Hello Francesco,

> `Map k v` is already an instance of `Monoid` (when `v` is an instance of `Ord`), are you sure you need to write another one?

Thanks for your answer!

My "Values" is a Monoid, however it seems that the Graph cannot properly be seen correctly as a Monoid

using mconcat does not (properly) work, meaning that <> is not correctly applied to the someMonoids

so instead of

type G = Map Text someMonoid

mconcat [gs]

I have to write:

foldr (Map.unionWith (<>)) Map.empty [gs]

This passes the tests.

Same Problem with

g1 <> g2 --(Does not work properly)

and

Map.unionWith (<>) g1 g2 --(Does work)

I have declared someMonoid myself, do I need to declare something special about it?

I feel like my G is messing up with <> being about him, or about someMonoid

A broken down piece of code is:

import Data.Map as Map

data Sum = Sum Int deriving (Eq,Show)

instance Semigroup Sum where 
    (<>) (Sum a) (Sum b)= Sum(a + b) 
instance Monoid Sum where 
    mempty = Sum 0 

type G = Map.Map String Sum

And to verify my problem:

GHCI > v = Map.singleton "A" (Sum 1)

GHCI > u = Map.singleton "A" (Sum 1)

GHCI> c= v <> u

GHCI> Map.lookup "A" c

Just (Sum 1)

but I want

Just (Sum 2)

thanks

Leonhard