From a98a69f524f995559a24c2a0a5c31a5ed76d276e Mon Sep 17 00:00:00 2001
From: nicolas tabareau <nicolas.tabareau@inria.fr>
Date: Wed, 16 Dec 2020 21:54:33 +0100
Subject: [PATCH] experiment with cubical equality

---
 cubical-agda-test.agda | 48 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 cubical-agda-test.agda

diff --git a/cubical-agda-test.agda b/cubical-agda-test.agda
new file mode 100644
index 0000000..a7f077e
--- /dev/null
+++ b/cubical-agda-test.agda
@@ -0,0 +1,48 @@
+{-# OPTIONS --cubical #-}
+
+-- Definition of Identity types and definitions of J,
+-- funExt, univalence and propositional truncation
+-- using Id instead of Path
+
+open import Cubical.Foundations.Id public
+open import Cubical.Data.Bool public
+
+variable ℓ ℓ₁ ℓ₂ ℓ₃ ℓ₄ : Level
+
+etaBool : (a : Bool) → a ≡ (if a then true else false)
+etaBool true = refl
+etaBool false = refl
+
+test : (λ (b : Bool) → b) ≡ (λ (b : Bool) → if b then true else false)
+test = funExt (λ a → etaBool a)
+
+-- non-standard boolean using Id
+
+std-bool : Bool
+std-bool = transport (λ f → Bool) test true
+
+data eq {A : Type ℓ} (x : A) : A → Type ℓ where
+  eq-refl : eq x x 
+
+path-of-eq : {A : Type ℓ} {x y : A} → eq x y → Path A x y 
+path-of-eq {ℓ} {A} {x} {.x} eq-refl = reflPath
+
+eq-of-path : {A : Type ℓ} {x y : A} → Path A x y → eq x y
+eq-of-path {ℓ} {A} {x} {y} = JPath (λ y _ → eq x y) eq-refl
+
+etaBool' : (a : Bool) → eq a (if a then true else false)
+etaBool' true = eq-refl
+etaBool' false = eq-refl
+
+funext : {A : Set ℓ} {B : A → Set ℓ₁} {f g : (a : A) → B a} →
+          ((a : A) → eq (f a) (g a)) → eq f g 
+funext {ℓ} {ℓ₁} {A} {B} {f} {g} e = eq-of-path (funExtPath (λ (a : A) → path-of-eq (e a)))
+
+test' : eq (λ (b : Bool) → b) (λ (b : Bool) → if b then true else false)
+test' = funext (λ a → etaBool' a)
+
+transportEq : {A : Type ℓ} (P : A → Type ℓ₁) (x : A) (t : P x) (y : A) (e : eq x y) → P y
+transportEq P x t y eq-refl = t
+
+non-std-bool : Bool
+non-std-bool = transportEq (λ f → Bool) _ true _ test'