Modify graph

src/graph/mod.rs

@@ -1,12 +1,9 @@
-use petgraph::{
-    graph::{DiGraph, NodeIndex},
-    visit::EdgeRef,
-};
+use petgraph::{graph::NodeIndex, stable_graph::StableDiGraph, visit::EdgeRef};
 use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 use std::{any::Any, collections::VecDeque};
 
-type NodeGraph = DiGraph<ErasedNode, (), u32>;
+type NodeGraph = StableDiGraph<ErasedNode, (), u32>;
 
 pub struct Graph<Output> {
     // we treat this as a StableGraph, since nodes are never removed
@@ -18,14 +15,13 @@ pub struct Graph<Output> {
 impl<Output: Clone + 'static> Graph<Output> {
     pub fn new() -> Self {
         Self {
-            node_graph: Rc::new(RefCell::new(DiGraph::new())),
+            node_graph: Rc::new(RefCell::new(StableDiGraph::new())),
             output: None,
             output_type: std::marker::PhantomData,
         }
     }
 
     pub fn set_output<R: Rule<Output> + 'static>(&mut self, rule: R) {
-        assert!(self.output.is_none(), "cannot replace graph output");
         let input = self.add_rule(rule);
         self.output = Some(input.node_idx);
     }
@@ -70,7 +66,7 @@ impl<Output: Clone + 'static> Graph<Output> {
         }
 
         let graph = self.node_graph.borrow();
-        let indices = graph.node_indices();
+        let indices = graph.node_indices().collect::<Vec<_>>();
         drop(graph);
         let mut edges = vec![];
         for idx in indices {
@@ -84,6 +80,8 @@ impl<Output: Clone + 'static> Graph<Output> {
             self.node_graph.borrow_mut().add_edge(source, dest, ());
         }
 
+        // TODO: remove nodes not connected to output
+
         let sorted = petgraph::algo::toposort(&*self.node_graph.borrow(), None);
         if let Err(_cycle) = sorted {
             // TODO: actually build a vec describing the cycle path for debugging
@@ -148,6 +146,30 @@ impl<Output: Clone + 'static> FrozenGraph<Output> {
         let node = &graph[self.output].expect_type::<Output>();
         node.value()
     }
+
+    pub fn modify<F>(&mut self, mut f: F) -> Result<(), GraphFreezeError>
+    where
+        F: FnMut(&mut Graph<Output>) -> (),
+    {
+        // Clear the edges before modifying so that re-freezing results in a graph with up-to-date edges.
+        let mut graph = self.node_graph.borrow_mut();
+        graph.clear_edges();
+        drop(graph);
+
+        let mut graph = Graph {
+            node_graph: Rc::clone(&self.node_graph),
+            output: Some(self.output),
+            output_type: std::marker::PhantomData,
+        };
+        f(&mut graph);
+        match graph.freeze() {
+            Ok(g) => {
+                *self = g;
+                Ok(())
+            }
+            Err(e) => Err(e),
+        }
+    }
 }
 
 pub struct Input<T> {
@@ -484,4 +506,18 @@ mod tests {
             Ok(_) => assert!(false, "shouldn't have frozen graph"),
         }
     }
+
+    #[test]
+    fn modify_graph() {
+        let mut graph = Graph::new();
+        graph.set_output(ConstantRule(1));
+        let mut frozen = graph.freeze().unwrap();
+        assert_eq!(frozen.evaluate(), 1);
+        frozen
+            .modify(|g| {
+                g.set_output(ConstantRule(2));
+            })
+            .expect("modify");
+        assert_eq!(frozen.evaluate(), 2);
+    }
 }