// 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
}
func Eval(tree ast.Node) (*big.Rat, error) {
switch node := tree.(type) {
case *ast.Number:
return parseNumNode(node)
case *ast.BaseNode:
return evalNodes(tree.Children())
default:
return nil, fmt.Errorf("Unkown node type: %T", tree)
}
}
// 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
}
// 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
}