Write the code and the tests

exercises/concept/role-playing-game/elm.json

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+{
+    "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": "1.2.2",
+            "rtfeldman/elm-iso8601-date-strings": "1.1.3"
+        },
+        "indirect": {
+            "elm/html": "1.0.0",
+            "elm/virtual-dom": "1.0.2"
+        }
+    }
+}

exercises/concept/role-playing-game/src/RolePlayingGame.elm

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+module RolePlayingGame exposing (Player, castSpell, revive)
+
+
+type alias Player =
+    { level : Int
+    , health : Int
+    , mana : Maybe Int
+    }
+
+
+revive : Player -> Maybe Player
+revive player =
+    if player.health > 0 then
+        Nothing
+
+    else if player.level >= 10 then
+        Just { player | health = 100, mana = Just 100 }
+
+    else
+        Just { player | health = 100, mana = Nothing }
+
+
+castSpell : Int -> Player -> ( Player, Int )
+castSpell manaCost player =
+    case player.mana of
+        Nothing ->
+            ( { player | health = max 0 (player.health - manaCost) }, 0 )
+
+        Just mana ->
+            if mana >= manaCost then
+                ( { player | mana = Just (mana - manaCost) }, 2 * manaCost )
+
+            else
+                ( player, 0 )

exercises/concept/role-playing-game/tests/Tests.elm

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+module Tests exposing (tests)
+
+import Expect
+import RolePlayingGame exposing (Player, castSpell, revive)
+import Test exposing (..)
+
+
+tests : Test
+tests =
+    describe "RolePlayingGame"
+        [ test "Attempting to revive a player that is alive should return Nothing" <|
+            \() -> Expect.equal (revive { level = 12, health = 42, mana = Just 7 }) Nothing
+        , test "Reviving a low level player resets its health to 100" <|
+            \() ->
+                Expect.equal (revive { level = 3, health = 0, mana = Nothing })
+                    (Just { level = 3, health = 100, mana = Nothing })
+        , test "Reviving a high level player resets both its health and mana" <|
+            \() ->
+                Expect.equal (revive { level = 10, health = 0, mana = Just 14 })
+                    (Just { level = 10, health = 100, mana = Just 100 })
+        , test "Casting a spell spends double the mana" <|
+            \() ->
+                Expect.equal (castSpell 9 { level = 10, health = 69, mana = Just 20 })
+                    ( { level = 10, health = 69, mana = Just 11 }, 18 )
+        , test "Attempting to cast a spell with insufficient mana does nothing" <|
+            \() ->
+                Expect.equal (castSpell 39 { level = 10, health = 69, mana = Just 20 })
+                    ( { level = 10, health = 69, mana = Just 20 }, 0 )
+        , test "Attempting to cast a spell without a mana pool decreases the player's health" <|
+            \() ->
+                Expect.equal (castSpell 7 { level = 5, health = 58, mana = Nothing })
+                    ( { level = 5, health = 51, mana = Nothing }, 0 )
+        , test "A player's health cannot go below 0" <|
+            \() ->
+                Expect.equal (castSpell 12 { level = 5, health = 6, mana = Nothing })
+                    ( { level = 5, health = 0, mana = Nothing }, 0 )
+        ]