VENV_DIR=${VENV_DIR:-~/.local/virtualenv}
_envon()
{
    local venvs cur

    # Get the list of environments
    venvs=$(for x in $VENV_DIR/*; do basename "$x" ; done)
    cur="${COMP_WORDS[COMP_CWORD]}"
    COMPREPLY=( $(compgen -W "${venvs}" -- ${cur}) )
    return 0
}

envon()
{
    source $VENV_DIR/$1/bin/activate
}

complete -F _envon envon