primitive: Move `tagged_{prev,next}` to a trait

First step towards getting rid of the `untag` macro.

src/band.rs

@@ -1,8 +1,8 @@
 use petgraph::stable_graph::StableDiGraph;
 
 use crate::{
-    graph::{DotIndex, Ends, Index, Interior, Label, Weight},
+    graph::{DotIndex, Ends, Index, Interior, Label, MakePrimitive, Weight},
-    primitive::GenericPrimitive,
+    primitive::TaggedPrevTaggedNext,
 };
 
 pub struct Band {
@@ -19,10 +19,7 @@ impl Band {
         let mut next_index = Index::Dot(dot);
         let mut interior = vec![];
 
-        while let Some(index) = untag!(
+        while let Some(index) = next_index.primitive(graph).tagged_prev() {
-            next_index,
-            GenericPrimitive::new(next_index, graph).tagged_prev()
-        ) {
             interior.push(index);
             next_index = index;
         }
@@ -45,10 +42,7 @@ impl Band {
         let mut prev_index = Index::Dot(dot);
         let mut interior = vec![];
 
-        while let Some(index) = untag!(
+        while let Some(index) = prev_index.primitive(graph).tagged_next() {
-            prev_index,
-            GenericPrimitive::new(prev_index, graph).tagged_next()
-        ) {
             interior.push(index);
             prev_index = index;
         }

src/bow.rs

@@ -1,7 +1,7 @@
 use petgraph::stable_graph::StableDiGraph;
 
 use crate::graph::{BendIndex, DotIndex, Ends, Index, Interior, Label, SegIndex, Weight};
-use crate::primitive::{Bend, Dot, Seg};
+use crate::primitive::{Bend, Dot, Seg, TaggedPrevTaggedNext};
 
 #[derive(Debug, Clone, Copy)]
 pub struct Bow {

src/graph.rs

@@ -1,9 +1,12 @@
 use enum_as_inner::EnumAsInner;
 use enum_dispatch::enum_dispatch;
-use petgraph::stable_graph::NodeIndex;
+use petgraph::stable_graph::{NodeIndex, StableDiGraph};
 use std::marker::PhantomData;
 
-use crate::math::Circle;
+use crate::{
+    math::Circle,
+    primitive::{GenericPrimitive, Primitive},
+};
 
 pub trait Interior<T> {
     fn interior(&self) -> Vec<T>;
@@ -83,7 +86,12 @@ pub trait GetNodeIndex {
     fn node_index(&self) -> NodeIndex<usize>;
 }
 
-#[enum_dispatch(GetNodeIndex)]
+#[enum_dispatch]
+pub trait MakePrimitive {
+    fn primitive<'a>(&self, graph: &'a StableDiGraph<Weight, Label, usize>) -> Primitive<'a>;
+}
+
+#[enum_dispatch(GetNodeIndex, MakePrimitive)]
 #[derive(Debug, EnumAsInner, Clone, Copy, PartialEq)]
 pub enum Index {
     Dot(DotIndex),
@@ -123,5 +131,25 @@ macro_rules! untag {
 }
 
 pub type DotIndex = GenericIndex<DotWeight>;
+
+impl MakePrimitive for DotIndex {
+    fn primitive<'a>(&self, graph: &'a StableDiGraph<Weight, Label, usize>) -> Primitive<'a> {
+        Primitive::Dot(GenericPrimitive::new(*self, graph))
+    }
+}
+
 pub type SegIndex = GenericIndex<SegWeight>;
+
+impl MakePrimitive for SegIndex {
+    fn primitive<'a>(&self, graph: &'a StableDiGraph<Weight, Label, usize>) -> Primitive<'a> {
+        Primitive::Seg(GenericPrimitive::new(*self, graph))
+    }
+}
+
 pub type BendIndex = GenericIndex<BendWeight>;
+
+impl MakePrimitive for BendIndex {
+    fn primitive<'a>(&self, graph: &'a StableDiGraph<Weight, Label, usize>) -> Primitive<'a> {
+        Primitive::Bend(GenericPrimitive::new(*self, graph))
+    }
+}

src/layout.rs

@@ -12,7 +12,7 @@ use crate::graph::{
     BendIndex, BendWeight, DotIndex, DotWeight, GenericIndex, GetNodeIndex, Index, Interior, Label,
     Retag, SegIndex, SegWeight, Weight,
 };
-use crate::primitive::{GenericPrimitive, GetWeight, MakeShape};
+use crate::primitive::{GenericPrimitive, GetWeight, MakeShape, TaggedPrevTaggedNext};
 use crate::segbend::Segbend;
 use crate::shape::{Shape, ShapeTrait};
 

src/primitive.rs

@@ -11,6 +11,12 @@ use crate::graph::{
 use crate::math::{self, Circle};
 use crate::shape::{BendShape, DotShape, SegShape, Shape, ShapeTrait};
 
+#[enum_dispatch]
+pub trait TaggedPrevTaggedNext {
+    fn tagged_prev(&self) -> Option<Index>;
+    fn tagged_next(&self) -> Option<Index>;
+}
+
 #[enum_dispatch]
 pub trait GetWeight<W> {
     fn weight(&self) -> W;
@@ -21,7 +27,7 @@ pub trait MakeShape {
     fn shape(&self) -> Shape;
 }
 
-#[enum_dispatch(MakeShape)]
+#[enum_dispatch(MakeShape, TaggedPrevTaggedNext)]
 pub enum Primitive<'a> {
     Dot(Dot<'a>),
     Seg(Seg<'a>),
@@ -74,11 +80,6 @@ impl<'a, W> GenericPrimitive<'a, W> {
         None
     }
 
-    pub fn tagged_prev(&self) -> Option<Index> {
-        self.prev_node()
-            .map(|ni| self.graph.node_weight(ni).unwrap().retag(ni))
-    }
-
     fn prev_node(&self) -> Option<NodeIndex<usize>> {
         self.graph
             .neighbors_directed(self.index.node_index(), Incoming)
@@ -120,11 +121,6 @@ impl<'a, W> GenericPrimitive<'a, W> {
         None
     }
 
-    pub fn tagged_next(&self) -> Option<Index> {
-        self.next_node()
-            .map(|ni| self.graph.node_weight(ni).unwrap().retag(ni))
-    }
-
     fn next_node(&self) -> Option<NodeIndex<usize>> {
         self.graph
             .neighbors_directed(self.index.node_index(), Outgoing)
@@ -218,6 +214,18 @@ impl<'a, W> Ends<DotIndex, DotIndex> for GenericPrimitive<'a, W> {
     }
 }
 
+impl<'a, W> TaggedPrevTaggedNext for GenericPrimitive<'a, W> {
+    fn tagged_prev(&self) -> Option<Index> {
+        self.prev_node()
+            .map(|ni| self.graph.node_weight(ni).unwrap().retag(ni))
+    }
+
+    fn tagged_next(&self) -> Option<Index> {
+        self.next_node()
+            .map(|ni| self.graph.node_weight(ni).unwrap().retag(ni))
+    }
+}
+
 pub type Dot<'a> = GenericPrimitive<'a, DotWeight>;
 
 impl<'a> Dot<'a> {

src/segbend.rs

@@ -2,7 +2,7 @@ use petgraph::stable_graph::StableDiGraph;
 
 use crate::{
     graph::{BendIndex, DotIndex, Ends, Index, Interior, Label, SegIndex, Weight},
-    primitive::{Bend, Dot},
+    primitive::{Bend, Dot, TaggedPrevTaggedNext},
 };
 
 #[derive(Debug, Clone, Copy)]