Linear array storage for AST

internal/ast/ast.go

@@ -2,182 +2,103 @@ package ast
 
 import (
 	"fmt"
-	"strings"
 )
 
-type Kind int
+// Iterator starts uninitialized, you need to call Next() first.
-
+//
-const (
+// For example:
-	// meta
+//
-	Invalid Kind = iota
+// it := n.Children()
-	Comment
+// for it.Next() {
-	Key
+// 		it.Node()
-
+// }
-	// top level structures
+type Iterator interface {
-	Table
+	// Next moves the iterator forward and returns true if points to a node, false
-	ArrayTable
+	// otherwise.
-	KeyValue
+	Next() bool
-
+	// Node returns a copy of the node pointed at by the iterator.
-	// containers values
+	Node() Node
-	Array
-	InlineTable
-
-	// values
-	String
-	Bool
-	Float
-	Integer
-	LocalDate
-	LocalDateTime
-	DateTime
-	Time
-)
-
-func (k Kind) String() string {
-	switch k {
-	case Invalid:
-		return "Invalid"
-	case Comment:
-		return "Comment"
-	case Key:
-		return "Key"
-	case Table:
-		return "Table"
-	case ArrayTable:
-		return "ArrayTable"
-	case KeyValue:
-		return "KeyValue"
-	case Array:
-		return "Array"
-	case InlineTable:
-		return "InlineTable"
-	case String:
-		return "String"
-	case Bool:
-		return "Bool"
-	case Float:
-		return "Float"
-	case Integer:
-		return "Integer"
-	case LocalDate:
-		return "LocalDate"
-	case LocalDateTime:
-		return "LocalDateTime"
-	case DateTime:
-		return "DateTime"
-	case Time:
-		return "Time"
-	}
-	panic(fmt.Errorf("Kind.String() not implemented for '%d'", k))
 }
 
-type Root []Node
+type chainIterator struct {
-
+	started bool
-// Dot returns a dot representation of the AST for debugging.
+	node    Node
-func (r Root) Sdot() string {
-	type edge struct {
-		from     int
-		childIdx int
-		to       int
-	}
-
-	var nodes []Node
-	var edges []edge // indexes into nodes
-
-	nodes = append(nodes, Node{
-		Kind:     Invalid,
-		Data:     []byte(`ROOT`),
-		Children: r,
-	})
-
-	var processNode func(int, int, *Node)
-	processNode = func(parentIdx int, childIdx int, node *Node) {
-		idx := len(nodes)
-		nodes = append(nodes, *node)
-		edges = append(edges, edge{
-			from:     parentIdx,
-			childIdx: childIdx,
-			to:       idx,
-		})
-
-		for i, c := range node.Children {
-			processNode(idx, i, &c)
-		}
-	}
-
-	for i, n := range r {
-		processNode(0, i, &n)
-	}
-
-	var b strings.Builder
-
-	b.WriteString("digraph tree {\n")
-	b.WriteString("\tnode [shape=record];\n")
-
-	for i, node := range nodes {
-		label := ""
-		attrs := map[string]string{}
-
-		if i == 0 {
-			var ports []string
-			for i := 0; i < len(node.Children); i++ {
-				ports = append(ports, fmt.Sprintf("<f%d> %d", i, i))
-			}
-			joinedPorts := strings.Join(ports, "|")
-			label = fmt.Sprintf("{ROOT|{%s}}", joinedPorts)
-		} else {
-			fields := []string{node.Kind.String()}
-			if len(node.Data) > 0 {
-				fields = append(fields, string(node.Data))
-			}
-
-			var ports []string
-			for i := 0; i < len(node.Children); i++ {
-				ports = append(ports, fmt.Sprintf("<f%d> %d", i, i))
-			}
-			joinedPorts := strings.Join(ports, "|")
-
-			joinedFields := strings.Join(fields, "|")
-			label = fmt.Sprintf("{{%s}", joinedFields)
-			if len(ports) > 0 {
-				label += fmt.Sprintf("|{%s}", joinedPorts)
-			}
-			label += "}"
-			if node.Kind == Invalid {
-				attrs["style"] = "filled"
-				attrs["fillcolor"] = "red"
-			}
-		}
-
-		_, _ = fmt.Fprintf(&b, "\tnode%d [label=\"%s\"", i, label)
-		for k, v := range attrs {
-			_, _ = fmt.Fprintf(&b, ", %s=\"%s\"", k, v)
-		}
-		_, _ = fmt.Fprintf(&b, "];\n")
-	}
-
-	b.WriteString("\n")
-
-	for _, e := range edges {
-		_, _ = fmt.Fprintf(&b, "\tnode%d:f%d -> node%d;\n", e.from, e.childIdx, e.to)
-	}
-
-	b.WriteString("}")
-
-	return b.String()
 }
 
+func (c *chainIterator) Next() bool {
+	if !c.started {
+		c.started = true
+	} else if c.node.Valid() {
+		c.node = c.node.Next()
+	}
+	return c.node.Valid()
+}
+
+func (c *chainIterator) Node() Node {
+	return c.node
+}
+
+type Root struct {
+	nodes []Node
+}
+
+func (r *Root) Iterator() Iterator {
+	it := &chainIterator{}
+	if len(r.nodes) > 0 {
+		it.node = r.nodes[0]
+	}
+	return it
+}
+
+func (r *Root) Reset() {
+	r.nodes = r.nodes[:0]
+}
+
+func (r *Root) at(idx int) Node {
+	// TODO: unsafe to point to the node directly
+	return r.nodes[idx]
+}
+
+// Arrays have one child per element in the array.
+// InlineTables have one child per key-value pair in the table.
+// KeyValues have at least two children. The first one is the value. The
+// rest make a potentially dotted key.
+// Table and Array table have one child per element of the key they
+// represent (same as KeyValue, but without the last node being the value).
+// children []Node
 type Node struct {
 	Kind Kind
 	Data []byte // Raw bytes from the input
 
-	// Arrays have one child per element in the array.
+	// next idx (in the root array). 0 if last of the collection.
-	// InlineTables have one child per key-value pair in the table.
+	next int
-	// KeyValues have at least two children. The last one is the value. The
+	// child idx (in the root array). 0 if no child.
-	// rest make a potentially dotted key.
+	child int
-	// Table and Array table have one child per element of the key they
+	// pointer to the root array
-	// represent (same as KeyValue, but without the last node being the value).
+	root *Root
-	Children []Node
+}
+
+// Next returns a copy of the next node, or an invalid Node if there is no
+// next node.
+func (n Node) Next() Node {
+	if n.next <= 0 {
+		return NoNode
+	}
+	return n.root.at(n.next)
+}
+
+// Child returns a copy of the first child node of this node. Other children
+// can be accessed calling Next on the first child.
+// Returns an invalid Node if there is none.
+func (n Node) Child() Node {
+	if n.child <= 0 {
+		return NoNode
+	}
+	return n.root.at(n.child)
+}
+
+func (n Node) Valid() bool {
+	return n.Kind != Invalid
 }
 
