From 02aaccf8ae54471e93678e0ee65e5c2362b15360 Mon Sep 17 00:00:00 2001
From: rbasso <rbasso@sharpgeeks.net>
Date: Tue, 20 Sep 2016 15:22:46 +0900
Subject: [PATCH] roman-numerals: Change return type to a Maybe

- Change test suite to expect a `Maybe`.
- Add `HINTS.md` do explain what is expected in a solution.
- Patch the example solution to return `Just` values.
---
 exercises/roman-numerals/HINTS.md       |  7 +++++
 exercises/roman-numerals/src/Example.hs |  4 +--
 exercises/roman-numerals/test/Tests.hs  | 38 ++++++++++++-------------
 3 files changed, 28 insertions(+), 21 deletions(-)
 create mode 100644 exercises/roman-numerals/HINTS.md

diff --git a/exercises/roman-numerals/HINTS.md b/exercises/roman-numerals/HINTS.md
new file mode 100644
index 000000000..66985265c
--- /dev/null
+++ b/exercises/roman-numerals/HINTS.md
@@ -0,0 +1,7 @@
+## 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.
diff --git a/exercises/roman-numerals/src/Example.hs b/exercises/roman-numerals/src/Example.hs
index e0254b8b4..12e5a2851 100644
--- a/exercises/roman-numerals/src/Example.hs
+++ b/exercises/roman-numerals/src/Example.hs
@@ -1,7 +1,7 @@
 module Roman (numerals) where
 
-numerals :: Int -> String
-numerals = go numeralMap
+numerals :: Int -> Maybe String
+numerals = Just . go numeralMap
   where
     go pairs@((value, digits):pairs') n
       | n >= value = digits ++ go pairs (n - value)
diff --git a/exercises/roman-numerals/test/Tests.hs b/exercises/roman-numerals/test/Tests.hs
index 23d930863..702a24a42 100644
--- a/exercises/roman-numerals/test/Tests.hs
+++ b/exercises/roman-numerals/test/Tests.hs
@@ -23,62 +23,62 @@ specs = describe "roman-numerals" $
 -- Test cases adapted from `exercism/x-common/roman-numerals.json` on 2016-07-26.
 
 data Case = Case { number   :: Integer
-                 , expected :: String
+                 , expected :: Maybe String
                  }
 
 cases :: [Case]
 cases = [ Case { number   = 1
-               , expected = "I"
+               , expected = Just "I"
                }
         , Case { number   = 2
-               , expected = "II"
+               , expected = Just "II"
                }
         , Case { number   = 3
-               , expected = "III"
+               , expected = Just "III"
                }
         , Case { number   = 4
-               , expected = "IV"
+               , expected = Just "IV"
                }
         , Case { number   = 5
-               , expected = "V"
+               , expected = Just "V"
                }
         , Case { number   = 6
-               , expected = "VI"
+               , expected = Just "VI"
                }
         , Case { number   = 9
-               , expected = "IX"
+               , expected = Just "IX"
                }
         , Case { number   = 27
-               , expected = "XXVII"
+               , expected = Just "XXVII"
                }
         , Case { number   = 48
-               , expected = "XLVIII"
+               , expected = Just "XLVIII"
                }
         , Case { number   = 59
-               , expected = "LIX"
+               , expected = Just "LIX"
                }
         , Case { number   = 93
-               , expected = "XCIII"
+               , expected = Just "XCIII"
                }
         , Case { number   = 141
-               , expected = "CXLI"
+               , expected = Just "CXLI"
                }
         , Case { number   = 163
-               , expected = "CLXIII"
+               , expected = Just "CLXIII"
                }
         , Case { number   = 402
-               , expected = "CDII"
+               , expected = Just "CDII"
                }
         , Case { number   = 575
-               , expected = "DLXXV"
+               , expected = Just "DLXXV"
                }
         , Case { number   = 911
-               , expected = "CMXI"
+               , expected = Just "CMXI"
                }
         , Case { number   = 1024
-               , expected = "MXXIV"
+               , expected = Just "MXXIV"
                }
         , Case { number   = 3000
-               , expected = "MMM"
+               , expected = Just "MMM"
                }
         ]