Adding traces

src/rsprocess/structure.rs

@@ -41,7 +41,7 @@ impl From<Vec<IdType>> for RSset {
 }
 
 impl RSset {
-    pub fn new() -> Self {
+    pub const fn new() -> Self {
         RSset {
             identifiers: BTreeSet::new(),
         }

src/rsprocess/transitions.rs

@@ -160,3 +160,70 @@ pub fn run_separated(
 	}
 	Ok(res)
 }
+
+
+
+fn nth_transition(
+	system: &RSsystem,
+	n: usize,
+) -> Result<Option<(RSlabel, RSsystem)>, String> {
+	let mut tr = TransitionsIterator::from(system)?;
+	Ok(tr.nth(n))
+}
+
+type Trace = Vec<(Option<Rc<RSlabel>>, Rc<RSsystem>)>;
+
+pub fn traces(
+	system: RSsystem,
+	n: usize,
+) -> Result<Vec<Trace>, String> {
+	if n == 0 {
+		return Ok(vec![])
+	}
+
+	let mut n = n;
+	let mut res : Vec<Trace> = vec![];
+	let mut current_trace: Trace = vec![(None, Rc::new(system))];
+	let mut branch = vec![0];
+	let mut depth = 0;
+	let mut new_branch = true;
+
+	loop {
+		let next_sys = nth_transition(&current_trace[depth].1,
+									  branch[depth])?;
+
+		if let Some((current_label, next_sys)) = next_sys {
+			depth += 1;
+			if depth >= branch.len() {
+				branch.push(0);
+				current_trace.push((Some(Rc::new(current_label)),
+									Rc::new(next_sys)));
+			} else {
+				branch[depth] = 0;
+				current_trace[depth] = (Some(Rc::new(current_label)),
+										Rc::new(next_sys));
+			}
+			new_branch = true;
+		} else {
+			// at the bottom of a trace, we save to res, then backtrack until
+			// we find another possible path.
+			if new_branch {
+				res.push(current_trace[0..depth].to_vec());
+				new_branch = false;
+				n -= 1;
+			}
+			if n == 0 {
+				break;
+			}
+
+			if depth == 0 {
+				break;
+			}
+
+			depth -= 1;
+			branch[depth] += 1;
+		}
+	}
+
+	Ok(res)
+}