dibs: I will implement exercise run-length-encoding

config.json

@@ -22,6 +22,12 @@
       "topics": [
       ]
     },
+    {
+      "slug": "run-length-encoding",
+      "difficulty": 1,
+      "topics": [
+      ]
+    },
     {
       "slug": "rna-transcription",
       "difficulty": 1,

exercises/run-length-encoding/examples/success-standard/package.yaml

@@ -0,0 +1,16 @@
+name: run-length-encoding
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: RunLength
+  source-dirs: src
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - run-length-encoding
+      - hspec

exercises/run-length-encoding/examples/success-standard/src/RunLength.hs

@@ -0,0 +1,21 @@
+module RunLength (decode, encode) where
+
+import Data.Char (isDigit)
+
+decode :: String -> String
+decode "" = ""
+decode s  = replicate n c ++ decode rest
+  where
+    i = takeWhile isDigit s
+    n = if null i then 1 else read i
+    c = head $ filter (not . isDigit) s
+    rest = drop (1 + length i) s
+
+encode :: String -> String
+encode "" = ""
+encode s  = i ++ c : encode rest
+  where
+    c = head s
+    l = length $ takeWhile (== c) s
+    i = if l == 1 then "" else show l
+    rest = drop l s

exercises/run-length-encoding/package.yaml

@@ -0,0 +1,19 @@
+name: run-length-encoding
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: RunLength
+  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:
+      - run-length-encoding
+      - hspec

exercises/run-length-encoding/src/RunLength.hs

@@ -0,0 +1,7 @@
+module RunLength (decode, encode) where
+
+decode :: String -> String
+decode = undefined
+
+encode :: String -> String
+encode = undefined

exercises/run-length-encoding/stack.yaml

@@ -0,0 +1 @@
+resolver: lts-7.9

exercises/run-length-encoding/test/Tests.hs

@@ -0,0 +1,75 @@
+{-# LANGUAGE RecordWildCards #-}
+
+import Data.Foldable     (for_)
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
+
+import RunLength (encode, decode)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "run-length-encoding" $ do
+          describe "decode" $ for_ decodeCases $ test decode
+          describe "encode" $ for_ encodeCases $ test encode
+          describe "both"   $ for_ bothCases   $ test (decode . encode)
+  where
+    test f Case{..} = it description $ f input `shouldBe` expected
+
+-- Test cases adapted from file
+-- `exercism/x-common/exercises/run-length-encoding/canonical-data.json`
+-- on 2016-12-26.
+
+data Case = Case { description :: String
+                 , input       :: String
+                 , expected    :: String
+                 }
+
+encodeCases :: [Case]
+encodeCases =
+    [ Case { description = "encode empty string"
+           , input       = ""
+           , expected    = ""
+           }
+    , Case { description = "encode single characters only"
+           , input       = "XYZ"
+           , expected    = "XYZ"
+           }
+    , Case { description = "encode simple"
+           , input       = "AABBBCCCC"
+           , expected    = "2A3B4C"
+           }
+    , Case { description = "encode with single values"
+           , input       = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
+           , expected    = "12WB12W3B24WB"
+           }
+    ]
+
+decodeCases :: [Case]
+decodeCases =
+    [ Case { description = "decode empty string"
+           , input       = ""
+           , expected    = ""
+           }
+    , Case { description = "decode single characters only"
+           , input       = "XYZ"
+           , expected    = "XYZ"
+           }
+    , Case { description = "decode simple"
+           , input       = "2A3B4C"
+           , expected    = "AABBBCCCC"
+           }
+    , Case { description = "decode with single values"
+           , input       = "12WB12W3B24WB"
+           , expected    = "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWB"
+           }
+    ]
+
+bothCases :: [Case]
+bothCases =
+    [ Case { description = "decode . encode combination"
+           , input       = "zzz ZZ  zZ"
+           , expected    = "zzz ZZ  zZ"
+           }
+    ]