 var NoNode = Node{}
@@ -186,15 +107,16 @@ var NoNode = Node{}
 // otherwise.
 // They are guaranteed to be all be of the Kind Key. A simple key would return
 // just one element.
-func (n *Node) Key() []Node {
+func (n *Node) Key() Iterator {
 	switch n.Kind {
 	case KeyValue:
-		if len(n.Children) < 2 {
+		value := n.Child()
-			panic(fmt.Errorf("KeyValue should have at least two children, not %d", len(n.Children)))
+		if !value.Valid() {
+			panic(fmt.Errorf("KeyValue should have at least two children"))
 		}
-		return n.Children[:len(n.Children)-1]
+		return &chainIterator{node: value.Next()}
 	case Table, ArrayTable:
-		return n.Children
+		return &chainIterator{node: n.Child()}
 	default:
 		panic(fmt.Errorf("Key() is not supported on a %s", n.Kind))
 	}
@@ -203,15 +125,16 @@ func (n *Node) Key() []Node {
 // Value returns a pointer to the value node of a KeyValue.
 // Guaranteed to be non-nil.
 // Panics if not called on a KeyValue node, or if the Children are malformed.
-func (n *Node) Value() *Node {
+func (n Node) Value() Node {
 	assertKind(KeyValue, n)
-	if len(n.Children) < 2 {
+	return n.Child()
-		panic(fmt.Errorf("KeyValue should have at least two children, not %d", len(n.Children)))
-	}
-	return &n.Children[len(n.Children)-1]
 }
 
-func assertKind(k Kind, n *Node) {
+func (n Node) Children() Iterator {
+	return &chainIterator{node: n.Child()}
+}
+
+func assertKind(k Kind, n Node) {
 	if n.Kind != k {
 		panic(fmt.Errorf("method was expecting a %s, not a %s", k, n.Kind))
 	}

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
+}

internal/ast/kind.go

@@ -0,0 +1,69 @@
+package ast
+
+import "fmt"
+
+type Kind int
+
+const (
+	// meta
+	Invalid Kind = iota
+	Comment
+	Key
+
+	// top level structures
+	Table
+	ArrayTable
+	KeyValue
+
+	// containers values
+	Array
+	InlineTable
+
+	// values
+	String
+	Bool
+	Float
+	Integer
+	LocalDate
+	LocalDateTime
+	DateTime
+	Time
+)
+
+func (k Kind) String() string {
+	switch k {
+	case Invalid:
+		return "Invalid"
+	case Comment:
+		return "Comment"
+	case Key:
+		return "Key"
+	case Table:
+		return "Table"
+	case ArrayTable:
+		return "ArrayTable"
+	case KeyValue:
+		return "KeyValue"
+	case Array:
+		return "Array"
+	case InlineTable:
+		return "InlineTable"
+	case String:
+		return "String"
+	case Bool:
+		return "Bool"
+	case Float:
+		return "Float"
+	case Integer:
+		return "Integer"
+	case LocalDate:
+		return "LocalDate"
+	case LocalDateTime:
+		return "LocalDateTime"
+	case DateTime:
+		return "DateTime"
+	case Time:
+		return "Time"
+	}
+	panic(fmt.Errorf("Kind.String() not implemented for '%d'", k))
+}

parser.go

@@ -10,11 +10,11 @@ import (
 )
 
 type parser struct {
-	tree ast.Root
+	builder ast.Builder
 }
 
 func (p *parser) parse(b []byte) error {
-	b, err := p.parseExpression(b)
+	last, b, err := p.parseExpression(b)
 	if err != nil {
 		return err
 	}
@@ -24,10 +24,15 @@ func (p *parser) parse(b []byte) error {
 			return err
 		}
 
-		b, err = p.parseExpression(b)
+		var next ast.Reference
+		next, b, err = p.parseExpression(b)
 		if err != nil {
 			return err
 		}
+		if next.Valid() {
+			p.builder.Chain(last, next)
+			last = next
+		}
 	}
 	return nil
 }
@@ -43,49 +48,48 @@ func (p *parser) parseNewline(b []byte) ([]byte, error) {
 	return nil, fmt.Errorf("expected newline but got %#U", b[0])
 }
 
-func (p *parser) parseExpression(b []byte) ([]byte, error) {
+func (p *parser) parseExpression(b []byte) (ast.Reference, []byte, error) {
 	//expression =  ws [ comment ]
 	//expression =/ ws keyval ws [ comment ]
 	//expression =/ ws table ws [ comment ]
 
+	var ref ast.Reference
+
 	b = p.parseWhitespace(b)
 
 	if len(b) == 0 {
-		return b, nil
+		return ref, b, nil
 	}
 
 	if b[0] == '#' {
 		_, rest, err := scanComment(b)
-		return rest, err
+		return ref, rest, err
 	}
 	if b[0] == '\n' || b[0] == '\r' {
-		return b, nil
+		return ref, b, nil
 	}
 
 	var err error
-	var node ast.Node
 	if b[0] == '[' {
-		node, b, err = p.parseTable(b)
+		ref, b, err = p.parseTable(b)
 	} else {
-		node, b, err = p.parseKeyval(b)
+		ref, b, err = p.parseKeyval(b)
 	}
 	if err != nil {
-		return nil, err
+		return ref, nil, err
 	}
 
-	p.tree = append(p.tree, node)
-
 	b = p.parseWhitespace(b)
 
 	if len(b) > 0 && b[0] == '#' {
 		_, rest, err := scanComment(b)
-		return rest, err
+		return ref, rest, err
 	}
 
-	return b, nil
+	return ref, b, nil
 }
 
-func (p *parser) parseTable(b []byte) (ast.Node, []byte, error) {
+func (p *parser) parseTable(b []byte) (ast.Reference, []byte, error) {
 	//table = std-table / array-table
 	if len(b) > 1 && b[1] == '[' {
 		return p.parseArrayTable(b)
@@ -93,90 +97,95 @@ func (p *parser) parseTable(b []byte) (ast.Node, []byte, error) {
 	return p.parseStdTable(b)
 }
 
-func (p *parser) parseArrayTable(b []byte) (ast.Node, []byte, error) {
+func (p *parser) parseArrayTable(b []byte) (ast.Reference, []byte, error) {
 	//array-table = array-table-open key array-table-close
 	//array-table-open  = %x5B.5B ws  ; [[ Double left square bracket
 	//array-table-close = ws %x5D.5D  ; ]] Double right square bracket
 
-	node := ast.Node{
+	ref := p.builder.Push(ast.Node{
 		Kind: ast.ArrayTable,
-	}
+	})
 
 	b = b[2:]
 	b = p.parseWhitespace(b)
 	k, b, err := p.parseKey(b)
 	if err != nil {
-		return node, nil, err
+		return ref, nil, err
 	}
-	node.Children = k
+	p.builder.AttachChild(ref, k)
 	b = p.parseWhitespace(b)
 	b, err = expect(']', b)
 	if err != nil {
-		return node, nil, err
+		return ref, nil, err
 	}
 	b, err = expect(']', b)
-	return node, b, err
+	return ref, b, err
 }
 
-func (p *parser) parseStdTable(b []byte) (ast.Node, []byte, error) {
+func (p *parser) parseStdTable(b []byte) (ast.Reference, []byte, error) {
 	//std-table = std-table-open key std-table-close
 	//std-table-open  = %x5B ws     ; [ Left square bracket
 	//std-table-close = ws %x5D     ; ] Right square bracket
 
