I've learned Haskell at university too. That doesn't prove anything though does it? At the time I've found it useless and plain wrong ... it is much later that I learned to appreciate it and value what it brings to the table...much much later.
It's nice to have language support for functional style (let, for example) where that is appropriate for the problem at hand, but you can write in that style without the language support easily enough.
On the other hand, when FP style is not appropriate for the problem at hand, it really, really gets in the way, and that's the case a lot of the time. Many if not most problems (outside of writing compilers for FP languages) don't really fit the functional style, and have to be made to fit.
Experienced devs will choose appropriate tools for the problem at hand. Me, I like adaptive tooling that I can bend to fit the problem, which is why I like dynamic OO languages, internal DSLs and Domain Modeling[2] in general.
In fact, I think the current tools are still a little too inflexible for this, which is why I am creating a language to address some of these issues: http://objective.st
FP seems to be more about bending the problem to fit the tooling, which I guess may work for a specific kind of mindset.
[1] http://en.wikipedia.org/wiki/Higher_order_message
[2] http://www.amazon.com/Domain-Driven-Design-Tackling-Complexi...
Some examples would be helpful here.
Anything with state comes to mind. The text field I am typing this into, for example. I type on my keyboard and the state of the text field changes, and after I hit "reply", the state of the page changes with a comment appended. Before/after.
Yes, you can implement this by creating a completely new page containing the concatenation of the old page with the comment, but externally (when you visit the URL), the state of that page has changed. So if you choose to implement the problem in a functional style, you have to bridge that gap somehow between that style and the problem at hand.
Any sort of document processing done on computers in Word, Excel (regarding the document itself, not the one way dataflow constraint program inside), OpenOffice, PowerPoint, Pages, Keynote, Quark XPress, InDesign, Photoshop, Illustrator etc. People use these programs to change the state of documents. That is the purpose of these programs.
Anything that interacts with the world, for example the user interface.
Or Wikipedia. Pages change, sometimes because there is new information, sometimes because something in the world has changed. Or most any other web site.
Really, the world (a) has (a lot of) state and (b) that state is changing incessantly. It is not (a) stateless or (b) immutable.
But don't take it from me: "In the end, any program must manipulate state. If it doesn't, there is no point in running it. You hit go and the box gets hotter" - Simon Peyton-Jones. https://www.youtube.com/watch?v=iSmkqocn0oQ&t=3m20s
It's funny that this guy claims fitting the problem to suit FP is a bad thing. But fitting the problem to suit OOP is seemingly a good thing. There is no difference really. All problems have to be made to fit your tooling and practices in same way. The difference is how much squashing is required and the two or three second decision it takes to select the right tool. Only performance optimisations really warrant falling back to mutation of state, other than IO of course. The default should always be immutable. Don't let some brain dead OOP-only troll deter you from seeing the light.
He is speaking is riddles, like pseudo academics love to. Seriously, he is suggesting you can't have an editable text box on a GUI, written in a language like Scala, F# or OCaml? What a moron. (This link will prove particularly embarrassing to a certain person here: http://www.scala-lang.org/api/2.10.2/index.html#scala.swing....) He is arguing an argument that doesn't even exist here, but one that only exists in his own head.
Pure FP, much like pure OOP, is utter shit and painful. The sweet spot is reached by mixing the two and using a multi-paradigm language, ala F#, Scala, OCaml, etc.
I said I like hybrid OO-FP languages for business productivity, rather than concentrating on meaningless software architecture astronautics like that "Blue Book" you linked. I've read it, yes starting from chapter 11, and while I took it on board I find many of its ideas and practices completely toxic now. Just like Gang of Four patterns and the inane amount that OOP inherently relies upon them.
Then you go off on some academic rant about "well in 1989" (no one cares) and HPC computing (no one cares, it's hardly relevant either). FP has progressed a lot since 89 but you're seemingly too old and set in your purely OOP ways to realise it. Carry on. But take a look at a modern OO-FP multi paradigm language and feel enlightened.
If you carry on down the path of ranting about FP because, shock horror, yes it is slower than imperative code then you'll look even sillier. Not that anyone really cares about some randomer making himself look silly by poo-pooing a whole programming language paradigm whilst paradoxically claiming he always likes to choose the right tool for the job. I guess your jobs have just never been varied enough then?
PS: Higher order messaging is just function composition with presumably a dash of actors. Congrats on reinventing a functional programming concept. But it perfectly illustrate the ignorance so prevalent in individuals that only know OOP and will attack anything that isn't OOP.
Funny, my age seemed to be important when I was "young and inexperienced". Now "no one cares"...and I am "too old and set in my ways". Which is it? Both? Does my age matter or not? Both again?
Hint: if your conclusion remains the same, but your reasons for that conclusion are this inconsistent, then your conclusions is almost certainly not supported by those reasons. In the words of Popper, an "immunized" theory, meaning it is immune to falsification by empirical evidence.
Anyway, as you gain experience, you will probably appreciate the wisdom of domain modeling. Or remain ignorant. Not sure how the GoF Pattern book got into this discussion, but note that it is largely a description of workarounds for non-dynamic OO languages.
The 6x slower performance was relevant for "Data Parallel Haskell", because performance is pretty much the only reason for doing that sort of parallelism in the first place, as I explained. HPC was relevant because they had been doing the thing that was claimed "impossible" by SPJ in languages not like Haskell...in FORTRAN (which I hope we can agree is not all that much like Haskell).
Had you paid attention, you would have noticed that I use functional techniques when appropriate. I just don't buy the inflated claims, which have been consistently inflated and consistently unsupported by evidence for well over 2 decades now ... and object to arrogant ignorance such as that which you have amply displayed and continue to display.
To call HOM derivative is not exactly a deep insight, when I very specifically told you that it was derivative (and the papers are also very clear about that). However, you display fundamental misunderstanding of not just HOM (which could be forgiven), but also OOP and FP: HOM is exactly not "function composition". OOP languages have had higher order functions ("blocks" in Smalltalk) for decades, and these can be and have been composed quite easily. The point of HOM is that the first order mechanism in an OOPL is messaging, so having functions as the higher order mechanism is inconsistent. HOM creates a HO mechanism that is based on messaging instead of functions, hence HOM. Actors are an unrelated concept.
HOM? Don't make me laugh. It's just more shit for the objective world to work around limitations of the languages. A message is just an object that can be and queued somewhere, and potentially serialized. That's not special.
- Loves dynamic languages. Check. - Loves OO. Check. - Loves DDD Blue Book. Check. - Invents "new" programming design patterns all by himself believing he is the sole inventor. Check. - Dabbled with an FP language in '89 and hasn't touched FP ever since. Check. - Created his own shitty programming language to try to improve upon OOPs limitations. Check. - Dares to talk down to anyone more experienced or that disagrees with him. Check.
Yeah, I wouldn't employ you either.