Use instances to simplify printing code

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

Lattice/AboveBelow.agda

@@ -11,6 +11,7 @@ open import Data.Empty using (⊥-elim)
 open import Data.Product using (_,_)
 open import Data.Nat using (_≤_; ℕ; z≤n; s≤s; suc)
 open import Function using (_∘_)
+open import Showable using (Showable; show)
 open import Relation.Binary.PropositionalEquality as Eq
     using (_≡_; sym; subst; refl)
 
@@ -24,6 +25,16 @@ data AboveBelow : Set a where
     ⊤ : AboveBelow
     [_] : A → AboveBelow
 
+instance
+    showable : {{ showableA : Showable A }} → Showable AboveBelow
+    showable = record
+        { show = (λ
+            { ⊥ → "⊥"
+            ; ⊤ → "⊤"
+            ; [ a ] → show a
+            })
+        }
+
 data _≈_ : AboveBelow → AboveBelow → Set a where
     ≈-⊥-⊥ : ⊥ ≈ ⊥
     ≈-⊤-⊤ : ⊤ ≈ ⊤