-	node := ast.Node{
+	ref := p.builder.Push(ast.Node{
 		Kind: ast.Table,
-	}
+	})
 
 	b = b[1:]
 	b = p.parseWhitespace(b)
 	key, b, err := p.parseKey(b)
 	if err != nil {
-		return ast.NoNode, nil, err
+		return ref, nil, err
 	}
-	node.Children = key
+
+	p.builder.AttachChild(ref, key)
+
 	b = p.parseWhitespace(b)
 
 	b, err = expect(']', b)
 
-	return node, b, err
+	return ref, b, err
 }
 
-func (p *parser) parseKeyval(b []byte) (ast.Node, []byte, error) {
+func (p *parser) parseKeyval(b []byte) (ast.Reference, []byte, error) {
 	//keyval = key keyval-sep val
 
-	node := ast.Node{
+	ref := p.builder.Push(ast.Node{
 		Kind: ast.KeyValue,
-	}
+	})
 
 	key, b, err := p.parseKey(b)
 	if err != nil {
-		return ast.NoNode, nil, err
+		return ast.Reference{}, nil, err
 	}
-	node.Children = append(node.Children, key...)
 
 	//keyval-sep = ws %x3D ws ; =
 
 	b = p.parseWhitespace(b)
 	b, err = expect('=', b)
 	if err != nil {
-		return ast.NoNode, nil, err
+		return ast.Reference{}, nil, err
 	}
 	b = p.parseWhitespace(b)
 
-	valNode, b, err := p.parseVal(b)
+	valRef, b, err := p.parseVal(b)
-	if err == nil {
+	if err != nil {
-		node.Children = append(node.Children, valNode)
+		return ref, b, err
 	}
-	return node, b, err
+	p.builder.Chain(valRef, key)
+	p.builder.AttachChild(ref, valRef)
+
+	return ref, b, err
 }
 
-func (p *parser) parseVal(b []byte) (ast.Node, []byte, error) {
+func (p *parser) parseVal(b []byte) (ast.Reference, []byte, error) {
 	// val = string / boolean / array / inline-table / date-time / float / integer
+	var ref ast.Reference
+
 	if len(b) == 0 {
-		return ast.NoNode, nil, fmt.Errorf("expected value, not eof")
+		return ref, nil, fmt.Errorf("expected value, not eof")
 	}
 
-	node := ast.Node{}
 	var err error
 	c := b[0]
 
@@ -189,10 +198,12 @@ func (p *parser) parseVal(b []byte) (ast.Node, []byte, error) {
 			v, b, err = p.parseBasicString(b)
 		}
 		if err == nil {
-			node.Kind = ast.String
+			ref = p.builder.Push(ast.Node{
-			node.Data = v
+				Kind: ast.String,
+				Data: v,
+			})
 		}
-		return node, b, err
+		return ref, b, err
 	case '\'':
 		var v []byte
 		if scanFollowsMultilineLiteralStringDelimiter(b) {
@@ -201,35 +212,36 @@ func (p *parser) parseVal(b []byte) (ast.Node, []byte, error) {
 			v, b, err = p.parseLiteralString(b)
 		}
 		if err == nil {
-			node.Kind = ast.String
+			ref = p.builder.Push(ast.Node{
-			node.Data = v
+				Kind: ast.String,
+				Data: v,
+			})
 		}
-		return node, b, err
+		return ref, b, err
 	case 't':
 		if !scanFollowsTrue(b) {
-			return node, nil, fmt.Errorf("expected 'true'")
+			return ref, nil, fmt.Errorf("expected 'true'")
 		}
-		node.Kind = ast.Bool
+		ref = p.builder.Push(ast.Node{
-		node.Data = b[:4]
+			Kind: ast.Bool,
-		return node, b[4:], nil
+			Data: b[:4],
+		})
+		return ref, b[4:], nil
 	case 'f':
 		if !scanFollowsFalse(b) {
-			return node, nil, fmt.Errorf("expected 'false'")
+			return ast.Reference{}, nil, fmt.Errorf("expected 'false'")
 		}
-		node.Kind = ast.Bool
+		ref = p.builder.Push(ast.Node{
-		node.Data = b[:5]
+			Kind: ast.Bool,
-		return node, b[5:], nil
+			Data: b[:5],
+		})
+		return ref, b[5:], nil
 	case '[':
-		node.Kind = ast.Array
+		return p.parseValArray(b)
-		b, err := p.parseValArray(&node, b)
-		return node, b, err
 	case '{':
-		node.Kind = ast.InlineTable
+		return p.parseInlineTable(b)
-		b, err := p.parseInlineTable(&node, b)
-		return node, b, err
 	default:
-		b, err = p.parseIntOrFloatOrDateTime(&node, b)
+		return p.parseIntOrFloatOrDateTime(b)
-		return node, b, err
 	}
 }
 
@@ -241,16 +253,22 @@ func (p *parser) parseLiteralString(b []byte) ([]byte, []byte, error) {
 	return v[1 : len(v)-1], rest, nil
 }
 
-func (p *parser) parseInlineTable(node *ast.Node, b []byte) ([]byte, error) {
+func (p *parser) parseInlineTable(b []byte) (ast.Reference, []byte, error) {
 	//inline-table = inline-table-open [ inline-table-keyvals ] inline-table-close
 	//inline-table-open  = %x7B ws     ; {
 	//inline-table-close = ws %x7D     ; }
 	//inline-table-sep   = ws %x2C ws  ; , Comma
 	//inline-table-keyvals = keyval [ inline-table-sep inline-table-keyvals ]
 
-	b = b[1:]
+	parent := p.builder.Push(ast.Node{
+		Kind: ast.InlineTable,
+	})
 
 	first := true
+	var child ast.Reference
+
+	b = b[1:]
+
 	var err error
 	for len(b) > 0 {
 		b = p.parseWhitespace(b)
@@ -261,24 +279,32 @@ func (p *parser) parseInlineTable(node *ast.Node, b []byte) ([]byte, error) {
 		if !first {
 			b, err = expect(',', b)
 			if err != nil {
-				return nil, err
+				return parent, nil, err
 			}
 			b = p.parseWhitespace(b)
 		}
-		var kv ast.Node
+		var kv ast.Reference
 		kv, b, err = p.parseKeyval(b)
 		if err != nil {
-			return nil, err
+			return parent, nil, err
 		}
-		node.Children = append(node.Children, kv)
+
+		if first {
+			p.builder.AttachChild(parent, kv)
+			first = false
+		} else {
+			p.builder.Chain(child, kv)
+		}
+		child = kv
 
 		first = false
 	}
 
-	return expect('}', b)
+	rest, err := expect('}', b)
+	return parent, rest, err
 }
 
-func (p *parser) parseValArray(node *ast.Node, b []byte) ([]byte, error) {
+func (p *parser) parseValArray(b []byte) (ast.Reference, []byte, error) {
 	//array = array-open [ array-values ] ws-comment-newline array-close
 	//array-open =  %x5B ; [
 	//array-close = %x5D ; ]
@@ -289,16 +315,22 @@ func (p *parser) parseValArray(node *ast.Node, b []byte) ([]byte, error) {
 
 	b = b[1:]
 
