does a tee function exist somewhere in F# library?

问题

...or in FSharpx?

let tee sideEffect =
    fun x ->
        do sideEffect x
        x

The usage could be something like

f >> tee (printfn "F returned: %A") >> g >> h

Or is there another simple way to do this?

thanks!

回答1:

ExtCore includes a function called tap which does exactly what you want. I use it for primarily for inspecting intermediate values within an F# "pipeline" (hence the name).

For example:

[| 1;2;3 |]
|> Array.map (fun x -> x * 2)
|> tap (fun arr ->
    printfn "The mapped array values are: %A" arr)
|> doOtherStuffWithArray

回答2:

The closest I've seen is actually in WebSharper. The definition is:

let inline ( |>! ) x sideEffect =
    do sideEffect x
    x

Usage:

(x |>! printf "%A") |> nextFunc

回答3:

As far as I know, a function like this isn't defined anywhere in the F# core library - though the library is missing many standard functions that are quite easy to define yourself, so my recommendation would be just to add it somewhere in your project - your tee seems like the best way to go.

That said, I'd probably prefer using less declarative style if I need side-effects and write something like:

let fResult = f fInput
printfn "F returned: %A" fResult
fResult |> g |> h

This is just a matter of style, but I prefer declarative style for fully declarative code and imperative style when there are side-effects involved. As a bonus, using local variables makes debugging easier. But using a function like tee is an equally good alternative that many people in the F# community would prefer.

来源：https://stackoverflow.com/questions/26672033/does-a-tee-function-exist-somewhere-in-f-library

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