promise example

proc zipnmail {dir urls} {
    set downloads [all [lmap url $urls {
        [pgeturl $url] then [lambda {dir url http_state} {
            save_file $dir $url [dict get $http_state body]
        } $dir $url]
    }]]
    set zip [$downloads then [lambda {dir dontcare} {
        then_chain [pexec zip -r pages.zip $dir]
    } $dir]]
    set email [$zip then [lambda dontcare {
        then_chain [pexec blat pages.zip -to someone@somewhere.com]
    }]]
    $email done [lambda {dontcare} {
        tk_messageBox -message "Zipped and sent!"
    }]
}