func ExpandFilename(s string, u *user.User) (string, error) {
	if strings.HasPrefix(s, "~/") {
		if u == nil {
			var err error
			u, err = user.Current()
			if err != nil {
				return "", err
			}
		}
		s = u.HomeDir + s[1:]
	}
	return s, nil
}
ExpandFilename replace '~/' with the user home directory.
package interative
import (
	"fmt"
	"io"
	"log"
	"os"
	"os/user"
	"strings"
	"github.com/chzyer/readline"
	"github.com/rumlang/rum/parser"
	rumRuntime "github.com/rumlang/rum/runtime"
)
const (
	defaultPrompt = ">>> "
)