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haskell/roman-numerals/README.md

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+# Roman Numerals
+
+Write a function to convert from normal numbers to Roman Numerals.
+
+The Romans were a clever bunch. They conquered most of Europe and ruled
+it for hundreds of years. They invented concrete and straight roads and
+even bikinis. One thing they never discovered though was the number
+zero. This made writing and dating extensive histories of their exploits
+slightly more challenging, but the system of numbers they came up with
+is still in use today. For example the BBC uses Roman numerals to date
+their programmes.
+
+The Romans wrote numbers using letters - I, V, X, L, C, D, M. (notice
+these letters have lots of straight lines and are hence easy to hack
+into stone tablets).
+
+```text
+ 1  => I
+10  => X
+ 7  => VII
+```
+
+There is no need to be able to convert numbers larger than about 3000.
+(The Romans themselves didn't tend to go any higher)
+
+Wikipedia says: Modern Roman numerals ... are written by expressing each
+digit separately starting with the left most digit and skipping any
+digit with a value of zero.
+
+To see this in practice, consider the example of 1990.
+
+In Roman numerals 1990 is MCMXC:
+
+1000=M
+900=CM
+90=XC
+
+2008 is written as MMVIII:
+
+2000=MM
+8=VIII
+
+See also: http://www.novaroma.org/via_romana/numbers.html
+
+## Hints
+
+To complete this exercise you need to implement the function `numerals`,
+that *maybe* converts a number to a *string* representing a roman numeral.
+
+Your function is expected to, at least, convert numbers up to 3000,
+but is up to you to decide how far you want to go.
+
+
+
+## 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
+
+The Roman Numeral Kata [http://codingdojo.org/cgi-bin/index.pl?KataRomanNumerals](http://codingdojo.org/cgi-bin/index.pl?KataRomanNumerals)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

haskell/roman-numerals/package.yaml

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+name: roman-numerals
+version: 1.2.0.5
+
+dependencies:
+  - base
+
+library:
+  exposed-modules: Roman
+  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:
+      - roman-numerals
+      - hspec

haskell/roman-numerals/src/Roman.hs

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+module Roman (numerals) where
+
+numerals :: Integer -> Maybe String
+numerals n = error "You need to implement this function."

haskell/roman-numerals/stack.yaml

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+resolver: lts-11.1

haskell/roman-numerals/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 Roman (numerals)
+
+main :: IO ()
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "numerals" $ for_ cases test
+  where
+
+    test Case{..} = it explanation assertion
+      where
+        explanation = show number ++ ": " ++ description
+        assertion   = numerals (fromIntegral number) `shouldBe` expected
+
+data Case = Case { description :: String
+                 , number      :: Integer
+                 , expected    :: Maybe String
+                 }
+
+cases :: [Case]
+cases = [ Case { description = "1 is a single I"
+               , number      = 1
+               , expected    = Just "I"
+               }
+        , Case { description = "2 is two I's"
+               , number      = 2
+               , expected    = Just "II"
+               }
+        , Case { description = "3 is three I's"
+               , number      = 3
+               , expected    = Just "III"
+               }
+        , Case { description = "4, being 5 - 1, is IV"
+               , number      = 4
+               , expected    = Just "IV"
+               }
+        , Case { description = "5 is a single V"
+               , number      = 5
+               , expected    = Just "V"
+               }
+        , Case { description = "6, being 5 + 1, is VI"
+               , number      = 6
+               , expected    = Just "VI"
+               }
+        , Case { description = "9, being 10 - 1, is IX"
+               , number      = 9
+               , expected    = Just "IX"
+               }
+        , Case { description = "20 is two X's"
+               , number      = 27
+               , expected    = Just "XXVII"
+               }
+        , Case { description = "48 is not 50 - 2 but rather 40 + 8"
+               , number      = 48
+               , expected    = Just "XLVIII"
+               }
+        , Case { description = "49 is not 40 + 5 + 4 but rather 50 - 10 + 10 - 1"
+               , number      = 49
+               , expected    = Just "XLIX"
+               }
+        , Case { description = "50 is a single L"
+               , number      = 59
+               , expected    = Just "LIX"
+               }
+        , Case { description = "90, being 100 - 10, is XC"
+               , number      = 93
+               , expected    = Just "XCIII"
+               }
+        , Case { description = "100 is a single C"
+               , number      = 141
+               , expected    = Just "CXLI"
+               }
+        , Case { description = "60, being 50 + 10, is LX"
+               , number      = 163
+               , expected    = Just "CLXIII"
+               }
+        , Case { description = "400, being 500 - 100, is CD"
+               , number      = 402
+               , expected    = Just "CDII"
+               }
+        , Case { description = "500 is a single D"
+               , number      = 575
+               , expected    = Just "DLXXV"
+               }
+        , Case { description = "900, being 1000 - 100, is CM"
+               , number      = 911
+               , expected    = Just "CMXI"
+               }
+        , Case { description = "1000 is a single M"
+               , number      = 1024
+               , expected    = Just "MXXIV"
+               }
+        , Case { description = "3000 is three M's"
+               , number      = 3000
+               , expected    = Just "MMM"
+               }
+        ]