How hard is it to change from OOP thinking to pure FOP thinking in .net?

Question

I have been working with c# for many years, since beta. I am having a bit of a time of it, moving from OOP to FOP. I started out with the concepts of procedural programming and functional composition in the late 80's and have been doing OO since around '95 when UML was in its infancy where I was programming in Delphi with the multi-paradigm approach of Procedural and OO.

Are there any good books suggestions, to helping the transition over to functional Programming from a deep rooted OO programmer. I tried a Haskell book, but it seemed to require some background in the subject and was very unapproachable.

I have a couple of O'reilly, Apress books on F#, but it all seems a bit woolly and half way house, of just getting the job done. It also mixed Objects up with functions to suit the needs.

F# seems to forgive me in my OOP thinking a lot more than Haskell, but I think to get the true benefits I need to get into the mindset of FOP to get the best out of the code. I have read around functional programming for about 2 years in between my day to day c# stuff. But I feel I am not getting into the thinking.

I am pretty sure that there are many people out there like myself. Any answers would be I think a great help to a lot of C# guys wishing to move over to F#. Especially with many big hitters in the market place asking for F#. I am a contractor who needs to get up to speed as soon as possible.

thank you in advanced.

Answer 1

This is definitely subjective, but I think that many people are asking similar questions. I certainly did when I started learning F# (as someone with C# experience). Here are some assorted ideas:

• Pick the right learning problems - The best way to learn functional programming is to start working on some non-trivial projects. If you pick a project that is easy to solve in the OO way, then you'll probably lean towards OO solution. However, if you choose some project that naturally fits FP solutions, then you'll learn something. In my case, I worked on translator from F# quotations to JavaScript, which involves a lot of recursive processing and discriminated unions.

• Don't try to be perfect - If you try to write something in the functional way, it may not be perfect at the first attempt. Don't worry about that (and don't say to yourself that you could do better in OO way). You can do better in the FP way as well - it just takes some time to find out how to do that.

• Try to be purist - If you start learning Haskell then you'll have to write pure functional code. F# doesn't enforce that, but I don't think that makes F# less suitable for learning functional programming. If you know C# and .NET, you can reuse a lot of your experience. Just try to be more strict to yourself and avoid using non-functional constructs like mutable state and inheritance - they are sometimes useful, but you can use them after you learn to think in the FP way.

And a little shameless plug - answering a question like this was one of the key motivations for my Real World Functional Programming book, so maybe that could help...

Answer 2

Are there any good books suggestions, to helping the transition over to functional Programming from a deep rooted OO programmer

The Structure and Interpretation of Computer Programs (SICP):

• Book: http://mitpress.mit.edu/sicp/full-text/book/book.html
• Video lectures: http://groups.csail.mit.edu/mac/classes/6.001/abelson-sussman-lectures/

His course seems to focus mostly on functional composition. It is in LISP, but it is less about the language, and more about the abstract concepts.

I don't think he says much (or anything) about pure FP, but I haven't really read all of it, either :) The concepts and way of thinking should still be highly applicable, though.

Answer 3

I believe that to really understand functional programming you must first reorganize all your knowledge about the ways to implement different things (e.g. you have to understand that objects may be represented as hash maps or even associative lists, not just as records). Also you will need to start thinking in terms of immutable data and pure functions (procedures of no side effect). Then you'll have to compare functional and procedural ways to implement and treat objects.

All of this you can find in SICP - classical book for learning not only FP, but programming in general. To understand functional way you won't have to read all book, but at least first 3 chapters.

After you understand main FP concepts and are able to implement anything in it's style, read any book on statically typed languages. E.g. Apress books on F# will be much easier to read.

Answer 4

Learn You a Haskell is a decent read, though it's probably a bit too basic given you probably already know the syntax of Haskell from one of those books that you picked up...

Moving up a notch, there's Programming in Haskell, which if you scroll down on that page, has a bunch of links to video lectures based on the book given by MS Research's Erik Meijer.

The Equational Reasoning stuff is particularly interesting, if only academically.

In terms of application, that Real-World Functional Programming book given in the other answer looks really nice -- though I haven't read it, so I can't make any judgments.