lib: introduce service `depth` in PosetElement

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --git a/lib/poset.nit b/lib/poset.nit
index aea40bb..fc6090f 100644 (file)
--- a/lib/poset.nit
+++ b/lib/poset.nit
@@ -230,4 +230,20 @@ class POSetElement[E: Object]
        do
                return t != self.element and self.tos.has(t)
        end
+
+       # The length of the shortest path to the root of the poset hierarchy
+       fun depth: Int do
+               if direct_greaters.is_empty then
+                       return 0
+               end
+               var min = -1
+               for p in direct_greaters do
+                       var d = poset[p].depth + 1
+                       if min == -1 or d < min then
+                               min = d
+                       end
+               end
+               return min
+
+       end
 end