I want to write just curl 8000 to work as curl localhost:8000.

I’ve come up with the following zsh function so far:

function curl() {
    local first_arg="$1"
    if [[ "$first_arg" =~ ^([0-9]{4})(.*)$ ]]; then
        local modified_url="localhost:${first_arg}"
        command curl "$modified_url" "${@:2}"
    else
        command curl "$@"
    fi
}

But obviously, the url is not guaranteed to be the first argument, such as curl -H '...' localhost:8000. Is there a robust existing solution for such needs?