Kuba Ciechowski
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Http call using F# and HttpClient

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Kuba Ciechowski
·Oct 24, 2021·

1 min read

It took me a few tries to finally call an HTTP endpoint using F#.
I've ended up with this code:

let result =
    async {
        let client = new HttpClient()
        let url = "https://api.frankfurter.app/latest?amount=10.99&from=USD&to=PLN"

        let! result =
            |> Async.AwaitTask

        printfn $"10.99 in USD is {result.Rates.PLN} in PLN"

result |> Async.RunSynchronously

For my taste, it is very similar to the C# code.
The most significant difference lies in the async block. It doesn't run until you do it explicitly!
In the C#, when you create a task, you have no control over when it starts. I've described one of such scenarios here.

Only after calling Async.RunSynchronously the actual workflow runs. It reminds a bit of await instruction in C#, but the inner working is different.

The complete code is available on gist.

I like this functional approach with cold workflows. It seems more intuitive to me. One downside I can see is that it may require more code. But I don't have enough experience with F# to be sure.

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