17 Jun
2014
17 Jun
'14
5:46 p.m.
Hi Nikolay,
On 16 June 2014 18:19, Nikolay Amiantov
If I disable OverloadedLists extension, warning goes away. Can someone clear this behaviour out for me? It looks like a bug, but I'm not sure.
I am not sure if this is a bug or not, but this page seems to explain the desugaring of patterns with OverloadedLists: https://ghc.haskell.org/trac/ghc/wiki/OverloadedLists As a workaround, you could try calling `toList` explicitly in a case statement to implement a `len` function for types with an IsList instance. Maybe something like the following. len :: IsList l => l -> Int len xs = case toList xs of [] -> ... Or even: len :: IsList l => l -> Int len = length . toList Hope this helps. -- Ozgur Akgun