Linear array storage for AST

internal/ast/builder.go

@@ -0,0 +1,58 @@
+package ast
+
+type Builder struct {
+	nodes   []Node
+	lastIdx int
+}
+
+type Reference struct {
+	idx int
+	set bool
+}
+
+func (r Reference) Valid() bool {
+	return r.set
+}
+
+func (b *Builder) Finish() *Root {
+	r := &Root{
+		nodes: b.nodes,
+	}
+	b.nodes = nil
+
+	for i := range r.nodes {
+		r.nodes[i].root = r
+	}
+
+	return r
+}
+
+func (b *Builder) Push(n Node) Reference {
+	b.lastIdx = len(b.nodes)
+	b.nodes = append(b.nodes, n)
+	return Reference{
+		idx: b.lastIdx,
+		set: true,
+	}
+}
+
+func (b *Builder) PushAndChain(n Node) Reference {
+	newIdx := len(b.nodes)
+	b.nodes = append(b.nodes, n)
+	if b.lastIdx >= 0 {
+		b.nodes[b.lastIdx].next = newIdx
+	}
+	b.lastIdx = newIdx
+	return Reference{
+		idx: b.lastIdx,
+		set: true,
+	}
+}
+
+func (b *Builder) AttachChild(parent Reference, child Reference) {
+	b.nodes[parent.idx].child = child.idx
+}
+
+func (b *Builder) Chain(from Reference, to Reference) {
+	b.nodes[from.idx].next = to.idx
+}