Remove View (#439)

ChangeLog.md

@@ -4,6 +4,7 @@
 
 ### Breaking Changes
 
+- Removed `Polysemy.View`
 - Removed `Polysemy.Law`
 
 ### Other Changes

polysemy.cabal

@@ -76,7 +76,6 @@ library
       Polysemy.State
       Polysemy.Tagged
       Polysemy.Trace
-      Polysemy.View
       Polysemy.Writer
   other-modules:
       Polysemy.Internal.PluginLookup
@@ -147,7 +146,6 @@ test-suite polysemy-test
       TacticsSpec
       ThEffectSpec
       TypeErrors
-      ViewSpec
       WriterSpec
       Paths_polysemy
       Build_doctests

src/Polysemy/View.hs

@@ -1,76 +0,0 @@
-{-# LANGUAGE TemplateHaskell #-}
-
-module Polysemy.View
-  ( -- * Effect
-    View (..)
-
-    -- * Actions
-  , see
-
-    -- * Interpretations
-  , viewToState
-  , viewToInput
-  ) where
-
-import Polysemy
-import Polysemy.Input
-import Polysemy.State
-import Polysemy.Tagged
-
-
-------------------------------------------------------------------------------
--- | A 'View' is an expensive computation that should be cached.
-data View v m a where
-  See :: View v m v
-
-makeSem ''View
-
-
-------------------------------------------------------------------------------
--- | Transform a 'View' into an 'Input'.
-viewToInput
-    :: forall v i r a
-     . Member (Input i) r
-    => (i -> v)
-    -> Sem (View v ': r) a
-    -> Sem r a
-viewToInput f = interpret $ \case
-  See -> f <$> input
-
-
-------------------------------------------------------------------------------
--- | Get a 'View' as an exensive computation over an underlying 'State' effect.
--- This 'View' is only invalidated when the underlying 'State' changes.
-viewToState
-    :: forall v s r a
-     . Member (State s) r
-    => (s -> Sem r v)
-    -> Sem (View v ': r) a
-    -> Sem r a
-viewToState f = do
-  evalState Dirty
-    . untag @"view" @(State (Cached v))
-    . intercept @(State s)
-      ( \case
-        Get -> get
-        Put s -> do
-          put s
-          tag @"view" @(State (Cached v)) $ put $ Dirty @v
-      )
-    . reinterpret @(View v)
-      ( \case
-          See -> do
-            dirty <- tagged @"view" $ get @(Cached v)
-            case dirty of
-              Dirty -> do
-                s <- get
-                v' <- raise $ f s
-                tagged @"view" $ put $ Cached v'
-                pure v'
-              Cached v -> pure v
-      )
-
-
-data Cached a = Cached a | Dirty
-  deriving (Eq, Ord, Show, Functor)
-

test/ViewSpec.hs

@@ -1,40 +0,0 @@
-module ViewSpec where
-
-import Polysemy
-import Polysemy.State
-import Polysemy.Trace
-import Polysemy.View
-import Test.Hspec
-
-
-check_see :: Members '[View String, Trace] r => Sem r ()
-check_see = trace . ("saw " ++) =<< see
-
-spec :: Spec
-spec = parallel $ do
-  describe "View effect" $ do
-    it "should cache views" $ do
-      let a = run
-            . runTraceList
-            . runState @Int 0
-            . viewToState @String @Int (\i -> do
-                  trace $ "caching "  ++ show i
-                  pure $ show i  ) $ do
-              check_see
-              check_see
-              put @Int 3
-              trace "it's lazy"
-              put @Int 5
-              check_see
-              check_see
-              get @Int
-
-      a `shouldBe` ([ "caching 0"
-                    , "saw 0"
-                    , "saw 0"
-                    , "it's lazy"
-                    , "caching 5"
-                    , "saw 5"
-                    , "saw 5"
-                    ], (5, 5))
-