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Serializing functions
f#functionalweb

EDIT: Please move this into the right forum, thank you!!

I've been doing some undergraduate research in the line of computational intelligence, and I'm not entirely sure how to go about storing anonymous functions for retrieval later.

I need to find some way to store the result of some function a -> (b -> a) as data that can then later be loaded from a file by a web server. This result is itself a function, and the function generating this result will itself be supplied at run time by a researcher.

Reading through some documentation it seems that delegates are just pointers and you can't simply load them back up from a file. However, I will have to be able to load and compile these functions at run time and have them accessible to the web server's C# code.

I am aware that I'm crossing beyond the design parameters of a strictly typed functional language here, since the function cannot be type checked ahead of time and its correctness has to be shown when it is loaded from a file. I still hope that there is a solution to this problem.

I know that this is probably a complicated subject in and of itself, unless .NET and F# can do very elegant things with storing arbitrary IL to be compiled later of which I am not aware. I am hoping this is the case.

Failing the existence of a reasonably simple solution I have an alternative (but complicated) method in mind involving interaction with an R interpreter session.

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When you say "supplied at runtime" -- how will it be supplied?

This probably won't help, but F# closures and function results can be serialized using binary serialization. But of course that requires the original DLL containing the IL.

By on 11/30/2009 2:18 PM ()

Through a file stored on the server which will be loaded when the server starts; so not at compile time.

If F# closures can be serialized then that's good news, from what I read on delegates the problem was that the actual object itself was just a pointer and if it was serialized it could not be deserialized again in a useful way, but if that's not true then this whole problem has become much more straightforward.

In that case, I can, at runtime, accept a function that generates the trained classifier (another function) when given a training set and then store that trained classifier to a binary file, loading it again when the server is restarted?

By on 11/30/2009 2:57 PM ()

If the functions are being provided via a DLL, then binary serialization should work fine, assuming you have all the DLLs involved. F# closures are compiled to regular objects (they aren't delegates, but even a delegate representing a closure will need a backing object; you might be able to reflect on the delegate and figure out the methodinfo and instance object...).

For example:

let f x = (fun y -> x + y)

Then applying f to some value will generate an object containing x, and the code for the function. That part will serialize (or did in earlier versions of F#; I have not tried it recently). But note this is not version safe; any changes to the compiled DLL can render the serialized object useless -- it's rather brittle.

By on 11/30/2009 3:28 PM ()

So provided that the context in which the functions are being loaded at runtime is the same as which they were originally being serialized in, it should work normally with binary serialization without any extra effort being needed? That will help.

How do you unbox the function after you load it? F# seems to want to restrict anything that gets unboxed to values.

By on 11/30/2009 3:59 PM ()

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