Create alist of Async objects for F# parallel processing

Question

I know this is not very F# like, but I would like to do the following

[a; b; c; d]
|> Async.Parallel
|> Async.RunSynchronously
|> ignore

where a, b, c and d are generated by a function like this

let myasync (stringparameter: string) = [async{some_code}]

where some_code is for getting information from Internet and saving to database. The function itself should return nothing (returns unit).

I want to create [a,b,c,d] by using

let mutable mylist = []
for i in [1..n] do
 myfunction
 mylist <- List.append mylist myfunction

I got the error: The expression was expected to have type 'a list' but here has type 'string -> Async list'

Any help would be greatly appreciated thanks!

• Sergey Berezovskiy: Where do you get the value for stringparameter? Is it the same for all generated functions?
• corbyn3: Stuart''s second solution works perfectly for me. I was able to get a list of <Async>. I tried to do something similar but did not know I had to use the yield keyword. @SergeyBerezovskiy stringparameter is actually from a global variable which absolutely does not play nice with async parallel. I am rewriting the function now so that it will work more F# like. As of now, I do not get the intended effect but I am marking this question as answered because this step is finished. I have another question for the rewrite actually =(

Answer 1

The immediate error you are seeing is because List.append wants 2 list parameters, it's not like Array.Add(), you can fix it by doing the following:

let mutable mylist = []
for i in [1..n] do
 myfunction
 mylist <- List.append mylist [myfunction]

However, there are more succinct ways to do this without using mutability. Example:

let mylist =
 [ for i in [1..n] do
 let myfunction() =
 async {
 // your code
 return () }
 yield myfunction ]