From 3c29e7e92c67349ff65bc8905cc48b40ff9bce3f Mon Sep 17 00:00:00 2001
From: Bodigrim <andrew.lelechenko@gmail.com>
Date: Wed, 7 Jan 2026 22:39:43 +0000
Subject: [PATCH] Add another example for GHC-39999

---
 .../GHC-39999/overloaded-number/after/Lib.hs  |  4 +++
 .../GHC-39999/overloaded-number/before/Lib.hs |  4 +++
 .../GHC-39999/overloaded-number/index.md      | 31 +++++++++++++++++++
 3 files changed, 39 insertions(+)
 create mode 100644 message-index/messages/GHC-39999/overloaded-number/after/Lib.hs
 create mode 100644 message-index/messages/GHC-39999/overloaded-number/before/Lib.hs
 create mode 100644 message-index/messages/GHC-39999/overloaded-number/index.md

diff --git a/message-index/messages/GHC-39999/overloaded-number/after/Lib.hs b/message-index/messages/GHC-39999/overloaded-number/after/Lib.hs
new file mode 100644
index 00000000..4860b7b1
--- /dev/null
+++ b/message-index/messages/GHC-39999/overloaded-number/after/Lib.hs
@@ -0,0 +1,4 @@
+module Lib where
+
+foo :: [Int]
+foo = map (+ 1) [0]
diff --git a/message-index/messages/GHC-39999/overloaded-number/before/Lib.hs b/message-index/messages/GHC-39999/overloaded-number/before/Lib.hs
new file mode 100644
index 00000000..faae5bd3
--- /dev/null
+++ b/message-index/messages/GHC-39999/overloaded-number/before/Lib.hs
@@ -0,0 +1,4 @@
+module Lib where
+
+foo :: [Int]
+foo = map (+ 1) 0
diff --git a/message-index/messages/GHC-39999/overloaded-number/index.md b/message-index/messages/GHC-39999/overloaded-number/index.md
new file mode 100644
index 00000000..e72a2589
--- /dev/null
+++ b/message-index/messages/GHC-39999/overloaded-number/index.md
@@ -0,0 +1,31 @@
+---
+title: No instance for ‘Num [Int]’ arising from the literal ‘0’
+order: 5
+---
+
+## Error message
+
+```
+Lib.hs:4:17: error: [GHC-39999]
+    • No instance for ‘Num [Int]’ arising from the literal ‘0’
+    • In the second argument of ‘map’, namely ‘0’
+      In the expression: map (+ 1) 0
+      In an equation for ‘foo’: foo = map (+ 1) 0
+  |
+4 | foo = map (+ 1) 0
+  |                 ^
+```
+
+## Explanation
+
+Sometimes, when GHC encounters a type error, it suggests solving
+it from an unexpected end. In this case, when it encouters a literal
+instead of a list, it does not just complain about it. Instead it suspects
+that maybe an author meant to overload numeric literals so that they can mean lists too.
+
+Every time you write a numeric literal in Haskell,
+it gets desugared using `fromInteger :: Num a => Integer -> a`. So the program above
+would be absolutely valid if only `[Int]` itself (not just `Int`) was an instance of `Num`.
+While such interpretation of lists is not entirely out of the realm of possibility
+(say, imagine that lists represent coefficients of polynomials), it's much more likely
+that `map (+ 1) 0` is just a typo.