From 7ceab6a725e5bd17c05bfd381753e453b15afaf7 Mon Sep 17 00:00:00 2001
From: Son Ho
Date: Mon, 3 Jul 2023 16:46:59 +0200
Subject: Add a missing case in the validity proofs

---
 backends/lean/Base/Diverge/Elab.lean | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

(limited to 'backends/lean')

diff --git a/backends/lean/Base/Diverge/Elab.lean b/backends/lean/Base/Diverge/Elab.lean
index cf40ea8f..063480a2 100644
--- a/backends/lean/Base/Diverge/Elab.lean
+++ b/backends/lean/Base/Diverge/Elab.lean
@@ -378,17 +378,22 @@ mutual
 partial def proveExprIsValid (k_var kk_var : Expr) (e : Expr) : MetaM Expr := do
   trace[Diverge.def.valid] "proveValid: {e}"
   match e with
+  | .const _ _ => throwError "Unimplemented" -- Shouldn't get there?
   | .bvar _
   | .fvar _
-  | .mvar _
-  | .sort _
   | .lit _
-  | .const _ _ => throwError "Unimplemented"
+  | .mvar _
+  | .sort _ => throwError "Unreachable"
   | .lam .. => throwError "Unimplemented"
   | .forallE .. => throwError "Unreachable" -- Shouldn't get there
-  | .letE .. => throwError "TODO"
-    -- lambdaLetTelescope e fun xs b => mapVisitBinders xs do
-    --  mkLambdaFVars xs (← mapVisit k b) (usedLetOnly := false)
+  | .letE dName dTy dValue body _nonDep => do
+    -- Introduce a local declaration for the let-binding
+    withLetDecl dName dTy dValue fun decl => do
+    let isValid ← proveExprIsValid k_var kk_var body
+    -- Add the let-binding around (rem.: the let-binding should be
+    -- *inside* the `is_valid_p`, not outside, but because it reduces
+    -- in the end it doesn't matter)
+    mkLetFVars #[decl] isValid
   | .mdata _ b => proveExprIsValid k_var kk_var b
   | .proj _ _ _ =>
     -- The projection shouldn't use the continuation
@@ -963,4 +968,12 @@ mutual
     if i > 20 then foo (i / 20) else .ret 42
 end
 
+-- Testing dependent branching and let-bindings
+-- TODO: why the linter warning?
+divergent def is_non_zero (i : Int) : Result Bool :=
+  if _h:i = 0 then return false
+  else
+    let b := true
+    return b
+
 end Diverge
-- 
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