lollipop operator, fixed but in grammar-lalrpop for environment parsing

src/rsprocess/perpetual.rs

@@ -0,0 +1,55 @@
+#![allow(dead_code)]
+
+use std::rc::Rc;
+
+use super::classical::compute_all_owned;
+use super::translator::IdType;
+use super::structure::{RSsystem, RSprocess, RSset, RSreaction};
+
+fn split<'a>(set: &'a RSset, trace: &'a [RSset]) -> Option<(&'a[RSset], &'a[RSset])> {
+    let position = trace.iter().rposition(|x| x == set);
+    position.map(|pos| trace.split_at(pos))
+}
+
+fn find_loop(rs: &Rc<Vec<RSreaction>>, e: RSset, q: &RSset) -> (Vec<RSset>, Vec<RSset>) {
+    let mut e = e;
+    let mut trace = vec![];
+    loop {
+	if let Some((prefix, hoop)) = split(&e, &trace) {
+	    return (prefix.to_vec(), hoop.to_vec());
+	} else {
+	    let t = e.union(q);
+	    let p = compute_all_owned(&t, rs);
+	    trace.push(e.clone());
+	    e = p;
+	}
+    }
+}
+
+// see lollipop
+pub fn lollipops(system: RSsystem) -> Vec<(Vec<RSset>, Vec<RSset>)> {
+    fn filter_delta<'a>(x: (&IdType, &'a RSprocess)) -> Option<&'a RSset> {
+	use super::structure::RSprocess::*;
+	let (id, rest) = x;
+	match rest {
+	    EntitySet{ entities, next_process} => {
+		match &**next_process {
+		    RecursiveIdentifier{ identifier } if identifier == id => {
+			Some(entities)
+		    },
+		    _ => None
+		}
+	    },
+	    _ => None
+	}
+    }
+
+    // FIXME: what? i think we are only interested in "x", not all symbols that
+    // satisfy X = pre(Q, rec(X))
+    let filtered = system.get_delta().iter().filter_map(filter_delta);
+
+    filtered.map(|q| find_loop(system.get_reaction_rules(),
+			       system.get_available_entities().clone(),
+			       q)
+    ).collect::<Vec<_>>()
+}