I have tried to use Haskell a number of times in the past ~5 years for small-scale projects and witnessed others try to use it, and most of these projects (actually I think all) have resulted in failure / rewrites in more simple/plain-vanilla languages like Python/Go. I keep thinking Haskell is interesting, but at some point I had to force myself to stop investing time in it because I kept concluding it's not a good investment of time for a move-fast/practical person like me. I again had to remind myself when I read this post.

Some reasons I remember for the various failures, in no particular order:

- steep learning curve = experienced (in other languages) programmers having a tough time not being productive for weeks/months in the new language, with no clear payoff for the kind of projects they're working on

- sometimes/often side-effects/states/global vars/hackyness is what I want, because I'm experimenting with something in the code; and if I'm not sure if this code will be around in 3 months, I want to leave the mess in and not refactor it

- in general, I think all-the-way pure no side effects is too much; I think J.Carmack said sth along the lines: Haskell has good ideas which should be imported into more generally useful languages like C++/etc, eg. the gamestate in an FPS game should be write-once, it makes the engine/architecture easier to understand (but in general the language should support side-effect)

- I found the type system to be cumbersome: I kept not being able to model things the way I wanted to and running into annoyances; I find classes/objects/templates etc from the C++/Java/Python/whatever world to be more useful for modeling applications

- when the spec of the system keeps changing (=the norm in lean/cont.delivery environments), it's cumbersome/not practical to keep updating the types and deal with the cascading effects

- weird "bugs" due to how the VM evaluates the program (usually around lazyness/lists) leading to memory leaks; when I was chasing these issues I always felt like I'm wasting my time trying to convince the ghc runtime to do X, which would be trivial in an imperative language where I just write the program to do X and I'm done

- cryptic ghc compile errors regarding types (granted, this is similar in C++ with templates and STL..)

- if it compiles it's good => fallacy we kept running into

- type system seemed not a good fit for certain common use-cases, like parsing dynamic/messy things like json

Working at Facebook for the last year and seeing the PHP/Hack codebase which powers this incredibly successful product/company has further eroded my interest in Haskell: Facebook's slow transition from PHP to Hack (=win) shows that some level of strictness/typing/etc is important, but it's pointless to overdo the purity. Just pick sth which is good enough, make sure it has outstanding all-around tooling, have good code-review, and then focus on the product you're building, not the language.

I'm not saying Haskell is shit, I just don't care about it anymore. I'm happy if people get good use out of it, clearly there are problem spaces that are compact, well-defined and correctness is super-important (like parsing).