why do you need to explicitly return an HttpHandler when you need the HttpContext?

[Melomaniash]

i'm confused as to why the docs state that you have to return an httphandler explicitly when you need the context.

bellow i wrote the function as stated in the docs and then tried writing it directly into the function.

let addExampleRecord =
        fun (next : HttpFunc) (ctx : HttpContext) ->
            task {
                let! exampleRecord = ctx.BindJsonAsync<ExampleRecord>()
                do! ExampleDataModule.storeExampleRecord exampleRecord

                return! Successful.OK exampleRecord next ctx
            }

let addExampleRecord2 (next : HttpFunc) (ctx : HttpContext) =
    task {
        let! exampleRecord = ctx.BindJsonAsync<ExampleRecord>()
        do! ExampleDataModule.storeExampleRecord exampleRecord

        return! Successful.OK exampleRecord next ctx
    }

Both functions worked. So my question is, is there a difference between these 2 functions? and if there is, what is it?

[dustinmoris]

Hi, great question and the answer is that there is no difference.

However, there are two reasons which I can think of why some people prefer the first case:

1. You can annotate the return type to be HttpHandler and then let the linter and compiler help you to put the curried parameters in the correct order and make sure that the return type matches what a HttpHandler expects. It's a facility to help write correct code.
2. If you have more curried arguments before the next and ctx then you could run some work in advance before the HttpHandler part is being returned.

Example:

let addExampleRecord (foo : string) (bar : int) =
        // Do some work only once here using foo and bar
        let fooBar = foo + bar.ToString()
        fun (next : HttpFunc) (ctx : HttpContext) ->
            task {
                let! exampleRecord = ctx.BindJsonAsync<ExampleRecord>()
                do! ExampleDataModule.storeExampleRecord exampleRecord
                // Use fooBar here...
                return! Successful.OK exampleRecord next ctx
            }