Add new practice exercise dnd-character (#549)

* Add new practice exercise `dnd-character`

* Number format

* Add tests about ditribution

* Update elm.json

* Refactor adding hitpoints

* Precompute generated values

* Use fuzz tests

* tweak number of runs

* Use fuzz whenever possible

* simplify hitpoint

* run time must be an integer

config.json

@@ -1206,6 +1206,17 @@
           "pattern-matching"
         ],
         "difficulty": 3
+      },
+      {
+        "slug": "dnd-character",
+        "name": "D&D Character",
+        "uuid": "c22b805f-36db-407c-92d1-39ba0e4fa041",
+        "practices": [],
+        "prerequisites": [
+          "lists",
+          "records"
+        ],
+        "difficulty": 5
       }
     ]
   }

exercises/practice/dnd-character/.docs/instructions.md

@@ -0,0 +1,31 @@
+# Instructions
+
+For a game of [Dungeons & Dragons][dnd], each player starts by generating a character they can play with.
+This character has, among other things, six abilities; strength, dexterity, constitution, intelligence, wisdom and charisma.
+These six abilities have scores that are determined randomly.
+You do this by rolling four 6-sided dice and record the sum of the largest three dice.
+You do this six times, once for each ability.
+
+Your character's initial hitpoints are 10 + your character's constitution modifier.
+You find your character's constitution modifier by subtracting 10 from your character's constitution, divide by 2 and round down.
+
+Write a random character generator that follows the rules above.
+
+For example, the six throws of four dice may look like:
+
+- 5, 3, 1, 6: You discard the 1 and sum 5 + 3 + 6 = 14, which you assign to strength.
+- 3, 2, 5, 3: You discard the 2 and sum 3 + 5 + 3 = 11, which you assign to dexterity.
+- 1, 1, 1, 1: You discard the 1 and sum 1 + 1 + 1 = 3, which you assign to constitution.
+- 2, 1, 6, 6: You discard the 1 and sum 2 + 6 + 6 = 14, which you assign to intelligence.
+- 3, 5, 3, 4: You discard the 3 and sum 5 + 3 + 4 = 12, which you assign to wisdom.
+- 6, 6, 6, 6: You discard the 6 and sum 6 + 6 + 6 = 18, which you assign to charisma.
+
+Because constitution is 3, the constitution modifier is -4 and the hitpoints are 6.
+
+## Notes
+
+Most programming languages feature (pseudo-)random generators, but few programming languages are designed to roll dice.
+One such language is [Troll][troll].
+
+[dnd]: https://en.wikipedia.org/wiki/Dungeons_%26_Dragons
+[troll]: https://di.ku.dk/Ansatte/?pure=da%2Fpublications%2Ftroll-a-language-for-specifying-dicerolls(84a45ff0-068b-11df-825d-000ea68e967b)%2Fexport.html

exercises/practice/dnd-character/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "jiegillet"
+  ],
+  "files": {
+    "solution": [
+      "src/DndCharacter.elm"
+    ],
+    "test": [
+      "tests/Tests.elm"
+    ],
+    "example": [
+      ".meta/src/DndCharacter.example.elm"
+    ]
+  },
+  "blurb": "Randomly generate Dungeons & Dragons characters.",
+  "source": "Simon Shine, Erik Schierboom",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/616#issuecomment-437358945"
+}

exercises/practice/dnd-character/.meta/src/DndCharacter.example.elm

@@ -0,0 +1,52 @@
+module DndCharacter exposing (Character, ability, character, modifier)
+
+import Random exposing (Generator)
+
+
+type alias Character =
+    { strength : Int
+    , dexterity : Int
+    , constitution : Int
+    , intelligence : Int
+    , wisdom : Int
+    , charisma : Int
+    , hitpoints : Int
+    }
+
+
+modifier : Int -> Int
+modifier score =
+    floor ((toFloat score - 10) / 2)
+
+
+ability : Generator Int
+ability =
+    let
+        sumOfMaxThree =
+            List.sort >> List.reverse >> List.take 3 >> List.sum
+    in
+    Random.list 4 (Random.int 1 6)
+        |> Random.map sumOfMaxThree
+
+
+character : Generator Character
+character =
+    Random.constant Character
+        |> apply ability
+        |> apply ability
+        |> apply ability
+        |> apply ability
+        |> apply ability
+        |> apply ability
+        |> apply (Random.constant 0)
+        |> Random.map fixHitpoints
+
+
+apply : Generator a -> Generator (a -> b) -> Generator b
+apply genA =
+    Random.andThen (\aToB -> Random.map aToB genA)
+
+
+fixHitpoints : Character -> Character
+fixHitpoints ({ constitution } as zeroHpCharacter) =
+    { zeroHpCharacter | hitpoints = 10 + modifier constitution }

