func (p Position) String() string {
	if !p.IsValid() {
		return "-"
	}
	var s string
	if p.Filename != "" {
		s += p.Filename + ":"
	}
	s += strconv.Itoa(p.Line)
	return s
}
String represents Position as a string.
package src
import (
	"os"
	"path/filepath"
	"runtime"
	"strconv"
)
type Position struct {
	Filename string
	Line     int  
}
func FramePosition(f runtime.Frame) Position {
	return Position{
		Filename: f.File,
		Line:     f.Line,
	}
}
func (p Position) IsValid() bool {
	return p.Line > 0
}