chain: a prototype is added.

I have an ostensibly working prototype now.

Further tests are needed to make sure that the algorithm meets the
time complexity requirement, though.

2 files changed, 142 insertions, 1 deletions

diff --git a/nfa/src/default/nfa.rs b/nfa/src/default/nfa.rs
index a23c056..8d657d5 100644
--- a/nfa/src/default/nfa.rs
+++ b/nfa/src/default/nfa.rs
@@ -212,7 +212,7 @@ impl<T: GraphLabel + Display> Nfa<T> for DefaultNFA<T> {
                 let top_label = regex.vertex_label(top_index)?;
 
                 let nfa_start = offset + 2 * top_index;
-                let nfa_end = offset + 2 * top_index + 1;
+                let nfa_end = nfa_start + 1;
 
                 match top_label {
                     RegexType::Kleene => {
diff --git a/nfa/src/default/regex.rs b/nfa/src/default/regex.rs
index c8ad370..1e3e87b 100644
--- a/nfa/src/default/regex.rs
+++ b/nfa/src/default/regex.rs
@@ -359,6 +359,147 @@ impl<T: GraphLabel> DefaultRegex<T> {
 
         Ok(result)
     }
+
+    /// Use a function to format the labels of the regular expressions
+    /// and format the entire regular expression with this aid, with a
+    /// dot at a specified position.
+    pub fn to_string_with_dot<F>(&self, mut f: F, dot_pos: usize) -> Result<String, std::fmt::Error>
+    where
+        F: FnMut(T) -> String,
+    {
+        #[derive(Copy, Clone)]
+        enum StackElement {
+            Seen(usize),
+            Unseen(usize),
+        }
+
+        impl StackElement {
+            fn index(&self) -> usize {
+                match self {
+                    Seen(index) => *index,
+                    Unseen(index) => *index,
+                }
+            }
+
+            fn is_seen(self) -> bool {
+                matches!(self, Seen(_))
+            }
+        }
+
+        use StackElement::{Seen, Unseen};
+
+        let mut result = String::new();
+
+        let mut stack: Vec<StackElement> = Vec::new();
+        let mut types = self.types.clone();
+        types.push(RegexType::Paren);
+
+        stack.push(Unseen(0));
+
+        while let Some(top) = stack.pop() {
+            let node_type = types.get(top.index()).unwrap();
+
+            match node_type {
+                RegexType::Kleene => {
+                    if !top.is_seen() {
+                        stack.push(Seen(top.index()));
+
+                        if self.degree(top.index()).unwrap() > 1 {
+                            write!(result, "(")?;
+                            stack.push(Unseen(types.len() - 1));
+                        }
+
+                        stack.extend(
+                            self.graph
+                                .children_of(top.index())
+                                .unwrap()
+                                .map(Unseen)
+                                .rev(),
+                        );
+                    } else {
+                        write!(result, "*")?;
+                    }
+                }
+                RegexType::Plus => {
+                    if !top.is_seen() {
+                        stack.push(Seen(top.index()));
+                        stack.extend(
+                            self.graph
+                                .children_of(top.index())
+                                .unwrap()
+                                .map(Unseen)
+                                .rev(),
+                        );
+                    } else {
+                        write!(result, "+")?;
+                    }
+                }
+                RegexType::Optional => {
+                    if !top.is_seen() {
+                        stack.push(Seen(top.index()));
+                        stack.extend(
+                            self.graph
+                                .children_of(top.index())
+                                .unwrap()
+                                .map(Unseen)
+                                .rev(),
+                        );
+                    } else {
+                        write!(result, "?")?;
+                    }
+                }
+                RegexType::Or => {
+                    if !top.is_seen() {
+                        write!(result, "(")?;
+
+                        let len = self.len();
+
+                        stack.push(Unseen(types.len() - 1));
+
+                        for (child_index, child) in self
+                            .graph
+                            .children_of(top.index())
+                            .unwrap()
+                            .enumerate()
+                            .rev()
+                        {
+                            if child_index != len - 1 && child_index != 0 {
+                                stack.push(Unseen(child));
+                                stack.push(Seen(top.index()));
+                            } else {
+                                stack.push(Unseen(child));
+                            }
+                        }
+                    } else {
+                        write!(result, "|")?;
+                    }
+                }
+                RegexType::Paren => {
+                    write!(result, ")")?;
+                }
+                RegexType::Empty => {
+                    stack.extend(
+                        self.graph
+                            .children_of(top.index())
+                            .unwrap()
+                            .map(Unseen)
+                            .rev(),
+                    );
+
+                    if self.graph.is_empty_node(top.index()).unwrap() {
+                        write!(result, "ε")?;
+                    }
+                }
+                RegexType::Lit(label) => write!(result, "{}", f(*label))?,
+            }
+
+            if top.index() == dot_pos {
+                write!(result, " · ")?;
+            }
+        }
+
+        Ok(result)
+    }
 }
 
 impl<T: GraphLabel + Display + Debug> Display for DefaultRegex<T> {