Code:

```
class KeyStore s where  [20:40]
  lookup :: s -> k -> Maybe v

instance KeyStore (Map.Map k v) where
  lookup store key = Map.lookup key store
```

Error:
```
test/KeyStoreSpec.hs:7:37: error:
    • Couldn't match type ‘k1’ with ‘k’
      Expected: Map k1 v1
        Actual: Map k v
      ‘k1’ is a rigid type variable bound by
        the type signature for:
          KeyStore.lookup :: forall k1 v1. Map k v -> k1 -> Maybe v1
        at test/KeyStoreSpec.hs:7:3-8
      ‘k’ is a rigid type variable bound by
        the instance declaration
        at test/KeyStoreSpec.hs:6:10-31
    • In the second argument of ‘Map.lookup’, namely ‘store’
      In the expression: Map.lookup key store
      In an equation for ‘KeyStore.lookup’:
          KeyStore.lookup store key = Map.lookup key store
    • Relevant bindings include
        key :: k1 (bound at test/KeyStoreSpec.hs:7:16)
        store :: Map k v (bound at test/KeyStoreSpec.hs:7:10)
        lookup :: Map k v -> k1 -> Maybe v1
          (bound at test/KeyStoreSpec.hs:7:3)
  |
7 |   lookup store key = Map.lookup key store
  |                                     ^^^^^
```