Merge pull request #447 from haskellfoundation/GHC-64088

Add message for GHC-64088 : Use of forall identifier

Author: BinderDavid

message-index/messages/GHC-64088/forall-identifier/after/ForallIdentifier.hs

@@ -0,0 +1,4 @@
+module ForallIdentifier where
+
+forAll :: (a -> Bool) -> [a] -> Bool
+forAll f ls = and (fmap f ls)

message-index/messages/GHC-64088/forall-identifier/before/ForallIdentifier.hs

@@ -0,0 +1,4 @@
+module ForallIdentifier where
+
+forall :: (a -> Bool) -> [a] -> Bool
+forall f ls = and (map f ls)

message-index/messages/GHC-64088/forall-identifier/index.md

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+---
+title: The identifier "forall" should not be used
+---
+
+In this example the programmer implemented a function which checks whether all elements of a list satisfy a given predicate. The programmer has chosen the sensible name "forall" for this function, but this name will become a reserved keyword in a future version of GHC.
+The function should therefore be renamed, for example to the name "forAll".
+
+```
+ForallIdentifier.hs:4:1: warning: [GHC-64088] [-Wforall-identifier]
+    The use of ‘forall’ as an identifier
+    will become an error in a future GHC release.
+    Suggested fix:
+      Consider using another name, such as
+      ‘forAll’, ‘for_all’, or ‘forall_’.
+  |
+4 | forall f ls = and (fmap f ls)
+  | ^^^^^^
+```

message-index/messages/GHC-64088/index.md

@@ -0,0 +1,11 @@
+---
+title: Use of "forall" as an identifier
+summary: Use of "forall" as an identifier is discouraged
+severity: warning
+flag: -Wforall-identifier
+introduced: 9.6.1
+---
+
+The string "forall" is not a keyword in the Haskell 2010 standard.
+It is therefore possible to declare a top-level function in Haskell 2010 which uses `forall` as a name.
+As a result of the accepted [GHC proposal 281](https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0281-visible-forall.rst) the string `"forall"` will become a reserved keyword in a future version of GHC, so GHC warns against the use of `forall` as an identifier.