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F# interactive, redefining events, functions interactively
f#

Hi,

Where one can find more info about how f# interactive compiles the code on the fly? I mean, maybe not specific information, but regarding to my simple question.

Let's assume I interactively create form, and attach some function as the event handler to some button click event. Then, if I modify this function, I have to reattach it to the event, because without it, the old function is called. Is it possible to change this behaviour, or is it because of to the way of how f# interactive compile the code on the fly?

The same situation occurs in simpler example.

Assume following script:

let f() =
printfn "f"

let perform() =
for i=1 to 10 do
f()

If I redefine f function, and call perform(), the old f() is called... I thought it may be because f was inlined or something, but it's just only my guesses...

PS. I even hoped for something like: having some class defined, and its instance is used in the background (let's assume its particular method is called from time to time), and augmenting it with different override of this method, so that there would be possibility to change behaviour of the already running code, but I think it is too hacky (but it doesnn't work and I've got a warning that override augmentations may be deprecated)

.

You can use a "ref" to a function to dynamically later change its behavior in FSI. Here is an example, that demonstrates the issue you're describing (redefining 'f' is not picked up by 'perform') as well as the easy workaround (add a layer of mutable indirection, use a ref to a function and mutate the ref and have perform call through the ref).

> let f() =
- printfn "hi";;

val f : unit -> unit

> let mutable g = ref f;;

val mutable g : (unit -> unit) ref

> let perform() =
- for i in 1..3 do
- (!g) ()
- ;;

val perform : unit -> unit

> perform();;
hi
hi
hi
val it : unit = ()
> let f() =
- printfn "new";;

val f : unit -> unit

> perform();;
hi
hi
hi
val it : unit = ()
> g := f;;
val it : unit = ()
> perform();;
new
new
new
val it : unit = ()
>

By on 11/23/2008 11:21 AM ()

Hi,

Thanks, it works:) This interactive mode is nice, lots of stuff one can do with it, and some of them are pretty hacky:)

By on 11/23/2008 12:18 PM ()

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