Lets say I wanted to scrape a webpage, and extract some data. I'd most likely write something like this:
let getAllHyperlinks(url:string) =
async { let req = WebRequest.Create(url)
let! rsp = req.GetResponseAsync()
use stream = rsp.GetResponseStream() // depends on rsp
use reader = new System.IO.StreamReader(stream) // depends on stream
let! data = reader.AsyncReadToEnd() // depends on reader
return extractAllUrls(data) } // depends on data
The let! tells F# to execute the code in another thread, then bind the result to a variable, and continue processing. The sample above uses two let statements: one to get the response, and one to read all the data, so it spawns at least two threads (please correct me if I'm wrong).
Although the workflow above spawns several threads, the order of execution is serial because each item in the workflow depends on the previous item. Its not really possible to evaluate any items further down the workflow until the other threads return.
Is there any benefit to having more than one let! in the code above?
If not, how would this code need to change to take advantage of multiple let! statements?
