From 1b56b31e809efb930a67ce6795323f0bbc0ab4ec Mon Sep 17 00:00:00 2001
From: Gary Verhaegen <gary.verhaegen@digitalasset.com>
Date: Thu, 25 Feb 2021 10:33:52 +0100
Subject: [PATCH] document potentially-surprising Month <-> Enum (#8923)

Based on a [forum question] by Alxander Bernauer.

[forum question]: https://discuss.daml.com/t/enum-instance-for-month-is-misleading/2098?u=gary_verhaegen

CHANGELOG_BEGIN
CHANGELOG_END
---
 compiler/damlc/daml-stdlib-src/DA/Date/Types.daml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/compiler/damlc/daml-stdlib-src/DA/Date/Types.daml b/compiler/damlc/daml-stdlib-src/DA/Date/Types.daml
index 8ebb8a9c55d..c8da10fd713 100644
--- a/compiler/damlc/daml-stdlib-src/DA/Date/Types.daml
+++ b/compiler/damlc/daml-stdlib-src/DA/Date/Types.daml
@@ -17,6 +17,9 @@ data DayOfWeek
     | Sunday
 
 -- | The `Month` type represents a month in the Gregorian calendar.
+--
+-- Note that, while `Month` has an `Enum` instance, the `toEnum` and `fromEnum`
+-- functions start counting at 0, i.e. `toEnum 1 :: Month` is `Feb`.
 data Month
     = Jan
     | Feb