forest seems to be completed

I seem to have finished the implementation of forests.  Now it remains
the implementation of the chain-rule machine, of which I have a rough
plan now.

1 files changed, 3 insertions, 0 deletions

diff --git a/grammar/Cargo.toml b/grammar/Cargo.toml
index 20c4b48..793ab5a 100644
--- a/grammar/Cargo.toml
+++ b/grammar/Cargo.toml
@@ -12,6 +12,9 @@ default = []
 # some grammars for testing.
 test-helper = []
 
+# This flag controls whether to print GraphViz files during testing.
+test-print-viz = []
+
 [dependencies]
 nfa = { path = "../nfa" }
 graph = { path = "../graph" }