Hi, I’m looking at a blog post on Monoids and finger trees at http://apfelmus.nfshost.com/articles/monoid-fingertree.html http://apfelmus.nfshost.com/articles/monoid-fingertree.html and would appreciate a bit of advice I have type Size = Int type Priority = Int instance Monoid Size where mempty = 0 mappend = (+) instance Monoid Priority where mempty = maxBound mappend = min and I get compiler error Duplicate instance declarations: instance Monoid Size -- Defined at /Users/mike/haskell/FingerTrees/Ftree.hs:60:10 instance Monoid Priority -- Defined at /Users/mike/haskell/FingerTrees/Ftree.hs:64:10 Which I can sort of understand as Size and Priority are both Int but on the other hand, internally, the monoids are different. Is this genuinely incorrect code or is there a language extension to get around this? Thanks Mike