let testString = """
The cat
sat on
the mat
"""

public struct RegularExpression: ExpressibleByStringLiteral {
    public let pattern: String
    private let regularExpression: NSRegularExpression

    init(_ pattern: String) {
        self.pattern = pattern
        do {
            self.regularExpression = try NSRegularExpression(pattern: pattern)
        } catch {
            preconditionFailure("Illegal regular expression pattern: \(pattern).")
        }
    }

    public init(stringLiteral value: String) {
        self.init(value)

    }

    public func matches(_ string: String) -> Bool {
        return self.regularExpression.firstMatch(in: string, options: [], range: NSRange(string.startIndex..., in: string)) != nil
    }
}


let regularExpression: RegularExpression = "the"
regularExpression.matches(testString)