Merge pull request #1540 from MatthijsBlom/correct-functor-law-hint

Correct Functor law hint
ndmitchell · Jan 14, 2024 · a7df70f · a7df70f
2 parents 551fe9a + a30f516
commit a7df70f
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Showing 2 changed files with 19 additions and 2 deletions.
diff --git a/data/hlint.yaml b/data/hlint.yaml
@@ -472,11 +472,12 @@
     # FUNCTOR
 
     - warn: {lhs: fmap f (fmap g x), rhs: fmap (f . g) x, name: Functor law}
-    - warn: {lhs: f <$> g <$> x, rhs: f . g <$> x, name: Functor law}
+    - warn: {lhs: f <$> (g <$> x), rhs: f . g <$> x, name: Functor law}
     - warn: {lhs: x <&> g <&> f, rhs: x <&> f . g, name: Functor law}
     - warn: {lhs: fmap id, rhs: id, name: Functor law}
     - warn: {lhs: id <$> x, rhs: x, name: Functor law}
     - warn: {lhs: x <&> id, rhs: x, name: Functor law}
+    - warn: {lhs: f <$> g <$> x, rhs: f . g <$> x}
     - hint: {lhs: fmap f $ x, rhs: f <$> x, side: isApp x || isAtom x}
     - hint: {lhs: \x -> a <$> b x, rhs: fmap a . b}
     - hint: {lhs: \x -> b x <&> a, rhs: fmap a . b}

diff --git a/hints.md b/hints.md
@@ -7199,7 +7199,7 @@ fmap (f . g) x
 <td>
 LHS:
 <code>
-f <$> g <$> x
+f <$> (g <$> x)
 </code>
 <br>
 RHS:
@@ -7275,6 +7275,22 @@ x
 <td>Warning</td>
 </tr>
 <tr>
+<td>Redundant <$></td>
+<td>
+LHS:
+<code>
+f <$> g <$> x
+</code>
+<br>
+RHS:
+<code>
+f . g <$> x
+</code>
+<br>
+</td>
+<td>Warning</td>
+</tr>
+<tr>
 <td>Use <$></td>
 <td>
 LHS: