fix multiple nested ctrs

src/ast.rs

@@ -146,10 +146,10 @@ pub const MAX_ADT_FIELDS: usize = MAX_ARITY - 1;
 
 impl Net {
   pub fn trees(&self) -> impl Iterator<Item = &Tree> {
-    std::iter::once(&self.root).chain(self.redexes.iter().map(|(x, y)| [x, y]).flatten())
+    std::iter::once(&self.root).chain(self.redexes.iter().flat_map(|(x, y)| [x, y]))
   }
   pub fn trees_mut(&mut self) -> impl Iterator<Item = &mut Tree> {
-    std::iter::once(&mut self.root).chain(self.redexes.iter_mut().map(|(x, y)| [x, y]).flatten())
+    std::iter::once(&mut self.root).chain(self.redexes.iter_mut().flat_map(|(x, y)| [x, y]))
   }
 }
 

src/transform/eta_reduce.rs

@@ -1,19 +1,22 @@
-use std::collections::HashMap;
+use std::{collections::HashMap, ops::RangeFrom};
 
 use crate::ast::{Net, Tree};
 
-/// Converts (x y), (x y) into x, x
+/// Converts `(x y), (x y)` into `x, x`.
 impl Net {
   pub fn eta_reduce(&mut self) {
     let mut phase1 = Phase1::default();
-    phase1.walk_and_sort_net(self);
-    println!("{:?}", phase1.gaps);
-    let mut phase2 = Phase2 { gaps: phase1.gaps };
-    phase2.reduce_net(self);
+    for tree in self.trees() {
+      phase1.walk_tree(tree);
+    }
+    let mut phase2 = Phase2 { nodes: phase1.nodes, index: 0 .. };
+    for tree in self.trees_mut() {
+      phase2.reduce_tree(tree);
+    }
   }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum NodeType {
   Var(isize),
   Ctr(u16),
@@ -24,103 +27,81 @@ enum NodeType {
 #[derive(Default)]
 struct Phase1<'a> {
   vars: HashMap<&'a str, usize>,
-  gaps: Vec<NodeType>,
+  nodes: Vec<NodeType>,
 }
 
 impl<'a> Phase1<'a> {
-  fn walk_and_sort_net(&mut self, net: &'a mut Net) {
-    self.walk_and_sort_tree(&mut net.root);
-    for (a, b) in net.redexes.iter_mut() {
-      self.walk_and_sort_tree(a);
-      self.walk_and_sort_tree(b);
-    }
-  }
-  fn walk_and_sort_tree(&mut self, tree: &'a mut Tree) {
+  fn walk_tree(&mut self, tree: &'a Tree) {
     match tree {
       Tree::Ctr { lab, ports } => {
         let last_port = ports.len() - 1;
-        for (idx, i) in ports.iter_mut().enumerate() {
+        for (idx, i) in ports.iter().enumerate() {
           if idx != last_port {
-            self.gaps.push(NodeType::Ctr(*lab));
+            self.nodes.push(NodeType::Ctr(*lab));
           }
-          self.walk_and_sort_tree(i);
+          self.walk_tree(i);
         }
       }
       Tree::Var { nam } => {
         let nam: &str = &*nam;
         if let Some(i) = self.vars.get(nam) {
-          let j = self.gaps.len() as isize;
-          self.gaps.push(NodeType::Var(*i as isize - j));
-          self.gaps[*i] = NodeType::Var(j - *i as isize);
+          let j = self.nodes.len() as isize;
+          self.nodes.push(NodeType::Var(*i as isize - j));
+          self.nodes[*i] = NodeType::Var(j - *i as isize);
         } else {
-          self.vars.insert(nam, self.gaps.len());
-          self.gaps.push(NodeType::Hole);
+          self.vars.insert(nam, self.nodes.len());
+          self.nodes.push(NodeType::Hole);
         }
       }
       _ => {
-        self.gaps.push(NodeType::Other);
-        for i in tree.children_mut() {
-          self.walk_and_sort_tree(i);
+        self.nodes.push(NodeType::Other);
+        for i in tree.children() {
+          self.walk_tree(i);
         }
       }
     }
   }
 }
 
