// E'1 -> Number
func ep1(buf *token.Buffer, tree ast.Node) (newTree ast.Node, err error) {
origPos := buf.Pos()
defer func() {
if err != nil {
buf.MustSeek(origPos)
}
}()
node, err := termNumber(buf)
if err != nil {
return nil, err
}
newTree = tree.Copy()
newTree.AddChild(node)
return newTree, nil
}
// E' -> Number | "(" E ")"
func ep(buf *token.Buffer, tree ast.Node) (newTree ast.Node, err error) {
origPos := buf.Pos()
defer func() {
if err != nil {
buf.MustSeek(origPos)
}
}()
if newTree, err := ep1(buf, tree); err == nil {
return newTree, nil
} else if newTree, err := ep2(buf, tree); err == nil {
return newTree, nil
}
buf.MustSeek(origPos)
return nil, newUnexpectedTokenErrorNext(buf)
}
func termNumber(buf *token.Buffer) (node ast.Node, err error) {
origPos := buf.Pos()
defer func() {
if err != nil {
buf.MustSeek(origPos)
}
}()
if t, err := buf.Read(); err != nil {
return nil, err
} else if t.Class == token.Number {
return &ast.Number{
Value: t.Value,
}, nil
} else {
return nil, newUnexpectedTokenError(t)
}
}
// E'2 -> "(" E ")"
func ep2(buf *token.Buffer, tree ast.Node) (newTree ast.Node, err error) {
origPos := buf.Pos()
defer func() {
if err != nil {
buf.MustSeek(origPos)
}
}()
newTree = tree.Copy()
expr := ast.New()
newTree.AddChild(expr)
if err := termOpenParen(buf); err != nil {
return nil, err
}
if buf.Pos() >= buf.Len() {
return nil, io.EOF
}
eTree, err := e(buf, tree.Copy())
if err != nil {
return nil, err
}
expr.AddChildren(eTree.Children())
if buf.Pos() >= buf.Len() {
return nil, io.EOF
}
if err := termCloseParen(buf); err != nil {
return nil, err
}
return newTree, nil
}
// E1 -> E' Op E
func e1(buf *token.Buffer, tree ast.Node) (newTree ast.Node, err error) {
origPos := buf.Pos()
defer func() {
if err != nil {
buf.MustSeek(origPos)
}
}()
newTree = tree.Copy()
epTree, err := ep(buf, tree.Copy())
if err != nil {
return nil, err
}
newTree.AddChildren(epTree.Children())
if buf.Pos() >= buf.Len() {
return nil, io.EOF
}
opNode, err := termOp(buf)
if err != nil {
return nil, err
}
newTree.AddChild(opNode)
if buf.Pos() >= buf.Len() {
return nil, io.EOF
}
eTree, err := e(buf, tree.Copy())
if err != nil {
return nil, err
}
newTree.AddChildren(eTree.Children())
return newTree, nil
}
func termOp(buf *token.Buffer) (node ast.Node, err error) {
origPos := buf.Pos()
defer func() {
if err != nil {
buf.MustSeek(origPos)
}
}()
t, err := buf.Read()
if err != nil {
return nil, err
}
switch t.Class {
case token.Add:
return &ast.Operator{
Class: ast.OpAdd,
}, nil
case token.Subtract:
return &ast.Operator{
Class: ast.OpSubtract,
}, nil
}
return nil, newUnexpectedTokenError(t)
}