Add lenses.hs

lenses.hs

@@ -0,0 +1,71 @@
+
+{-
+
+here i show how to use lenses to handle states (didnt found any example on states in internet)
+
+-}
+
+
+{-# LANGUAGE TemplateHaskell #-}
+import Lens.Micro.TH (makeLenses)
+import Lens.Micro ((%~), (.~), (&), _2)
+import Lens.Micro.Platform (at)  -- Correct import for Map operations
+import Data.IORef (IORef, newIORef, modifyIORef', readIORef)
+import Data.Map (Map)
+import qualified Data.Map as Map
+
+
+data AppState = AppState
+  { _ui :: UIState
+  , _user :: User
+  } deriving (Show)  
+
+data UIState = UIState
+  { _theme :: String
+  , _windowSize :: (Int, Int)
+  , _keyBindings :: Map String String
+  } deriving (Show)  
+
+data User = User
+  { _name :: String
+  , _prefs :: UserPrefs
+  } deriving (Show) 
+
+data UserPrefs = UserPrefs
+  { _fontSize :: Int
+  , _darkMode :: Bool
+  } deriving (Show) 
+
+
+makeLenses ''AppState
+makeLenses ''UIState
+makeLenses ''User
+makeLenses ''UserPrefs
+
+main :: IO ()
+main = do
+  let initialState = AppState
+        { _ui = UIState
+          { _theme = "light"
+          , _windowSize = (800, 600)
+          , _keyBindings = Map.fromList [("Ctrl+S", "save")]
+          }
+        , _user = User
+          { _name = "Alice"
+          , _prefs = UserPrefs
+            { _fontSize = 12
+            , _darkMode = False
+            }
+          }
+        }
+
+  stateRef <- newIORef initialState
+
+  -- Corrected lens chain with &
+  modifyIORef' stateRef $ \s ->
+    s & ui . keyBindings . at "Ctrl+X" .~ Just "cut"
+      & user . prefs . darkMode .~ True
+      & ui . windowSize . _2 %~ (+100)
+
+  finalState <- readIORef stateRef
+  print finalState