Finally produced the first correct forest

Finally the prototype parser has produced the first correct forest.
It is my first time to generate a correct forest, in fact, ever since
the beginning of this project.

1 files changed, 45 insertions, 2 deletions

diff --git a/graph/src/labelled/binary.rs b/graph/src/labelled/binary.rs
index 201dda2..4ec7378 100644
--- a/graph/src/labelled/binary.rs
+++ b/graph/src/labelled/binary.rs
@@ -203,8 +203,51 @@ impl<T: GraphLabel> Graph for PLGraph<T> {
         unimplemented!("use a `PLGBuilderMut` instead")
     }
 
-    fn print_viz(&self, _filename: &str) -> Result<(), std::io::Error> {
-        todo!()
+    fn print_viz(&self, filename: &str) -> Result<(), std::io::Error> {
+        let filename = format!("output/{filename}");
+
+        let preamble = "digraph nfa {
+    fontname=\"Helvetica,Arial,sans-serif\"
+    node [fontname=\"Helvetica,Arial,sans-serif\"]
+    edge [fontname=\"Helvetica,Arial,sans-serif\"]
+    rankdir=LR;\n";
+
+        let mut post = String::new();
+
+        for node in self.nodes() {
+            post.push_str(&format!(
+                "    {node} [label = \"{}\"]\n",
+                match self.vertex_label(node) {
+                    Ok(Some(label)) => {
+                        format!("{label}")
+                    }
+                    _ => {
+                        " ε ".to_owned()
+                    }
+                }
+            ));
+        }
+
+        for (source, target) in self.edges() {
+            post.push_str(&format!("    {source} -> {target}\n"));
+        }
+
+        post.push_str("}\n");
+
+        let result = format!("{preamble}{post}");
+
+        if std::fs::metadata(&filename).is_ok() {
+            std::fs::remove_file(&filename)?;
+        }
+
+        let mut file = std::fs::File::options()
+            .write(true)
+            .create(true)
+            .open(&filename)?;
+
+        use std::io::Write;
+
+        file.write_all(result.as_bytes())
     }
 }