program so that you don't have to remember the values of the bands. The program will take two colors as input, and output the correct number.
+
+The band colors are encoded as follows:
+
+- Black: 0
+- Brown: 1
+- Red: 2
+- Orange: 3
+- Yellow: 4
+- Green: 5
+- Blue: 6
+- Violet: 7
+- Grey: 8
+- White: 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
+
+Maud de Vries, Erik Schierboom [https://github.com/exercism/problem-specifications/issues/1464](https://github.com/exercism/problem-specifications/issues/1464)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/resistor-colors/examples/success-standard/package.yaml

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+name: resistor-colors
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: ResistorColors
+  source-dirs: src
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - resistor-colors
+      - hspec

exercises/resistor-colors/examples/success-standard/src/ResistorColors.hs

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+module ResistorColors (Color(..), value) where
+
+data Color =
+    Black
+  | Brown
+  | Red
+  | Orange
+  | Yellow
+  | Green
+  | Blue
+  | Violet
+  | Grey
+  | White
+  deriving (Eq, Show, Read)
+
+convert :: Color -> Int
+convert Black = 0
+convert Brown = 1
+convert Red = 2
+convert Orange = 3
+convert Yellow = 4
+convert Green = 5
+convert Blue = 6
+convert Violet = 7
+convert Grey = 8
+convert White = 9
+
+value :: [Color] -> Int
+value = read . concatMap (show . convert)

exercises/resistor-colors/package.yaml

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+name: resistor-colors
+version: 1.0.0.0
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: ResistorColors
+  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:
+      - resistor-colors
+      - hspec

exercises/resistor-colors/src/ResistorColors.hs

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+module ResistorColors (Color(..), value) where
+
+data Color =
+    Black
+  | Brown
+  | Red
+  | Orange
+  | Yellow
+  | Green
+  | Blue
+  | Violet
+  | Grey
+  | White
+  deriving (Eq, Show, Read)
+
+value :: [Color] -> Int
+value cs = error "You need to implement this function."

exercises/resistor-colors/stack.yaml

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+resolver: lts-12.4

exercises/resistor-colors/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 ResistorColors (Color(..), value)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "value" $ for_ cases test
+  where
+
+    test Case{..} = it explanation assertion
+      where
+        explanation = unwords [show input, "-", description]
+        assertion   = value input `shouldBe` expected
+
+data Case = Case { description :: String
+                 , input       :: [Color]
+                 , expected    :: Int
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "Brown and black"
+               , input       = [Brown, Black]
+               , expected    = 10
+               }
+        , Case { description = "Blue and grey"
+               , input       = [Blue, Grey]
+               , expected    = 68
+               }
+        , Case { description = "Yellow and violet"
+               , input       = [Yellow, Violet]
+               , expected    = 47
+               }
+        , Case { description = "Orange and orange"
+               , input       = [Orange, Orange]
+               , expected    = 33
+               }
+        ]