+	parent := p.builder.Push(ast.Node{
+		Kind: ast.Array,
+	})
+
 	first := true
+	var lastChild ast.Reference
+
 	var err error
 	for len(b) > 0 {
 		b, err = p.parseOptionalWhitespaceCommentNewline(b)
 		if err != nil {
-			return nil, err
+			return parent, nil, err
 		}
 
 		if len(b) == 0 {
-			return nil, unexpectedCharacter{b: b}
+			return parent, nil, unexpectedCharacter{b: b}
 		}
 
 		if b[0] == ']' {
@@ -306,29 +338,38 @@ func (p *parser) parseValArray(node *ast.Node, b []byte) ([]byte, error) {
 		}
 		if b[0] == ',' {
 			if first {
-				return nil, fmt.Errorf("array cannot start with comma")
+				return parent, nil, fmt.Errorf("array cannot start with comma")
 			}
 			b = b[1:]
 			b, err = p.parseOptionalWhitespaceCommentNewline(b)
 			if err != nil {
-				return nil, err
+				return parent, nil, err
 			}
 		}
 
-		var valueNode ast.Node
+		var valueRef ast.Reference
-		valueNode, b, err = p.parseVal(b)
+		valueRef, b, err = p.parseVal(b)
 		if err != nil {
-			return nil, err
+			return parent, nil, err
 		}
-		node.Children = append(node.Children, valueNode)
+
+		if first {
+			p.builder.AttachChild(parent, valueRef)
+			first = false
+		} else {
+			p.builder.Chain(lastChild, valueRef)
+		}
+		lastChild = valueRef
+
 		b, err = p.parseOptionalWhitespaceCommentNewline(b)
 		if err != nil {
-			return nil, err
+			return parent, nil, err
 		}
 		first = false
 	}
 
-	return expect(']', b)
+	rest, err := expect(']', b)
+	return parent, rest, err
 }
 
 func (p *parser) parseOptionalWhitespaceCommentNewline(b []byte) ([]byte, error) {
@@ -454,7 +495,7 @@ func (p *parser) parseMultilineBasicString(b []byte) ([]byte, []byte, error) {
 	return builder.Bytes(), rest, nil
 }
 
-func (p *parser) parseKey(b []byte) ([]ast.Node, []byte, error) {
+func (p *parser) parseKey(b []byte) (ast.Reference, []byte, error) {
 	//key = simple-key / dotted-key
 	//simple-key = quoted-key / unquoted-key
 	//
@@ -464,14 +505,12 @@ func (p *parser) parseKey(b []byte) ([]ast.Node, []byte, error) {
 	//
 	//dot-sep   = ws %x2E ws  ; . Period
 
-	var nodes []ast.Node
-
 	key, b, err := p.parseSimpleKey(b)
 	if err != nil {
-		return nodes, nil, err
+		return ast.Reference{}, nil, err
 	}
 
-	nodes = append(nodes, ast.Node{
+	ref := p.builder.Push(ast.Node{
 		Kind: ast.Key,
 		Data: key,
 	})
@@ -481,14 +520,14 @@ func (p *parser) parseKey(b []byte) ([]ast.Node, []byte, error) {
 		if len(b) > 0 && b[0] == '.' {
 			b, err = expect('.', b)
 			if err != nil {
-				return nodes, nil, err
+				return ref, nil, err
 			}
 			b = p.parseWhitespace(b)
 			key, b, err = p.parseSimpleKey(b)
 			if err != nil {
-				return nodes, nil, err
+				return ref, nil, err
 			}
-			nodes = append(nodes, ast.Node{
+			p.builder.PushAndChain(ast.Node{
 				Kind: ast.Key,
 				Data: key,
 			})
@@ -497,7 +536,7 @@ func (p *parser) parseKey(b []byte) ([]ast.Node, []byte, error) {
 		}
 	}
 
-	return nodes, b, nil
+	return ref, b, nil
 }
 
 func (p *parser) parseSimpleKey(b []byte) (key, rest []byte, err error) {
@@ -609,28 +648,30 @@ func (p *parser) parseWhitespace(b []byte) []byte {
 	return rest
 }
 
-func (p *parser) parseIntOrFloatOrDateTime(node *ast.Node, b []byte) ([]byte, error) {
+func (p *parser) parseIntOrFloatOrDateTime(b []byte) (ast.Reference, []byte, error) {
 	switch b[0] {
 	case 'i':
 		if !scanFollowsInf(b) {
-			return nil, fmt.Errorf("expected 'inf'")
+			return ast.Reference{}, nil, fmt.Errorf("expected 'inf'")
 		}
-		node.Kind = ast.Float
+		return p.builder.Push(ast.Node{
-		node.Data = b[:3]
+			Kind: ast.Float,
-		return b[3:], nil
+			Data: b[:3],
+		}), b[3:], nil
 	case 'n':
 		if !scanFollowsNan(b) {
-			return nil, fmt.Errorf("expected 'nan'")
+			return ast.Reference{}, nil, fmt.Errorf("expected 'nan'")
 		}
-		node.Kind = ast.Float
+		return p.builder.Push(ast.Node{
-		node.Data = b[:3]
+			Kind: ast.Float,
-		return b[3:], nil
+			Data: b[:3],
+		}), b[3:], nil
 	case '+', '-':
-		return p.scanIntOrFloat(node, b)
+		return p.scanIntOrFloat(b)
 	}
 
 	if len(b) < 3 {
-		return p.scanIntOrFloat(node, b)
+		return p.scanIntOrFloat(b)
 	}
 	s := 5
 	if len(b) < s {
@@ -641,10 +682,10 @@ func (p *parser) parseIntOrFloatOrDateTime(node *ast.Node, b []byte) ([]byte, er
 			continue
 		}
 		if idx == 2 && c == ':' || (idx == 4 && c == '-') {
-			return p.scanDateTime(node, b)
+			return p.scanDateTime(b)
 		}
 	}
-	return p.scanIntOrFloat(node, b)
+	return p.scanIntOrFloat(b)
 }
 
 func digitsToInt(b []byte) int {
@@ -656,7 +697,7 @@ func digitsToInt(b []byte) int {
 	return x
 }
 
-func (p *parser) scanDateTime(node *ast.Node, b []byte) ([]byte, error) {
+func (p *parser) scanDateTime(b []byte) (ast.Reference, []byte, error) {
 	// scans for contiguous characters in [0-9T:Z.+-], and up to one space if
 	// followed by a digit.
 