exercises/practice/dnd-character/.meta/tests.toml

@@ -0,0 +1,69 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[1e9ae1dc-35bd-43ba-aa08-e4b94c20fa37]
+description = "ability modifier -> ability modifier for score 3 is -4"
+
+[cc9bb24e-56b8-4e9e-989d-a0d1a29ebb9c]
+description = "ability modifier -> ability modifier for score 4 is -3"
+
+[5b519fcd-6946-41ee-91fe-34b4f9808326]
+description = "ability modifier -> ability modifier for score 5 is -3"
+
+[dc2913bd-6d7a-402e-b1e2-6d568b1cbe21]
+description = "ability modifier -> ability modifier for score 6 is -2"
+
+[099440f5-0d66-4b1a-8a10-8f3a03cc499f]
+description = "ability modifier -> ability modifier for score 7 is -2"
+
+[cfda6e5c-3489-42f0-b22b-4acb47084df0]
+description = "ability modifier -> ability modifier for score 8 is -1"
+
+[c70f0507-fa7e-4228-8463-858bfbba1754]
+description = "ability modifier -> ability modifier for score 9 is -1"
+
+[6f4e6c88-1cd9-46a0-92b8-db4a99b372f7]
+description = "ability modifier -> ability modifier for score 10 is 0"
+
+[e00d9e5c-63c8-413f-879d-cd9be9697097]
+description = "ability modifier -> ability modifier for score 11 is 0"
+
+[eea06f3c-8de0-45e7-9d9d-b8cab4179715]
+description = "ability modifier -> ability modifier for score 12 is +1"
+
+[9c51f6be-db72-4af7-92ac-b293a02c0dcd]
+description = "ability modifier -> ability modifier for score 13 is +1"
+
+[94053a5d-53b6-4efc-b669-a8b5098f7762]
+description = "ability modifier -> ability modifier for score 14 is +2"
+
+[8c33e7ca-3f9f-4820-8ab3-65f2c9e2f0e2]
+description = "ability modifier -> ability modifier for score 15 is +2"
+
+[c3ec871e-1791-44d0-b3cc-77e5fb4cd33d]
+description = "ability modifier -> ability modifier for score 16 is +3"
+
+[3d053cee-2888-4616-b9fd-602a3b1efff4]
+description = "ability modifier -> ability modifier for score 17 is +3"
+
+[bafd997a-e852-4e56-9f65-14b60261faee]
+description = "ability modifier -> ability modifier for score 18 is +4"
+
+[4f28f19c-2e47-4453-a46a-c0d365259c14]
+description = "random ability is within range"
+
+[385d7e72-864f-4e88-8279-81a7d75b04ad]
+description = "random character is valid"
+
+[2ca77b9b-c099-46c3-a02c-0d0f68ffa0fe]
+description = "each ability is only calculated once"
+include = false
+comment = "This does not make sense for Elm's Random.Generator"

exercises/practice/dnd-character/elm.json

@@ -0,0 +1,29 @@
+{
+    "type": "application",
+    "source-directories": [
+        "src"
+    ],
+    "elm-version": "0.19.1",
+    "dependencies": {
+        "direct": {
+            "elm/core": "1.0.5",
+            "elm/json": "1.1.3",
+            "elm/parser": "1.1.0",
+            "elm/random": "1.0.0",
+            "elm/regex": "1.0.0",
+            "elm/time": "1.0.0"
+        },
+        "indirect": {}
+    },
+    "test-dependencies": {
+        "direct": {
+            "elm-explorations/test": "2.1.0",
+            "rtfeldman/elm-iso8601-date-strings": "1.1.4"
+        },
+        "indirect": {
+            "elm/bytes": "1.0.8",
+            "elm/html": "1.0.0",
+            "elm/virtual-dom": "1.0.3"
+        }
+    }
+}

exercises/practice/dnd-character/src/DndCharacter.elm

@@ -0,0 +1,29 @@
+module DndCharacter exposing (Character, ability, character, modifier)
+
+import Random exposing (Generator)
+
+
+type alias Character =
+    { strength : Int
+    , dexterity : Int
+    , constitution : Int
+    , intelligence : Int
+    , wisdom : Int
+    , charisma : Int
+    , hitpoints : Int
+    }
+
+
+modifier : Int -> Int
+modifier score =
+    Debug.todo "Please implement modifier"
+
+
+ability : Generator Int
+ability =
+    Debug.todo "Please implement ability"
+
+
+character : Generator Character
+character =
+    Debug.todo "Please implement character"