From 1018aa1af83e639a6b41b5650bf3b717e7f8de68 Mon Sep 17 00:00:00 2001
From: Son Ho
Date: Wed, 12 Jun 2024 14:46:52 +0200
Subject: Deactivate the coercion from Nat to Scalar

---
 backends/lean/Base/Arith/Scalar.lean      | 10 ++++++++++
 backends/lean/Base/Primitives/Scalar.lean |  7 +++++++
 2 files changed, 17 insertions(+)

(limited to 'backends/lean')

diff --git a/backends/lean/Base/Arith/Scalar.lean b/backends/lean/Base/Arith/Scalar.lean
index c2e4e24e..8793713b 100644
--- a/backends/lean/Base/Arith/Scalar.lean
+++ b/backends/lean/Base/Arith/Scalar.lean
@@ -80,4 +80,14 @@ example (x : Int) (h0 : 0 ≤ x) (h1 : x ≤ U32.max) :
 example (x : U32) (h0 : ¬ x = U32.ofInt 0) : 0 < x.val := by
   scalar_tac
 
+/- See this: https://aeneas-verif.zulipchat.com/#narrow/stream/349819-general/topic/U64.20trouble/near/444049757
+
+   We solved it by removing the instance `OfNat` for `Scalar`.
+   Note however that we could also solve it with a simplification lemma.
+   However, after testing, we noticed we could only apply such a lemma with
+   the rewriting tactic (not the simplifier), probably because of the use
+   of typeclasses. -/
+example {u: U64} (h1: (u : Int) < 2): (u : Int) = 0 ∨ (u : Int) = 1 := by
+  scalar_tac
+
 end Arith
diff --git a/backends/lean/Base/Primitives/Scalar.lean b/backends/lean/Base/Primitives/Scalar.lean
index 8fb067e1..157ade2c 100644
--- a/backends/lean/Base/Primitives/Scalar.lean
+++ b/backends/lean/Base/Primitives/Scalar.lean
@@ -351,10 +351,17 @@ instance [Decide (Scalar.cMin ty ≤ v ∧ v ≤ Scalar.cMax ty)] : InBounds ty
 @[simp] abbrev Scalar.check_bounds (ty : ScalarTy) (x : Int) : Bool :=
   (Scalar.cMin ty ≤ x || Scalar.min ty ≤ x) ∧ (x ≤ Scalar.cMax ty || x ≤ Scalar.max ty)
 
+/- Discussion:
+   This coercion can be slightly annoying at times, because if we write
+   something like `u = 3` (where `u` is, for instance, as `U32`), then instead of
+   coercing `u` to `Int`, Lean will lift `3` to `U32`).
+   For now we deactivate it.
+
 -- TODO(raitobezarius): the inbounds constraint is a bit ugly as we can pretty trivially
 -- discharge the lhs on ≥ 0.
 instance {ty: ScalarTy} [InBounds ty (Int.ofNat n)]: OfNat (Scalar ty) (n: ℕ) where
   ofNat := Scalar.ofInt n
+-/
 
 theorem Scalar.check_bounds_imp_in_bounds {ty : ScalarTy} {x : Int}
   (h: Scalar.check_bounds ty x) :
-- 
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