@@ -686,22 +727,25 @@ func (p *parser) scanDateTime(node *ast.Node, b []byte) ([]byte, error) {
 		}
 	}
 
+	var kind ast.Kind
+
 	if hasTime {
 		if hasTz {
-			node.Kind = ast.DateTime
+			kind = ast.DateTime
 		} else {
-			node.Kind = ast.LocalDateTime
+			kind = ast.LocalDateTime
 		}
 	} else {
 		if hasTz {
-			return nil, fmt.Errorf("possible DateTime cannot have a timezone but no time component")
+			return ast.Reference{}, nil, fmt.Errorf("possible DateTime cannot have a timezone but no time component")
 		}
-		node.Kind = ast.LocalDate
+		kind = ast.LocalDate
 	}
 
-	node.Data = b[:i]
+	return p.builder.Push(ast.Node{
-
+		Kind: kind,
-	return b[i:], nil
+		Data: b[:i],
+	}), b[i:], nil
 }
 
 func (p *parser) parseDateTime(b []byte) ([]byte, error) {
@@ -964,7 +1008,7 @@ func (p *parser) parseTime(b []byte) ([]byte, error) {
 	return b[idx:], nil
 }
 
-func (p *parser) scanIntOrFloat(node *ast.Node, b []byte) ([]byte, error) {
+func (p *parser) scanIntOrFloat(b []byte) (ast.Reference, []byte, error) {
 	i := 0
 
 	if len(b) > 2 && b[0] == '0' {
@@ -989,9 +1033,10 @@ func (p *parser) scanIntOrFloat(node *ast.Node, b []byte) ([]byte, error) {
 			}
 		}
 
-		node.Kind = ast.Integer
+		return p.builder.Push(ast.Node{
-		node.Data = b[:i]
+			Kind: ast.Integer,
-		return b[i:], nil
+			Data: b[:i],
+		}), b[i:], nil
 	}
 
 	isFloat := false
@@ -1010,31 +1055,36 @@ func (p *parser) scanIntOrFloat(node *ast.Node, b []byte) ([]byte, error) {
 
 		if c == 'i' {
 			if scanFollowsInf(b[i:]) {
-				node.Kind = ast.Float
+				return p.builder.Push(ast.Node{
-				node.Data = b[:i+3]
+					Kind: ast.Float,
-				return b[i+3:], nil
+					Data: b[:i+3],
+				}), b[i+3:], nil
 			}
-			return nil, fmt.Errorf("unexpected character i while scanning for a number")
+			return ast.Reference{}, nil, fmt.Errorf("unexpected character i while scanning for a number")
 		}
 		if c == 'n' {
 			if scanFollowsNan(b[i:]) {
-				node.Kind = ast.Float
+				return p.builder.Push(ast.Node{
-				node.Data = b[:i+3]
+					Kind: ast.Float,
-				return b[i+3:], nil
+					Data: b[:i+3],
+				}), b[i+3:], nil
 			}
-			return nil, fmt.Errorf("unexpected character n while scanning for a number")
+			return ast.Reference{}, nil, fmt.Errorf("unexpected character n while scanning for a number")
 		}
 
 		break
 	}
 
+	kind := ast.Integer
+
 	if isFloat {
-		node.Kind = ast.Float
+		kind = ast.Float
-	} else {
-		node.Kind = ast.Integer
 	}
-	node.Data = b[:i]
+
-	return b[i:], nil
+	return p.builder.Push(ast.Node{
+		Kind: kind,
+		Data: b[:i],
+	}), b[i:], nil
 }
 
 func isDigit(r byte) bool {

parser_test.go

@@ -125,44 +125,128 @@ func TestParser_AST_Numbers(t *testing.T) {
 			} else {
 				require.NoError(t, err)
 
-				expected := ast.Root{
+				expected := astRoot{
-					ast.Node{
+					astNode{
 						Kind: ast.KeyValue,
-						Children: []ast.Node{
+						Children: []astNode{
-							{Kind: ast.Key, Data: []byte(`A`)},
 							{Kind: e.kind, Data: []byte(e.input)},
+							{Kind: ast.Key, Data: []byte(`A`)},
 						},
 					},
 				}
 
-				require.Equal(t, expected, p.tree)
+				compareAST(t, expected, p.builder.Finish())
 			}
 		})
 	}
 }
 
+type astRoot []astNode
+type astNode struct {
+	Kind     ast.Kind
+	Data     []byte
+	Children []astNode
+}
+
+func compareAST(t *testing.T, expected astRoot, actual *ast.Root) {
+	it := actual.Iterator()
+	compareIterator(t, expected, it)
+}
+
+func compareIterator(t *testing.T, expected []astNode, actual ast.Iterator) {
+	idx := 0
+
+	for actual.Next() {
+		n := actual.Node()
+
+		if idx >= len(expected) {
+			t.Fatal("extra child in actual tree")
+		}
+		e := expected[idx]
+
+		require.Equal(t, e.Kind, n.Kind)
+		require.Equal(t, e.Data, n.Data)
+
+		compareIterator(t, e.Children, n.Children())
+
+		idx++
+	}
+
+	if idx < len(expected) {
+		t.Fatal("missing children in actual", "idx =", idx, "expected =", len(expected))
+	}
+}
+
+func (r astRoot) toOrig() *ast.Root {
+	builder := &ast.Builder{}
+
+	var last ast.Reference
+
+	for i, n := range r {
+		ref := builder.Push(ast.Node{
+			Kind: n.Kind,
+			Data: n.Data,
+		})
+
+		if i > 0 {
+			builder.Chain(last, ref)
+		}
+		last = ref
+
+		if len(n.Children) > 0 {
+			c := childrenToOrig(builder, n.Children)
+			builder.AttachChild(ref, c)
+		}
+	}
+
+	return builder.Finish()
+}
+
+func childrenToOrig(b *ast.Builder, nodes []astNode) ast.Reference {
+	var first ast.Reference
+	var last ast.Reference
+	for i, n := range nodes {
+		ref := b.Push(ast.Node{
+			Kind: n.Kind,
+			Data: n.Data,
+		})
+		if i == 0 {
+			first = ref
+		} else {
+			b.Chain(last, ref)
+		}
+		last = ref
+
+		if len(n.Children) > 0 {
+			c := childrenToOrig(b, n.Children)
+			b.AttachChild(ref, c)
+		}
+	}
+	return first
+}
+
 func TestParser_AST(t *testing.T) {
 	examples := []struct {
 		desc  string
 		input string
-		ast   ast.Root
+		ast   astRoot
 		err   bool
 	}{
 		{
 			desc:  "simple string assignment",
 			input: `A = "hello"`,
-			ast: ast.Root{
+			ast: astRoot{
-				ast.Node{
+				astNode{
 					Kind: ast.KeyValue,
-					Children: []ast.Node{
+					Children: []astNode{
-						{
-							Kind: ast.Key,
-							Data: []byte(`A`),
-						},
 						{
 							Kind: ast.String,
 							Data: []byte(`hello`),
 						},
+						{
+							Kind: ast.Key,
+							Data: []byte(`A`),
+						},
 					},
 				},
 			},
@@ -170,18 +254,18 @@ func TestParser_AST(t *testing.T) {
 		{
 			desc:  "simple bool assignment",
 			input: `A = true`,
-			ast: ast.Root{
+			ast: astRoot{
-				ast.Node{
+				astNode{
 					Kind: ast.KeyValue,
-					Children: []ast.Node{
+					Children: []astNode{
-						{
-							Kind: ast.Key,
-							Data: []byte(`A`),
-						},
 						{
 							Kind: ast.Bool,
 							Data: []byte(`true`),
 						},
+						{
+							Kind: ast.Key,
+							Data: []byte(`A`),
+						},
 					},
 				},
 			},
@@ -189,24 +273,20 @@ func TestParser_AST(t *testing.T) {
 		{
 			desc:  "array of strings",
 			input: `A = ["hello", ["world", "again"]]`,
-			ast: ast.Root{
+			ast: astRoot{
-				ast.Node{
+				astNode{
 					Kind: ast.KeyValue,
-					Children: []ast.Node{
+					Children: []astNode{
-						{
-							Kind: ast.Key,
-							Data: []byte(`A`),
-						},
 						{
 							Kind: ast.Array,
-							Children: []ast.Node{
+							Children: []astNode{
 								{
 									Kind: ast.String,
 									Data: []byte(`hello`),
 								},
 								{
 									Kind: ast.Array,
-									Children: []ast.Node{
+									Children: []astNode{
 										{
 											Kind: ast.String,
 											Data: []byte(`world`),
@@ -219,6 +299,10 @@ func TestParser_AST(t *testing.T) {
 								},
 							},
 						},
+						{
+							Kind: ast.Key,
+							Data: []byte(`A`),
+						},
 					},
 				},
 			},
@@ -226,17 +310,13 @@ func TestParser_AST(t *testing.T) {
 		{
 			desc:  "array of arrays of strings",
 			input: `A = ["hello", "world"]`,
-			ast: ast.Root{
+			ast: astRoot{
-				ast.Node{
+				astNode{
 					Kind: ast.KeyValue,
-					Children: []ast.Node{
+					Children: []astNode{
-						{
-							Kind: ast.Key,
-							Data: []byte(`A`),
-						},
 						{
 							Kind: ast.Array,
-							Children: []ast.Node{
+							Children: []astNode{
 								{
 									Kind: ast.String,
 									Data: []byte(`hello`),
@@ -247,6 +327,10 @@ func TestParser_AST(t *testing.T) {
 								},
 							},
 						},
+						{
+							Kind: ast.Key,
+							Data: []byte(`A`),
+						},
 					},
 				},
 			},
@@ -254,33 +338,33 @@ func TestParser_AST(t *testing.T) {
 		{
 			desc:  "inline table",
 			input: `name = { first = "Tom", last = "Preston-Werner" }`,
-			ast: ast.Root{
+			ast: astRoot{
-				ast.Node{
+				astNode{
 					Kind: ast.KeyValue,
-					Children: []ast.Node{
+					Children: []astNode{
-						{
-							Kind: ast.Key,
-							Data: []byte(`name`),
-						},
 						{
 							Kind: ast.InlineTable,
-							Children: []ast.Node{
+							Children: []astNode{
 								{
 									Kind: ast.KeyValue,
-									Children: []ast.Node{
+									Children: []astNode{
-										{Kind: ast.Key, Data: []byte(`first`)},
 										{Kind: ast.String, Data: []byte(`Tom`)},
+										{Kind: ast.Key, Data: []byte(`first`)},
 									},
 								},
 								{
 									Kind: ast.KeyValue,
-									Children: []ast.Node{
+									Children: []astNode{
-										{Kind: ast.Key, Data: []byte(`last`)},
 										{Kind: ast.String, Data: []byte(`Preston-Werner`)},
+										{Kind: ast.Key, Data: []byte(`last`)},
 									},
 								},
 							},
 						},
+						{
+							Kind: ast.Key,
+							Data: []byte(`name`),
+						},
 					},
 				},
 			},
@@ -295,7 +379,7 @@ func TestParser_AST(t *testing.T) {
 				require.Error(t, err)
 			} else {
 				require.NoError(t, err)
-				require.Equal(t, e.ast, p.tree)
+				compareAST(t, e.ast, p.builder.Finish())
 			}
 		})
 	}

