1. interface searchFunc{
    2.     (source:string,substr?:string):boolean
    3. }
    6. let sf:searchFunc = function(sr:string,sb?:string){
    7.     return sr.length > (sb?.length || 0)
    8. }
    11. let sf2:searchFunc = function(sr:string,sb?:string):boolean{
    12.     return sr.length > (sb?.length || 0)
    13. }