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"Live" F#
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I love F# interactive command line in Visual Studio. I saw a note by Don about how he often develops his algorithms in the REPL, even instantiating little GUI widgets to help him see what is going on as the algorithms proceeds.

I would like to know how the REPL works. I doubt F# has an interpreter for the interactive development and a compiler for the VM. I also don't see how expressions might be read, compiled, executed...while maintaining context for the previously evaluated expressions (for example, changing attributes of a running GUI).

So how is it done exactly, how would I do it if I wanted my own REPL outside of Visual Studio (or if I wanted to integrate F# in my own application)?

Furthermore, I am interested in 'interactive' and 'live' programming beyond the REPL. It might seem strange to some, but Excel is so liked in the financial world because one can feed in a market data feed, run expressions against, filter it, color cells based on it...sometimes even generated trades interactively. If some algorithm doesn't make sense, just print out all values on the screen.

Mathematica 6.0 has some interesting features, which let users pass in functions as parameters to other functions which dynamically build a user interface to display data (or visualize data) while letting users play around with input parameters.

Lisp is famous for providing the ability to modify running programs.

The basic motivation is that writing a large block of logic as a black-box doesn't work very well when the system might need to change while it is running, the system can't really be brought down, programmers might need to see what is going on in the black-box...but may not always anticipate this need while developing. Another way to look at it is that I need to run the program while I'm programming it (or program it while it is running).

I'm encouraged that F# programmers don't seem opposed to such ideas. Yet, I don't really know how to program such flexible systems. OSGI type run-time loadable classes don't go far enough.

As you can tell, I'm not even sure how to ask the right question. Any ideas how to build such systems?

.

Hi falcon,

this is an excellent question - and a feature that is commonly requested (for my contributions see here and here.)

As far as I understand Fsi emits MSIL into an in-memory assembly and takes care of maintaining state itself - the details are in fsi.fs. I would dearly love to see this functionality deeply integrated into FSharp's language and core library but as it stands it's not even clear that integrating this functionality into an application is legal!

It's also possible that extensions are necessary to the fsharp type system to support this in a robust fashion similar to those in MetaOcaml and Gregory Neverov's Metaphor. But what do I know?

I hope that the reason for the silence from the fsharp team is that they hard at work creating the first (and best) commercial multi-stage programming language which would allow the type-safe dynamic execution that Fsi shows is possible.

I do believe that this functionality could bring about a paradigm-shift in the way scientists and engineers collaborate.

regards,

Danny

By on 10/3/2008 12:46 PM ()

Thanks Danny,

There are some interesting possibilities. Most people trying out F# will necessarily be those of us who are not quite satisfied with our existing environments (Java in my case). As we learn a new language, learning new techniques of development will be an easier sell. That's why the culture of F# can do things the cultures of Java and C# probably couldn't.

Although I don't regularly use various math packages such as Mathematica, Matlab, Maple, I like how programming and interactive problem solving is pretty much the same thing.

I want to be able to sit with a competent domain expert for a few hours and just solve the problem interactively...then go back and do all the software engineering stuff to make it maintainable.

In any case, I am looking forward to F# moving closer to actual release (which will free up the experts to do some more cool things).

By on 10/7/2008 7:11 AM ()

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