1 package ast

     2 

     3 type Reference int

     4 

     5 const InvalidReference Reference = -1

     6 

     7 func (r Reference) Valid() bool {

     8 	return r != InvalidReference

     9 }

    10 

    11 type Builder struct {

    12 	tree    Root

    13 	lastIdx int

    14 }

    15 

    16 func (b *Builder) Tree() *Root {

    17 	return &b.tree

    18 }

    19 

    20 func (b *Builder) NodeAt(ref Reference) *Node {

    21 	return b.tree.at(ref)

    22 }

    23 

    24 func (b *Builder) Reset() {

    25 	b.tree.nodes = b.tree.nodes[:0]

    26 	b.lastIdx = 0

    27 }

    28 

    29 func (b *Builder) Push(n Node) Reference {

    30 	b.lastIdx = len(b.tree.nodes)

    31 	b.tree.nodes = append(b.tree.nodes, n)

    32 	return Reference(b.lastIdx)

    33 }

    34 

    35 func (b *Builder) PushAndChain(n Node) Reference {

    36 	newIdx := len(b.tree.nodes)

    37 	b.tree.nodes = append(b.tree.nodes, n)

    38 	if b.lastIdx >= 0 {

    39 		b.tree.nodes[b.lastIdx].next = newIdx - b.lastIdx

    40 	}

    41 	b.lastIdx = newIdx

    42 	return Reference(b.lastIdx)

    43 }

    44 

    45 func (b *Builder) AttachChild(parent Reference, child Reference) {

    46 	b.tree.nodes[parent].child = int(child) - int(parent)

    47 }

    48 

    49 func (b *Builder) Chain(from Reference, to Reference) {

    50 	b.tree.nodes[from].next = int(to) - int(from)

    51 }