 struct Phase2 {
-  gaps: Vec<NodeType>,
+  nodes: Vec<NodeType>,
+  index: RangeFrom<usize>,
 }
 
 impl Phase2 {
-  fn reduce_net(&mut self, net: &mut Net) {
-    let mut index = 0;
-    self.reduce_tree(&mut net.root, &mut index);
-    for (a, b) in net.redexes.iter_mut() {
-      self.reduce_tree(a, &mut index);
-      self.reduce_tree(b, &mut index);
+  fn reduce_ctr(&mut self, lab: u16, ports: &mut Vec<Tree>, skip: usize) -> NodeType {
+    if skip == ports.len() {
+      return NodeType::Other;
     }
-  }
-  fn reduce_tree(&mut self, tree: &mut Tree, index: &mut usize) {
-    match tree {
-      ctr @ Tree::Ctr { .. } => {
-        let Tree::Ctr { lab, ports } = ctr else { unreachable!() };
-        // reduce from the inside of the n-ary node to the outside
-        let mut indices = vec![];
-        let last_port = ports.len() - 1;
-        for (idx, i) in ports.iter_mut().enumerate() {
-          indices.push(*index);
-          if idx != last_port {
-            *index += 1;
-          }
-          self.reduce_tree(i, index);
-        }
-        while indices.len() > 1 {
-          let tail_var = indices.pop().unwrap();
-          let head_ctr = indices.pop().unwrap();
-          let head_var = head_ctr + 1;
-          if let (NodeType::Var(off1), NodeType::Var(off2)) = (&self.gaps[head_var], &self.gaps[tail_var]) {
-            if off1 == off2 {
-              if let NodeType::Ctr(other_lab) = &self.gaps[head_ctr.strict_add_signed(*off1)] {
-                if other_lab == lab {
-                  indices.push(head_var);
-                  ports.pop();
-                  continue;
-                }
-              }
-            }
-          }
-          break;
-        }
-        if ports.len() == 1 {
-          *ctr = ports.pop().unwrap();
+    if skip == ports.len() - 1 {
+      return self.reduce_tree(&mut ports[skip]);
+    }
+    let head_index = self.index.next().unwrap();
+    let a = self.reduce_tree(&mut ports[skip]);
+    let b = self.reduce_ctr(lab, ports, skip + 1);
+    if a == b {
+      if let NodeType::Var(delta) = a {
+        if self.nodes[head_index.wrapping_add_signed(delta)] == NodeType::Ctr(lab) {
+          ports.pop();
+          return NodeType::Var(delta);
         }
       }
-      tree => {
-        *index += 1;
-        for i in tree.children_mut() {
-          self.reduce_tree(i, index);
-        }
+    }
+    NodeType::Ctr(lab)
+  }
+  fn reduce_tree(&mut self, tree: &mut Tree) -> NodeType {
+    if let Tree::Ctr { lab, ports } = tree {
+      let ty = self.reduce_ctr(*lab, ports, 0);
+      if ports.len() == 1 {
+        *tree = ports.pop().unwrap();
+      }
+      ty
+    } else {
+      let index = self.index.next().unwrap();
+      for i in tree.children_mut() {
+        self.reduce_tree(i);
       }
+      self.nodes[index]
     }
   }
 }

tests/transform.rs

@@ -78,4 +78,7 @@ pub fn test_eta() {
   a
   & (a c) ~ c
   "###);
+  assert_display_snapshot!(parse_and_reduce("((a b) [a b])"), @"((a b) [a b])");
+  assert_display_snapshot!(parse_and_reduce("((a b c) b c)"), @"((a b) b)");
+  assert_display_snapshot!(parse_and_reduce("([(a b) (c d)] [(a b) (c d)])"), @"(a a)");
 }