poset: to_dot also draw isolated nodes

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/src/poset.nit b/src/poset.nit
index aca5d32..0a4a4b9 100644 (file)
--- a/src/poset.nit
+++ b/src/poset.nit
@@ -133,6 +133,7 @@ class POSet[E: Object]
                #var f = stdout
                f.write "digraph \{\n"
                for x in elements.keys do
+                       f.write "\"{x}\";\n"
                        var xe = self.elements[x]
                        for y in xe.dtos do
                                if self.has_edge(y,x) then