Collection.swift

// Swift Foundation
func prefix(while predicate: (Self.Element) throws -> Bool) rethrows -> Self.SubSequence
func map<T>(_ transform: (Self.Element) throws -> T) rethrows -> [T]

// prefixMap (new)
extension Collection {
    @inlinable func prefixMap<T>(_ transform: (Self.Element) throws -> T?) rethrows -> [T] {
        var result = [T]()
        for element in self {
            if let transformedElement = try transform(element) {
                result.append(transformedElement)
            }
            else {
                break
            }
        }
        return result
    }
}