From fd35bac4b2d67d2639cf9249b1f187a523d06151 Mon Sep 17 00:00:00 2001
From: Alexey Kiryushin <alexey.a.kiryushin@gmail.com>
Date: Thu, 16 Jan 2020 21:35:01 +0300
Subject: [PATCH] Add a suggestion to use the 'force' function in the
 'uninitialised element' error message (#231)

Compaction of an immutable vector may crash with the confusing 'uninitialised element' error message (#220). The workaround is to use the 'force' function.
---
 Data/Vector/Mutable.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Data/Vector/Mutable.hs b/Data/Vector/Mutable.hs
index f346bc0..8891889 100644
--- a/Data/Vector/Mutable.hs
+++ b/Data/Vector/Mutable.hs
@@ -193,7 +193,7 @@ loopM !n k = let
   in go 0
 
 uninitialised :: a
-uninitialised = error "Data.Vector.Mutable: uninitialised element"
+uninitialised = error "Data.Vector.Mutable: uninitialised element. If you are trying to compact a vector, use the 'force' function to remove uninitialised elements from the underlying array."
 
 -- Length information
 -- ------------------
-- 
GitLab