From 52dc88aa51ad690b8fa9c28c3737563f4acc01f3 Mon Sep 17 00:00:00 2001
From: Florian Engel <engelflorian@posteo.de>
Date: Sun, 13 Oct 2024 10:00:08 +0200
Subject: [PATCH] Document GHC-08838

---
 .../GHC-08838/WrongDoBind/after/WrongDoBind.hs   |  4 ++++
 .../GHC-08838/WrongDoBind/before/WrongDoBind.hs  |  6 ++++++
 .../messages/GHC-08838/WrongDoBind/index.md      | 16 ++++++++++++++++
 message-index/messages/GHC-08838/index.md        |  9 +++++++++
 4 files changed, 35 insertions(+)
 create mode 100644 message-index/messages/GHC-08838/WrongDoBind/after/WrongDoBind.hs
 create mode 100644 message-index/messages/GHC-08838/WrongDoBind/before/WrongDoBind.hs
 create mode 100644 message-index/messages/GHC-08838/WrongDoBind/index.md
 create mode 100644 message-index/messages/GHC-08838/index.md

diff --git a/message-index/messages/GHC-08838/WrongDoBind/after/WrongDoBind.hs b/message-index/messages/GHC-08838/WrongDoBind/after/WrongDoBind.hs
new file mode 100644
index 0000000..b6d93bb
--- /dev/null
+++ b/message-index/messages/GHC-08838/WrongDoBind/after/WrongDoBind.hs
@@ -0,0 +1,4 @@
+module WrongDoBind where
+
+doubleReturn :: forall m. Monad m => m Int
+doubleReturn = return 10
diff --git a/message-index/messages/GHC-08838/WrongDoBind/before/WrongDoBind.hs b/message-index/messages/GHC-08838/WrongDoBind/before/WrongDoBind.hs
new file mode 100644
index 0000000..1b76679
--- /dev/null
+++ b/message-index/messages/GHC-08838/WrongDoBind/before/WrongDoBind.hs
@@ -0,0 +1,6 @@
+module WrongDoBind where
+
+doubleReturn :: forall m. Monad m => m Int
+doubleReturn = do
+  return (return 10 :: m Int)
+  return 10
diff --git a/message-index/messages/GHC-08838/WrongDoBind/index.md b/message-index/messages/GHC-08838/WrongDoBind/index.md
new file mode 100644
index 0000000..234ed61
--- /dev/null
+++ b/message-index/messages/GHC-08838/WrongDoBind/index.md
@@ -0,0 +1,16 @@
+
+---
+title: Double return
+---
+
+In this example, there is a nested return whose result is not bound to a variable. Therefore the computation `return 10` is not used and can be removed.
+
+```
+messages/GHC-08838/WrongDoBind/before/WrongDoBind.hs:5:4: warning: [GHC-08838] [-Wwrong-do-bind]
+    A do-notation statement discarded a result of type ‘m Int’
+    Suggested fix:
+      Suppress this warning by saying ‘_ <- return (return 10 :: m Int)’
+  |
+5 |    return (return 10 :: m Int)
+  |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+```
diff --git a/message-index/messages/GHC-08838/index.md b/message-index/messages/GHC-08838/index.md
new file mode 100644
index 0000000..1aaa457
--- /dev/null
+++ b/message-index/messages/GHC-08838/index.md
@@ -0,0 +1,9 @@
+---
+title: Wrong do bind
+summary: Returning a monadic computation in a do block and not binding it will not run it
+severity: warning
+introduced: 9.4.1
+---
+When using a monadic computation in a do block one should either run it 
+directly or bind the result of the computation to a variable. If neither 
+is done the monadic computation is never run and can be removed.