let data1 = "aaab"
let data2 = "aaaba"
let data3 = "bbba"
let pattern = /a+b/

let b1 = try! pattern.firstMatch(in: data1) != nil
//b1 is true
let b2 = try! pattern.firstMatch(in: data2) != nil
//b2 is true
let b3 = try! pattern.firstMatch(in: data3) != nil
//b3 is false

print("b1 is \(b1)")
print("b2 is \(b2)")
print("b3 is \(b3)")