Simplify Context extension (#809)

* Simplify Context extension

* nit: s/`fmap`/<$>/

Author: layus

src/Nix/Context.hs

@@ -20,16 +20,16 @@ data Context m t = Context
     }
 
 instance Has (Context m t) (Scopes m t) where
-  hasLens f (Context x y z w) = (\x' -> Context x' y z w) <$> f x
+  hasLens f a = (\x -> a { scopes = x }) <$> f (scopes a)
 
 instance Has (Context m t) SrcSpan where
-  hasLens f (Context x y z w) = (\y' -> Context x y' z w) <$> f y
+  hasLens f a = (\x -> a { source = x }) <$> f (source a)
 
 instance Has (Context m t) Frames where
-  hasLens f (Context x y z w) = (\z' -> Context x y z' w) <$> f z
+  hasLens f a = (\x -> a { frames = x }) <$> f (frames a)
 
 instance Has (Context m t) Options where
-  hasLens f (Context x y z w) = (\w' -> Context x y z w') <$> f w
+  hasLens f a = (\x -> a { options = x }) <$> f (options a)
 
 newContext :: Options -> Context m t
 newContext = Context emptyScopes nullSpan []

src/Nix/Options.hs

@@ -9,7 +9,7 @@ data Options = Options
     , tracing      :: Bool
     , thunks       :: Bool
     , values       :: Bool
-    , scopes       :: Bool
+    , showScopes   :: Bool
     , reduce       :: Maybe FilePath
     , reduceSets   :: Bool
     , reduceLists  :: Bool
@@ -42,7 +42,7 @@ defaultOptions current = Options { verbose      = ErrorsOnly
                                  , tracing      = False
                                  , thunks       = False
                                  , values       = False
-                                 , scopes       = False
+                                 , showScopes   = False
                                  , reduce       = Nothing
                                  , reduceSets   = False
                                  , reduceLists  = False

src/Nix/Render/Frame.hs

@@ -106,7 +106,7 @@ renderEvalFrame level f = do
   opts :: Options <- asks (view hasLens)
   case f of
     EvaluatingExpr scope e@(Fix (Compose (Ann ann _))) -> do
-      let scopeInfo | scopes opts = [pretty $ show scope]
+      let scopeInfo | showScopes opts = [pretty $ show scope]
                     | otherwise   = []
       fmap (\x -> scopeInfo ++ [x])
         $   renderLocation ann