[Git][ghc/ghc][master] docs: fix ScopedTypeVariables example (#24101)

[Marge Bot (@marge-bot)]

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


Commits:
7a90020f by Krzysztof Gogolewski at 2023-10-31T20:03:37-04:00
docs: fix ScopedTypeVariables example (#24101)

The previous example didn't compile.

Furthermore, it wasn't demonstrating the point properly.
I have changed it to an example which shows that 'a' in the signature
must be the same 'a' as in the instance head.

- - - - -


1 changed file:

- docs/users_guide/exts/scoped_type_variables.rst


Changes:

=====================================
docs/users_guide/exts/scoped_type_variables.rst
=====================================
@@ -293,11 +293,11 @@ signatures/ of the methods. For example, the following will be accepted without
 explicitly enabling :extension:`ScopedTypeVariables`: ::
 
       class D a where
-        m :: [a] -> a
+        m :: a -> a
 
-      instance D [a] where
+      instance Num a => D [a] where
         m :: [a] -> [a]
-        m = reverse
+        m x = map (*2) x
 
 Note that writing ``m :: [a] -> [a]`` requires the use of the
 :extension:`InstanceSigs` extension.



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/7a90020f167ab016cbfa95decafaa1a54a974bc6

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/7a90020f167ab016cbfa95decafaa1a54a974bc6
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