unmarshaler.go

@@ -17,7 +17,7 @@ func Unmarshal(data []byte, v interface{}) error {
 	}
 
 	d := decoder{}
-	return d.fromAst(p.tree, v)
+	return d.fromAst(p.builder.Finish(), v)
 }
 
 type decoder struct {
@@ -41,7 +41,7 @@ func (d *decoder) arrayIndex(append bool, v reflect.Value) int {
 	return idx
 }
 
-func (d *decoder) fromAst(tree ast.Root, v interface{}) error {
+func (d *decoder) fromAst(tree *ast.Root, v interface{}) error {
 	r := reflect.ValueOf(v)
 	if r.Kind() != reflect.Ptr {
 		return fmt.Errorf("need to target a pointer, not %s", r.Kind())
@@ -54,14 +54,17 @@ func (d *decoder) fromAst(tree ast.Root, v interface{}) error {
 	var skipUntilTable bool
 	var root target = valueTarget(r.Elem())
 	current := root
-	for _, node := range tree {
+
+	it := tree.Iterator()
+	for it.Next() {
+		node := it.Node()
 		var found bool
 		switch node.Kind {
 		case ast.KeyValue:
 			if skipUntilTable {
 				continue
 			}
-			err = d.unmarshalKeyValue(current, &node)
+			err = d.unmarshalKeyValue(current, node)
 			found = true
 		case ast.Table:
 			current, found, err = d.scopeWithKey(root, node.Key())
@@ -91,10 +94,12 @@ func (d *decoder) fromAst(tree ast.Root, v interface{}) error {
 //
 // When encountering slices, it should always use its last element, and error
 // if the slice does not have any.
-func (d *decoder) scopeWithKey(x target, key []ast.Node) (target, bool, error) {
+func (d *decoder) scopeWithKey(x target, key ast.Iterator) (target, bool, error) {
 	var err error
 	found := true
-	for _, n := range key {
+
+	for key.Next() {
+		n := key.Node()
 		x, found, err = d.scopeTableTarget(false, x, string(n.Data))
 		if err != nil || !found {
 			return nil, found, err
@@ -108,18 +113,21 @@ func (d *decoder) scopeWithKey(x target, key []ast.Node) (target, bool, error) {
 //
 // It is the same as scopeWithKey, but when scoping the last part of the key
 // it creates a new element in the array instead of using the last one.
-func (d *decoder) scopeWithArrayTable(x target, key []ast.Node) (target, bool, error) {
+func (d *decoder) scopeWithArrayTable(x target, key ast.Iterator) (target, bool, error) {
 	var err error
 	found := true
-	if len(key) > 1 {
+	for key.Next() {
-		for _, n := range key[:len(key)-1] {
+		n := key.Node()
-			x, found, err = d.scopeTableTarget(false, x, string(n.Data))
+		if !n.Next().Valid() { // want to stop at one before last
-			if err != nil || !found {
+			break
-				return nil, found, err
+		}
-			}
+		x, found, err = d.scopeTableTarget(false, x, string(n.Data))
+		if err != nil || !found {
+			return nil, found, err
 		}
 	}
-	x, found, err = d.scopeTableTarget(false, x, string(key[len(key)-1].Data))
+	n := key.Node()
+	x, found, err = d.scopeTableTarget(false, x, string(n.Data))
 	if err != nil || !found {
 		return x, found, err
 	}
@@ -152,7 +160,7 @@ func (d *decoder) scopeWithArrayTable(x target, key []ast.Node) (target, bool, e
 	return x, found, err
 }
 
-func (d *decoder) unmarshalKeyValue(x target, node *ast.Node) error {
+func (d *decoder) unmarshalKeyValue(x target, node ast.Node) error {
 	assertNode(ast.KeyValue, node)
 
 	x, found, err := d.scopeWithKey(x, node.Key())
@@ -170,7 +178,7 @@ func (d *decoder) unmarshalKeyValue(x target, node *ast.Node) error {
 
 var textUnmarshalerType = reflect.TypeOf(new(encoding.TextUnmarshaler)).Elem()
 
