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{-# LANGUAGE TypeFamilies #-}
-- Trac #3017
module Foo where
class Coll c where
type Elem c
empty :: c
insert :: Elem c -> c -> c
data ListColl a = L [a]
instance Coll (ListColl a) where
type Elem (ListColl a) = a
empty = L []
insert x (L xs) = L (x:xs)
emptyL :: ListColl a
emptyL = empty
test2 c = insert (0, 0) c
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