Implement a map-reduce visitor for expressions and fix issues with ge…

…t{M,F}VarIds

backends/lean/Base/Utils.lean

@@ -159,47 +159,96 @@ elab "print_ctx_decls" : tactic => do
   let decls ← ctx.getDecls
   printDecls decls
 
--- A map visitor function for expressions (adapted from `AbstractNestedProofs.visit`)
+-- A map-reduce visitor function for expressions (adapted from `AbstractNestedProofs.visit`)
 -- The continuation takes as parameters:
 -- - the current depth of the expression (useful for printing/debugging)
 -- - the expression to explore
-partial def mapVisit (k : Nat → Expr → MetaM Expr) (e : Expr) : MetaM Expr := do
-  let mapVisitBinders (xs : Array Expr) (k2 : MetaM Expr) : MetaM Expr := do
+partial def mapreduceVisit {a : Type} (k : Nat → a → Expr → MetaM (a × Expr))
+  (state : a) (e : Expr) : MetaM (a × Expr) := do
+  let mapreduceVisitBinders (state : a) (xs : Array Expr) (k2 : a → MetaM (a × Expr)) :
+    MetaM (a × Expr) := do
     let localInstances ← getLocalInstances
-    let mut lctx ← getLCtx
-    for x in xs do
-      let xFVarId := x.fvarId!
-      let localDecl ← xFVarId.getDecl
-      let type      ← mapVisit k localDecl.type
-      let localDecl := localDecl.setType type
-      let localDecl ← match localDecl.value? with
-         | some value => let value ← mapVisit k value; pure <| localDecl.setValue value
-         | none       => pure localDecl
-      lctx :=lctx.modifyLocalDecl xFVarId fun _ => localDecl
-    withLCtx lctx localInstances k2
+    -- Update the local declarations for the bindings in context `lctx`
+    let rec visit_xs (lctx : LocalContext) (state : a) (xs : List Expr) : MetaM (LocalContext × a) := do
+      match xs with
+      | [] => pure (lctx, state)
+      | x :: xs => do
+        let xFVarId := x.fvarId!
+        let localDecl ← xFVarId.getDecl
+        let (state, type) ← mapreduceVisit k state localDecl.type
+        let localDecl := localDecl.setType type
+        let (state, localDecl) ← match localDecl.value? with
+           | some value =>
+             let (state, value) ← mapreduceVisit k state value
+             pure (state, localDecl.setValue value)
+           | none => pure (state, localDecl)
+        let lctx := lctx.modifyLocalDecl xFVarId fun _ => localDecl
+        -- Recursive call
+        visit_xs lctx state xs
+    let (lctx, state) ← visit_xs (← getLCtx) state xs.toList
+    -- Call the continuation with the updated context
+    withLCtx lctx localInstances (k2 state)
   -- TODO: use a cache? (Lean.checkCache)
-  let rec visit (i : Nat) (e : Expr) : MetaM Expr := do
+  let rec visit (i : Nat) (state : a) (e : Expr) : MetaM (a × Expr) := do
     -- Explore
-    let e ← k i e
+    let (state, e) ← k i state e
     match e with
     | .bvar _
     | .fvar _
     | .mvar _
     | .sort _
     | .lit _
-    | .const _ _ => pure e
-    | .app .. => do e.withApp fun f args => return mkAppN f (← args.mapM (visit (i + 1)))
+    | .const _ _ => pure (state, e)
+    | .app .. => do e.withApp fun f args => do
+      let (state, args) ← args.foldlM (fun (state, args) arg => do let (state, arg) ← visit (i + 1) state arg; pure (state, arg :: args)) (state, [])
+      let args := args.reverse
+      let (state, f) ← visit (i + 1) state f
+      let e' := mkAppN f (Array.mk args)
+      return (state, e')
     | .lam .. =>
       lambdaLetTelescope e fun xs b =>
-        mapVisitBinders xs do mkLambdaFVars xs (← visit (i + 1) b) (usedLetOnly := false)
+        mapreduceVisitBinders state xs fun state => do
+        let (state, b) ← visit (i + 1) state b
+        let e' ← mkLambdaFVars xs b (usedLetOnly := false)
+        return (state, e')
     | .forallE .. => do
-      forallTelescope e fun xs b => mapVisitBinders xs do mkForallFVars xs (← visit (i + 1) b)
+      forallTelescope e fun xs b =>
+         mapreduceVisitBinders state xs fun state => do
+         let (state, b) ← visit (i + 1) state b
+         let e' ← mkForallFVars xs b
+         return (state, e')
     | .letE .. => do
-      lambdaLetTelescope e fun xs b => mapVisitBinders xs do
-        mkLambdaFVars xs (← visit (i + 1) b) (usedLetOnly := false)
-    | .mdata _ b => return e.updateMData! (← visit (i + 1) b)
-    | .proj _ _ b => return e.updateProj! (← visit (i + 1) b)
-  visit 0 e
+      lambdaLetTelescope e fun xs b =>
+        mapreduceVisitBinders state xs fun state => do
+        let (state, b) ← visit (i + 1) state b
+        let e' ← mkLambdaFVars xs b (usedLetOnly := false)
+        return (state, e')
+    | .mdata _ b => do
+      let (state, b) ← visit (i + 1) state b
+      return (state, e.updateMData! b)
+    | .proj _ _ b => do
+      let (state, b) ← visit (i + 1) state b
+      return (state, e.updateProj! b)
+  visit 0 state e
+
+-- A map visitor function for expressions (adapted from `AbstractNestedProofs.visit`)
+-- The continuation takes as parameters:
+-- - the current depth of the expression (useful for printing/debugging)
+-- - the expression to explore
+partial def mapVisit (k : Nat → Expr → MetaM Expr) (e : Expr) : MetaM Expr := do
+  let k' i (_ : Unit) e := do
+    let e ← k i e
+    pure ((), e)
+  let (_, e) ← mapreduceVisit k' () e
+  pure e
+
+-- A reduce visitor
+partial def reduceVisit {a : Type} (k : Nat → a → Expr → MetaM a) (s : a) (e : Expr) : MetaM a := do
+  let k' i (s : a) e := do
+    let s ← k i s e
+    pure (s, e)
+  let (s, _) ← mapreduceVisit k' s e
+  pure s
 