-func tryTextUnmarshaler(x target, node *ast.Node) (bool, error) {
+func tryTextUnmarshaler(x target, node ast.Node) (bool, error) {
 	v := x.get()
 
 	if v.Kind() != reflect.Struct {
@@ -185,7 +193,7 @@ func tryTextUnmarshaler(x target, node *ast.Node) (bool, error) {
 	return false, nil
 }
 
-func (d *decoder) unmarshalValue(x target, node *ast.Node) error {
+func (d *decoder) unmarshalValue(x target, node ast.Node) error {
 	v := x.get()
 	if v.Kind() == reflect.Ptr {
 		if !v.Elem().IsValid() {
@@ -225,7 +233,7 @@ func (d *decoder) unmarshalValue(x target, node *ast.Node) error {
 	}
 }
 
-func unmarshalLocalDateTime(x target, node *ast.Node) error {
+func unmarshalLocalDateTime(x target, node ast.Node) error {
 	assertNode(ast.LocalDateTime, node)
 	v, rest, err := parseLocalDateTime(node.Data)
 	if err != nil {
@@ -237,7 +245,7 @@ func unmarshalLocalDateTime(x target, node *ast.Node) error {
 	return setLocalDateTime(x, v)
 }
 
-func unmarshalDateTime(x target, node *ast.Node) error {
+func unmarshalDateTime(x target, node ast.Node) error {
 	assertNode(ast.DateTime, node)
 	v, err := parseDateTime(node.Data)
 	if err != nil {
@@ -254,18 +262,18 @@ func setDateTime(x target, v time.Time) error {
 	return x.set(reflect.ValueOf(v))
 }
 
-func unmarshalString(x target, node *ast.Node) error {
+func unmarshalString(x target, node ast.Node) error {
 	assertNode(ast.String, node)
 	return setString(x, string(node.Data))
 }
 
-func unmarshalBool(x target, node *ast.Node) error {
+func unmarshalBool(x target, node ast.Node) error {
 	assertNode(ast.Bool, node)
 	v := node.Data[0] == 't'
 	return setBool(x, v)
 }
 
-func unmarshalInteger(x target, node *ast.Node) error {
+func unmarshalInteger(x target, node ast.Node) error {
 	assertNode(ast.Integer, node)
 	v, err := parseInteger(node.Data)
 	if err != nil {
@@ -274,7 +282,7 @@ func unmarshalInteger(x target, node *ast.Node) error {
 	return setInt64(x, v)
 }
 
-func unmarshalFloat(x target, node *ast.Node) error {
+func unmarshalFloat(x target, node ast.Node) error {
 	assertNode(ast.Float, node)
 	v, err := parseFloat(node.Data)
 	if err != nil {
@@ -283,11 +291,13 @@ func unmarshalFloat(x target, node *ast.Node) error {
 	return setFloat64(x, v)
 }
 
-func (d *decoder) unmarshalInlineTable(x target, node *ast.Node) error {
+func (d *decoder) unmarshalInlineTable(x target, node ast.Node) error {
 	assertNode(ast.InlineTable, node)
 
-	for _, kv := range node.Children {
+	it := node.Children()
-		err := d.unmarshalKeyValue(x, &kv)
+	for it.Next() {
+		n := it.Node()
+		err := d.unmarshalKeyValue(x, n)
 		if err != nil {
 			return err
 		}
@@ -295,7 +305,7 @@ func (d *decoder) unmarshalInlineTable(x target, node *ast.Node) error {
 	return nil
 }
 
-func (d *decoder) unmarshalArray(x target, node *ast.Node) error {
+func (d *decoder) unmarshalArray(x target, node ast.Node) error {
 	assertNode(ast.Array, node)
 
 	err := ensureValueIndexable(x)
@@ -303,7 +313,10 @@ func (d *decoder) unmarshalArray(x target, node *ast.Node) error {
 		return err
 	}
 
-	for idx, n := range node.Children {
+	it := node.Children()
+	idx := 0
+	for it.Next() {
+		n := it.Node()
 		v, err := elementAt(x, idx)
 		if err != nil {
 			return err
@@ -313,15 +326,16 @@ func (d *decoder) unmarshalArray(x target, node *ast.Node) error {
 			// mimic encoding/json
 			break
 		}
-		err = d.unmarshalValue(v, &n)
+		err = d.unmarshalValue(v, n)
 		if err != nil {
 			return err
 		}
+		idx++
 	}
 	return nil
 }
 
-func assertNode(expected ast.Kind, node *ast.Node) {
+func assertNode(expected ast.Kind, node ast.Node) {
 	if node.Kind != expected {
 		panic(fmt.Errorf("expected node of kind %s, not %s", expected, node.Kind))
 	}

unmarshaler_test.go

@@ -660,18 +660,18 @@ B = "data"`,
 }
 
 func TestFromAst_KV(t *testing.T) {
-	root := ast.Root{
+	root := astRoot{
-		ast.Node{
+		astNode{
 			Kind: ast.KeyValue,
-			Children: []ast.Node{
+			Children: []astNode{
-				{
-					Kind: ast.Key,
-					Data: []byte(`Foo`),
-				},
 				{
 					Kind: ast.String,
 					Data: []byte(`hello`),
 				},
+				{
+					Kind: ast.Key,
+					Data: []byte(`Foo`),
+				},
 			},
 		},
 	}
@@ -682,44 +682,44 @@ func TestFromAst_KV(t *testing.T) {
 
 	x := Doc{}
 	d := decoder{}
-	err := d.fromAst(root, &x)
+	err := d.fromAst(root.toOrig(), &x)
 	require.NoError(t, err)
 	assert.Equal(t, Doc{Foo: "hello"}, x)
 }
 
 func TestFromAst_Table(t *testing.T) {
 	t.Run("one level table on struct", func(t *testing.T) {
-		root := ast.Root{
+		root := astRoot{
-			ast.Node{
+			astNode{
 				Kind: ast.Table,
-				Children: []ast.Node{
+				Children: []astNode{
 					{Kind: ast.Key, Data: []byte(`Level1`)},
 				},
 			},
-			ast.Node{
+			astNode{
 				Kind: ast.KeyValue,
-				Children: []ast.Node{
+				Children: []astNode{
-					{
-						Kind: ast.Key,
-						Data: []byte(`A`),
-					},
 					{
 						Kind: ast.String,
 						Data: []byte(`hello`),
 					},
-				},
-			},
-			ast.Node{
-				Kind: ast.KeyValue,
-				Children: []ast.Node{
 					{
 						Kind: ast.Key,
-						Data: []byte(`B`),
+						Data: []byte(`A`),
 					},
+				},
+			},
+			astNode{
+				Kind: ast.KeyValue,
+				Children: []astNode{
 					{
 						Kind: ast.String,
 						Data: []byte(`world`),
 					},
+					{
+						Kind: ast.Key,
+						Data: []byte(`B`),
+					},
 				},
 			},
 		}
@@ -735,7 +735,7 @@ func TestFromAst_Table(t *testing.T) {
 
