Add entities, and allow walking around

Add support for entities via a port of the EntityMap type, and implement
command support starting at basic hjkl.

src/Xanthous/Data.hs

@@ -0,0 +1,118 @@
+{-# LANGUAGE DeriveTraversable #-}
+{-# LANGUAGE DeriveFoldable #-}
+{-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE TemplateHaskell #-}
+--------------------------------------------------------------------------------
+-- | Common data types for Xanthous
+--------------------------------------------------------------------------------
+module Xanthous.Data
+  ( Position(..)
+  , x
+  , y
+
+  , Positioned(..)
+  , position
+  , positioned
+  , loc
+
+    -- *
+  , Direction(..)
+  , opposite
+  , move
+  , asPosition
+  ) where
+--------------------------------------------------------------------------------
+import Xanthous.Prelude hiding (Left, Down, Right)
+import Test.QuickCheck (Arbitrary, CoArbitrary, Function)
+import Test.QuickCheck.Arbitrary.Generic
+import Data.Group
+import Brick (Location(Location))
+--------------------------------------------------------------------------------
+import Xanthous.Util (EqEqProp(..), EqProp)
+--------------------------------------------------------------------------------
+
+data Position where
+  Position :: { _x :: Int
+             , _y :: Int
+             } -> Position
+  deriving stock (Show, Eq, Generic, Ord)
+  deriving anyclass (Hashable, CoArbitrary, Function)
+  deriving EqProp via EqEqProp Position
+makeLenses ''Position
+
+instance Arbitrary Position where
+  arbitrary = genericArbitrary
+  shrink = genericShrink
+
+instance Semigroup Position where
+  (Position x₁ y₁) <> (Position x₂ y₂) = Position (x₁ + x₂) (y₁ + y₂)
+
+instance Monoid Position where
+  mempty = Position 0 0
+
+instance Group Position where
+  invert (Position px py) = Position (-px) (-py)
+
+data Positioned a where
+  Positioned :: Position -> a -> Positioned a
+  deriving stock (Show, Eq, Ord, Functor, Foldable, Traversable, Generic)
+  deriving anyclass (CoArbitrary, Function)
+
+instance Arbitrary a => Arbitrary (Positioned a) where
+  arbitrary = Positioned <$> arbitrary <*> arbitrary
+
+position :: Lens' (Positioned a) Position
+position = lens
+  (\(Positioned pos _) -> pos)
+  (\(Positioned _ a) pos -> Positioned pos a)
+
+positioned :: Lens (Positioned a) (Positioned b) a b
+positioned = lens
+  (\(Positioned _ x') -> x')
+  (\(Positioned pos _) x' -> Positioned pos x')
+
+loc :: Iso' Position Location
+loc = iso hither yon
+  where
+    hither (Position px py) = Location (px, py)
+    yon (Location (lx, ly)) = Position lx ly
+
+--------------------------------------------------------------------------------
+
+data Direction where
+  Up        :: Direction
+  Down      :: Direction
+  Left      :: Direction
+  Right     :: Direction
+  UpLeft    :: Direction
+  UpRight   :: Direction
+  DownLeft  :: Direction
+  DownRight :: Direction
+  deriving stock (Show, Eq, Generic)
+
+instance Arbitrary Direction where
+  arbitrary = genericArbitrary
+  shrink = genericShrink
+
+opposite :: Direction -> Direction
+opposite Up        = Down
+opposite Down      = Up
+opposite Left      = Right
+opposite Right     = Left
+opposite UpLeft    = DownRight
+opposite UpRight   = DownLeft
+opposite DownLeft  = UpRight
+opposite DownRight = UpLeft
+
+move :: Direction -> Position -> Position
+move Up        = y -~ 1
+move Down      = y +~ 1
+move Left      = x -~ 1
+move Right     = x +~ 1
+move UpLeft    = move Up . move Left
+move UpRight   = move Up . move Right
+move DownLeft  = move Down . move Left
+move DownRight = move Down . move Right
+
+asPosition :: Direction -> Position
+asPosition dir = move dir mempty