export function undefList<T, U>(opt: T | undefined, fn: (opt: T) => U) {
    return opt === undefined ? [] : fn(opt)
}

export const optFlag = (flag: string, opt: string | undefined) => undefList(opt, opt => [flag, opt])

/**
 * Generate a switch flag, like "--rebuild", "--nobuild"
 */
export const optSwitch = (flag: string, opt: boolean | undefined) => undefList(opt, opt => opt ? [flag] : [])