It's pretty much what I mean when calling Haskell hard to learn. For me it's also been a steep learning curve, and my experience hasn't been altogether different than yours.
I started out maybe 5 years ago following tutorials, reading up on all the metaphors about Monads and doing project Euler problems.
After a while I started to tackle some small web related things with Haskell and had exactly your experience of running into a lack of understanding of how the system works and wrapping my head around functional datatypes.
I pretty much gave up on Haskell as a practical language at that point, but something kept me coming back once in a while.
Then at a point I had a use for making a small web service fast and the Node prototype I made performed badly and crashed in spectacular ways under high loads. I found Snap and made a quick prototype in Haskell. At that point the experience of years of small experiments must finally have made something click. In a very short time I had a very fast service using almost no memory. It's deployed in production (as a part of http://www.webpop.com) and has been extremely stable.
By now I think I've crossed some kind of barrier, and feel like I'm both being productive and having fun when writing Haskell, but it really didn't come easy to me and all else being equal my experience tells me that a good deal of my colleagues would have an even harder time.
I think part of the issue with learning haskell is that it seems to invert the typical learning strategy for programming languages. Usually the best advice is read a little, then write a lot. Typically you can just look and some published code and go "ah yes that's how you do it". But I find, for better or worse, Haskell really requires you to understand before you code. Which in the end means your study to code ratio is very different than almost any other language.
Most languages, even lisps, are somewhat tolerant of 'programming by guessing' for beginners. Usually you write terrible code that works, learn more and see what you did wrong. Haskell is very unforgiving of this, if you don't understand why it works it probably won't
I think you're wrong at "if you don't understand why it works it probably won't".
While I long given up PUI (Programming Under Influence) I still occasionally do some in Haskell. After a litre of beer I am pretty dumb, but I can follow clues from compiler to get something working.
Most of the time, it works the next day, when I sober. That's in contrast with C/C++. Scripting languages give some power like that, but I can screw myself with them much more violently.
In my humble opinion, Haskell is the language of choice for drunken programmers.
I recently had that same epiphany. For fun, I decided to re-implement a simple chat server I wrote a while back in Erlang. I found that everything clicked - the type system worked with me instead of against me, and I was able to create prototypes as quickly as I could think of them. But, it took two years of thinking about Haskell before I could synthesize code in it. (code here: https://github.com/dmansen/haskell-chat)
I started out maybe 5 years ago following tutorials, reading up on all the metaphors about Monads and doing project Euler problems.
After a while I started to tackle some small web related things with Haskell and had exactly your experience of running into a lack of understanding of how the system works and wrapping my head around functional datatypes.
I pretty much gave up on Haskell as a practical language at that point, but something kept me coming back once in a while.
Then at a point I had a use for making a small web service fast and the Node prototype I made performed badly and crashed in spectacular ways under high loads. I found Snap and made a quick prototype in Haskell. At that point the experience of years of small experiments must finally have made something click. In a very short time I had a very fast service using almost no memory. It's deployed in production (as a part of http://www.webpop.com) and has been extremely stable.
By now I think I've crossed some kind of barrier, and feel like I'm both being productive and having fun when writing Haskell, but it really didn't come easy to me and all else being equal my experience tells me that a good deal of my colleagues would have an even harder time.