 -- Generate a fresh user name for an anonymous proposition to introduce in the
 -- assumptions
@@ -376,16 +425,17 @@ def destEq (e : Expr) : MetaM (Expr × Expr) := do
   else throwError "Not an equality: {e}"
 
 -- Return the set of FVarIds in the expression
+-- TODO: this collects fvars introduced in the inner bindings
 partial def getFVarIds (e : Expr) (hs : HashSet FVarId := HashSet.empty) : MetaM (HashSet FVarId) := do
-  e.consumeMData.withApp fun body args => do
-  let hs := if body.isFVar then hs.insert body.fvarId! else hs
-  args.foldlM (fun hs arg => getFVarIds arg hs) hs
+  reduceVisit (fun _ (hs : HashSet FVarId) e =>
+    if e.isFVar then pure (hs.insert e.fvarId!) else pure hs)
+    hs e
 
 -- Return the set of MVarIds in the expression
 partial def getMVarIds (e : Expr) (hs : HashSet MVarId := HashSet.empty) : MetaM (HashSet MVarId) := do
-  e.consumeMData.withApp fun body args => do
-  let hs := if body.isMVar then hs.insert body.mvarId! else hs
-  args.foldlM (fun hs arg => getMVarIds arg hs) hs
+  reduceVisit (fun _ (hs : HashSet MVarId) e =>
+    if e.isMVar then pure (hs.insert e.mvarId!) else pure hs)
+    hs e
 
 -- Tactic to split on a disjunction.
 -- The expression `h` should be an fvar.