Obligatory Promises Request

Since promises are apparently cool right now, I feel like I should raise this issue.

We shouldn't really have blocking HTTP requests. Can we have the verbs return a promise object, such that I can do:

Curl.get("http://jsonip.com").then((res) -> println(res.text))

Then would take three arguments: onResolved, onError, and onProgress.

I would express it like this:

type Promise
    then::Function
    resolved_callbacks::Vector
    rejected_callbacks::Vector
    progress_callbacks::Vector
    resolve::Function
    reject::Function
    progress::Function

    function then(on_resolved, on_error, on_progress)
        # push callbacks into queues
    end

    function resolve(value)
        # if no handlers left return
        # shift handler off queue
        # invoke handler with value
        # recurse
    end

    function reject(error)
        # if no handlers left return
        # shift handler off queue
        # invoke handler with value
        # recurse
    end

    function progress(value)
        # if no handlers left return
        # shift handler off queue
        # invoke handler with value
        # recurse
    end

    function Promise()
        new(then, [], [], [], resolve, reject, progress)
    end

end

get = function (url)
    promise = Promise()

    on_complete(data) = promise.resolve
    on_error(error) = promise.reject
    on_progress(data) = promise.progress

    do_curl() # with appropriate arguments

    promise;
end

Of course that doesn't allow us to chain then calls, but in general I find chaining to be very difficult in Julia. There may be a way to do it. We could also just pass in handlers as a vector of functions instead of just one function.

Open to other approaches too.

forio / Curl.jl

Obligatory Promises Request #6