(Swift) Call function in guard statement

I am trying to call a function called 'nextPage' in a guard statement, but it is saying '()' is not convertible to 'Bool'. What do I need to do in order to call this function

@IBAction func nextPressed(_ sender: Any) {
    let geoCoder = CLGeocoder()
    geoCoder.geocodeAddressString(address) { (placemarks, error) in
        guard
            let placemark = placemarks?.first,
            let latVar = placemark.location?.coordinate.latitude,
            let lonVar = placemark.location?.coordinate.longitude,
            nextPage() // Error - '()' is not convertible to 'Bool'
            else {
                print("no location found")
                return
        }
    }
}

The guard statement is used to check if a specific condition is met. You cannot put a function that doesn't return true or false in that statement.

Reference: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html

I believe that what you are trying to accomplish is

@IBAction func nextPressed(_ sender: Any) {
        let geoCoder = CLGeocoder()
        geoCoder.geocodeAddressString(address) { (placemarks, error) in
            guard
                let placemark = placemarks?.first,
                let latVar = placemark.location?.coordinate.latitude,
                let lonVar = placemark.location?.coordinate.longitude
                else {
                    print("no location found")
                    return
            }

            // will only get executed of all the above conditions are met
            nextPage() // moved outside the guard statement

        }
}