Golang github.com-albrow-calc-token.Buffer类(方法)实例源码

func newUnexpectedTokenErrorNext(buf *token.Buffer) error {
	t, err := buf.Read()
	if err != nil {
		return err
	}
	return newUnexpectedTokenError(t)
}

// 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)
	}
}

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)
}

// 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
}