chain/src/atom/default.rs: Add function to print nullables

* chain/src/atom/default.rs (print_nullables): This functions prints
  the nullables nodes of an atomic language.  This is useful whe
  designing unit tests, as it enables us to know which rule positions
  are considered accepting by the underlying testing atomic language.

1 files changed, 16 insertions, 0 deletions

diff --git a/chain/src/atom/default.rs b/chain/src/atom/default.rs
index 317090e..bd71c1c 100644
--- a/chain/src/atom/default.rs
+++ b/chain/src/atom/default.rs
@@ -115,6 +115,22 @@ impl DefaultAtom {
         )?)
     }
 
+    /// Print nullable nodes.
+    pub(crate) fn print_nullables(&self) {
+        print!("printing nullables for the atom: ");
+
+        for nullable in self
+            .accepting_vec
+            .iter()
+            .enumerate()
+            .filter_map(|(index, pred)| (*pred).then(|| index))
+        {
+            print!("{nullable}, ");
+        }
+
+        println!();
+    }
+
     /// Print the underlying NFA.
     pub fn print_nfa<S: AsRef<str>>(&self, filename: S) -> Result<(), std::io::Error> {
         self.nfa.print_viz(filename.as_ref())?;