 		x := Doc{}
 		d := decoder{}
-		err := d.fromAst(root, &x)
+		err := d.fromAst(root.toOrig(), &x)
 		require.NoError(t, err)
 		assert.Equal(t, Doc{
 			Level1: Level1{
@@ -745,25 +745,25 @@ func TestFromAst_Table(t *testing.T) {
 		}, x)
 	})
 	t.Run("one level table on struct", func(t *testing.T) {
-		root := ast.Root{
+		root := astRoot{
-			ast.Node{
+			astNode{
 				Kind: ast.Table,
-				Children: []ast.Node{
+				Children: []astNode{
 					{Kind: ast.Key, Data: []byte(`A`)},
 					{Kind: ast.Key, Data: []byte(`B`)},
 				},
 			},
-			ast.Node{
+			astNode{
 				Kind: ast.KeyValue,
-				Children: []ast.Node{
+				Children: []astNode{
-					{
-						Kind: ast.Key,
-						Data: []byte(`C`),
-					},
 					{
 						Kind: ast.String,
 						Data: []byte(`value`),
 					},
+					{
+						Kind: ast.Key,
+						Data: []byte(`C`),
+					},
 				},
 			},
 		}
@@ -782,7 +782,7 @@ func TestFromAst_Table(t *testing.T) {
 
 		x := Doc{}
 		d := decoder{}
-		err := d.fromAst(root, &x)
+		err := d.fromAst(root.toOrig(), &x)
 		require.NoError(t, err)
 		assert.Equal(t, Doc{
 			A: A{B: B{C: "value"}},
@@ -792,32 +792,33 @@ func TestFromAst_Table(t *testing.T) {
 
 func TestFromAst_InlineTable(t *testing.T) {
 	t.Run("one level of strings", func(t *testing.T) {
-		root := ast.Root{
+		root := astRoot{
-			ast.Node{
+			astNode{
 				Kind: ast.KeyValue,
-				Children: []ast.Node{
+				Children: []astNode{
-					{
-						Kind: ast.Key,
-						Data: []byte(`Name`)},
 					{
 						Kind: ast.InlineTable,
-						Children: []ast.Node{
+						Children: []astNode{
 							{
 								Kind: ast.KeyValue,
-								Children: []ast.Node{
+								Children: []astNode{
-									{Kind: ast.Key, Data: []byte(`First`)},
 									{Kind: ast.String, Data: []byte(`Tom`)},
+									{Kind: ast.Key, Data: []byte(`First`)},
 								},
 							},
 							{
 								Kind: ast.KeyValue,
-								Children: []ast.Node{
+								Children: []astNode{
-									{Kind: ast.Key, Data: []byte(`Last`)},
 									{Kind: ast.String, Data: []byte(`Preston-Werner`)},
+									{Kind: ast.Key, Data: []byte(`Last`)},
 								},
 							},
 						},
 					},
+					{
+						Kind: ast.Key,
+						Data: []byte(`Name`),
+					},
 				},
 			},
 		}
@@ -833,7 +834,7 @@ func TestFromAst_InlineTable(t *testing.T) {
 
 		x := Doc{}
 		d := decoder{}
-		err := d.fromAst(root, &x)
+		err := d.fromAst(root.toOrig(), &x)
 		require.NoError(t, err)
 		assert.Equal(t, Doc{
 			Name: Name{
@@ -847,17 +848,13 @@ func TestFromAst_InlineTable(t *testing.T) {
 
 func TestFromAst_Slice(t *testing.T) {
 	t.Run("slice of string", func(t *testing.T) {
-		root := ast.Root{
+		root := astRoot{
-			ast.Node{
+			astNode{
 				Kind: ast.KeyValue,
-				Children: []ast.Node{
+				Children: []astNode{
-					{
-						Kind: ast.Key,
-						Data: []byte(`Foo`),
-					},
 					{
 						Kind: ast.Array,
-						Children: []ast.Node{
+						Children: []astNode{
 							{
 								Kind: ast.String,
 								Data: []byte(`hello`),
@@ -868,6 +865,10 @@ func TestFromAst_Slice(t *testing.T) {
 							},
 						},
 					},
+					{
+						Kind: ast.Key,
+						Data: []byte(`Foo`),
+					},
 				},
 			},
 		}
@@ -878,23 +879,19 @@ func TestFromAst_Slice(t *testing.T) {
 
 		x := Doc{}
 		d := decoder{}
-		err := d.fromAst(root, &x)
+		err := d.fromAst(root.toOrig(), &x)
 		require.NoError(t, err)
 		assert.Equal(t, Doc{Foo: []string{"hello", "world"}}, x)
 	})
 
 	t.Run("slice of interfaces for strings", func(t *testing.T) {
-		root := ast.Root{
+		root := astRoot{
-			ast.Node{
+			astNode{
 				Kind: ast.KeyValue,
-				Children: []ast.Node{
+				Children: []astNode{
-					{
-						Kind: ast.Key,
-						Data: []byte(`Foo`),
-					},
 					{
 						Kind: ast.Array,
-						Children: []ast.Node{
+						Children: []astNode{
 							{
 								Kind: ast.String,
 								Data: []byte(`hello`),
@@ -905,6 +902,10 @@ func TestFromAst_Slice(t *testing.T) {
 							},
 						},
 					},
+					{
+						Kind: ast.Key,
+						Data: []byte(`Foo`),
+					},
 				},
 			},
 		}
@@ -915,30 +916,26 @@ func TestFromAst_Slice(t *testing.T) {
 
 		x := Doc{}
 		d := decoder{}
-		err := d.fromAst(root, &x)
+		err := d.fromAst(root.toOrig(), &x)
 		require.NoError(t, err)
 		assert.Equal(t, Doc{Foo: []interface{}{"hello", "world"}}, x)
 	})
 
 	t.Run("slice of interfaces with slices", func(t *testing.T) {
-		root := ast.Root{
+		root := astRoot{
-			ast.Node{
+			astNode{
 				Kind: ast.KeyValue,
-				Children: []ast.Node{
+				Children: []astNode{
-					{
-						Kind: ast.Key,
-						Data: []byte(`Foo`),
-					},
 					{
 						Kind: ast.Array,
-						Children: []ast.Node{
+						Children: []astNode{
 							{
 								Kind: ast.String,
 								Data: []byte(`hello`),
 							},
 							{
 								Kind: ast.Array,
-								Children: []ast.Node{
+								Children: []astNode{
 									{
 										Kind: ast.String,
 										Data: []byte(`inner1`),
@@ -951,6 +948,10 @@ func TestFromAst_Slice(t *testing.T) {
 							},
 						},
 					},
+					{
+						Kind: ast.Key,
+						Data: []byte(`Foo`),
+					},
 				},
 			},
 		}
@@ -961,7 +962,7 @@ func TestFromAst_Slice(t *testing.T) {
 
 		x := Doc{}
 		d := decoder{}
-		err := d.fromAst(root, &x)
+		err := d.fromAst(root.toOrig(), &x)
 		require.NoError(t, err)
 		assert.Equal(t, Doc{Foo: []interface{}{"hello", []interface{}{"inner1", "inner2"}}}, x)
 	})