Use instances to simplify printing code

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

Lattice/FiniteMap.agda

@@ -45,11 +45,17 @@ open import Function using (_∘_)
 open import Relation.Nullary using (¬_; Dec; yes; no)
 open import Utils using (Pairwise; _∷_; [])
 open import Data.Empty using (⊥-elim)
+open import Showable using (Showable; show)
 
 module WithKeys (ks : List A) where
     FiniteMap : Set (a ⊔ℓ b)
     FiniteMap = Σ Map (λ m → Map.keys m ≡ ks)
 
+    instance
+        showable : {{ showableA : Showable A }} {{ showableB : Showable B }} →
+                   Showable FiniteMap
+        showable = record { show = λ (m₁ , _) → show m₁ }
+
     _≈_ : FiniteMap → FiniteMap → Set (a ⊔ℓ b)
     _≈_ (m₁ , _) (m₂ , _) = m₁ ≈ᵐ m₂