[Git][ghc/ghc][master] Fix example in GHC user guide in SafeHaskell section

[Marge Bot (@marge-bot)]

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC


Commits:
5a2fe35a by David Binder at 2023-09-05T00:39:07-04:00
Fix example in GHC user guide in SafeHaskell section

The example given in the SafeHaskell section uses an implementation of
Monad which no longer works. This MR removes the non-canonical return
instance and adds the necessary instances of Functor and Applicative.

- - - - -


1 changed file:

- docs/users_guide/exts/safe_haskell.rst


Changes:

=====================================
docs/users_guide/exts/safe_haskell.rst
=====================================
@@ -109,8 +109,14 @@ define the plugin interface so that it requires the plugin module,
     -- Notice that symbol UnsafeRIO is not exported from this module!
     newtype RIO a = UnsafeRIO { runRIO :: IO a }
 
+    instance Functor RIO where
+        fmap f (UnsafeRIO m) = UnsafeRIO (fmap f m)
+
+    instance Applicative RIO where
+        pure = UnsafeRIO . pure
+        (UnsafeRIO f) <*> (UnsafeRIO m) = UnsafeRIO (f <*> m)
+
     instance Monad RIO where
-        return = UnsafeRIO . return
         (UnsafeRIO m) >>= k = UnsafeRIO $ m >>= runRIO . k
 
     -- Returns True iff access is allowed to file name



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5a2fe35a84cbcedc929f313e34c45d6f02d81607

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5a2fe35a84cbcedc929f313e34c45d6f02d81607
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