[Haskell] Added Proverb solution

Author: MTRecouso

haskell/proverb/README.md

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+# Proverb
+
+For want of a horseshoe nail, a kingdom was lost, or so the saying goes.
+
+Given a list of inputs, generate the relevant proverb. For example, given the list `["nail", "shoe", "horse", "rider", "message", "battle", "kingdom"]`, you will output the full text of this proverbial rhyme:
+
+```text
+For want of a nail the shoe was lost.
+For want of a shoe the horse was lost.
+For want of a horse the rider was lost.
+For want of a rider the message was lost.
+For want of a message the battle was lost.
+For want of a battle the kingdom was lost.
+And all for the want of a nail.
+```
+
+Note that the list of inputs may vary; your solution should be able to handle lists of arbitrary length and content. No line of the output text should be a static, unchanging string; all should vary according to the input given.
+
+
+## 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 [http://en.wikipedia.org/wiki/For_Want_of_a_Nail](http://en.wikipedia.org/wiki/For_Want_of_a_Nail)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

haskell/proverb/package.yaml

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+name: proverb
+version: 1.1.0.2
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: Proverb
+  source-dirs: src
+  ghc-options: -Wall
+
+tests:
+  test:
+    main: Tests.hs
+    source-dirs: test
+    dependencies:
+      - proverb
+      - hspec

haskell/proverb/proverb.cabal

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+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.31.1.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: 7daafeec8a2dd49fabe794a5696bd6a30f4acc5b1e9a395f632316e692f0fcb8
+
+name:           proverb
+version:        1.1.0.2
+build-type:     Simple
+
+library
+  exposed-modules:
+      Proverb
+  other-modules:
+      Paths_proverb
+  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_proverb
+  hs-source-dirs:
+      test
+  build-depends:
+      base
+    , hspec
+    , proverb
+  default-language: Haskell2010

haskell/proverb/src/Proverb.hs

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+module Proverb(recite) where
+
+recite :: [String] -> String
+recite [] = ""
+recite [item] = reciteConclusion item
+recite items = reciteReasoning items ++ reciteConclusion (head items)
+
+
+reciteReasoning :: [String] -> String
+reciteReasoning [] = ""
+reciteReasoning [_] = ""
+reciteReasoning (item : nextItem : remainingItems) = 
+    "For want of a " ++ item ++ " the " ++ nextItem ++ " was lost.\n" 
+    ++ reciteReasoning ([nextItem] ++ remainingItems)
+
+
+reciteConclusion :: String -> String
+reciteConclusion item = "And all for the want of a " ++ item ++ "."

haskell/proverb/stack.yaml

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+resolver: lts-14.7

haskell/proverb/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 Data.List (intercalate)
+
+import Proverb (recite)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "recite" $ for_ cases test
+  where
+
+    test Case{..} = it description assertion
+      where
+        assertion = recite input `shouldBe` expected
+
+
+data Case = Case { description :: String
+                 , input       :: [String]
+                 , expected    :: String
+                 }
+
+joinLines :: [String] -> String
+joinLines = intercalate "\n"
+
+cases :: [Case]
+cases = [ Case { description = "zero pieces"
+               , input       = []
+               , expected    = ""
+               }
+        , Case { description = "one piece"
+               , input       = ["nail"]
+               , expected    = "And all for the want of a nail."
+               }
+        , Case { description = "two pieces"
+               , input       = ["nail", "shoe"]
+               , expected    =
+                   joinLines [ "For want of a nail the shoe was lost."
+                             , "And all for the want of a nail."
+                             ]
+               }
+        , Case { description = "three pieces"
+               , input       = ["nail", "shoe", "horse"]
+               , expected    =
+                   joinLines [ "For want of a nail the shoe was lost."
+                             , "For want of a shoe the horse was lost."
+                             , "And all for the want of a nail."
+                             ]
+               }
+        , Case { description = "full proverb"
+               , input       = [ "nail"
+                               , "shoe"
+                               , "horse"
+                               , "rider"
+                               , "message"
+                               , "battle"
+                               , "kingdom"
+                               ]
+               , expected    =
+                 joinLines [ "For want of a nail the shoe was lost."
+                           , "For want of a shoe the horse was lost."
+                           , "For want of a horse the rider was lost."
+                           , "For want of a rider the message was lost."
+                           , "For want of a message the battle was lost."
+                           , "For want of a battle the kingdom was lost."
+                           , "And all for the want of a nail."
+                           ]
+               }
+        , Case { description = "four pieces modernized"
+               , input       = ["pin", "gun", "soldier", "battle"]
+               , expected    =
+                 joinLines [ "For want of a pin the gun was lost."
+                           , "For want of a gun the soldier was lost."
+                           , "For want of a soldier the battle was lost."
+                           , "And all for the want of a pin."
+                           ]
+               }
+        ]