From e1e736840ed8c925e2ff442861963250a72d4385 Mon Sep 17 00:00:00 2001
From: Sébastien Dailly <sebastien@chimrod.com>
Date: Tue, 24 Oct 2017 13:08:15 +0200
Subject: Update sheet traversal

---
 sheet.ml | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

(limited to 'sheet.ml')

diff --git a/sheet.ml b/sheet.ml
index 256a5a1..a31c9ef 100755
--- a/sheet.ml
+++ b/sheet.ml
@@ -10,8 +10,6 @@ type search = [
 
 module Raw = struct
 
-  exception Cycle
-
   module Map = Map.Make(struct
     type t = cell
     let compare (x1, y1) (x2, y2) = Pervasives.compare (y1, x1) (y2, x2)
@@ -30,7 +28,7 @@ module Raw = struct
 
   (** An empty cell which does contains nothing *)
   let empty_cell = {
-    expr = Expression.load @@ UTF8.empty;
+    expr = Expression.Undefined;
     value = None;
     sink = Cell.Set.empty;
   }
@@ -73,7 +71,7 @@ module Raw = struct
       (* If the previous value wasn't defined, update the map *)
       Some (Map.add cell { content with value = Some new_val } t)
     | Some old_value ->
-      (* If the previous value was defined, update only if both differs *)
+      (* If the previous value was defined, update only if result differs *)
       if not (ScTypes.Result.(=) new_val old_value) then
         Some (Map.add cell { content with value = Some new_val } t)
       else
@@ -89,19 +87,25 @@ module Raw = struct
     let rec successors element (parents, succ, t) = begin
 
       let content = Map.find element t in
+
       if Cell.Set.mem element parents then (
         (* if the cell has already been visited, mark it in error, and all the
            descendant *)
-        let cycle_error = Some (ScTypes.Error Cycle) in
-        let t = Map.add element { content with value = cycle_error} t
-        and set_error cell content t =
-          if content.value = cycle_error then
-            None
-          else
-            Some (Map.add cell { content with value = cycle_error} t) in
-        let succ = Cell.Set.add element succ in
-        let succ, t = traverse set_error content (succ, t) in
-        (Cell.Set.empty, succ, t)
+        let cycle_error = Some (ScTypes.Error Errors.Cycle) in
+
+        if content.value = cycle_error then
+          (* The content has already been update, do not process it again *)
+          (Cell.Set.empty, succ, t)
+        else
+          let t = Map.add element { content with value = cycle_error} t
+          and set_error cell content t =
+            if content.value = cycle_error then
+              None
+            else
+              Some (Map.add cell { content with value = cycle_error} t)
+          and succ = Cell.Set.add element succ in
+          let succ, t = traverse set_error content (succ, t) in
+          (Cell.Set.empty, succ, t)
       ) else (
         begin match f element content t with
         | None ->
@@ -117,7 +121,7 @@ module Raw = struct
         end
       )
     end in
-    let _, succ, t = Cell.Set.fold successors source.sink (Cell.Set.empty, init, t) in
+    let _, succ, t = Cell.Set.fold successors source.sink (init, init, t) in
     succ, t
   end
 
-- 
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