[throwaway7645]

Haskell may indeed be one of the most advanced languages out there in terms of raw power, but it is very complex (how many monad tutorials does it seriously take to teach one of the most core pieces of the language) and how much category theory do you need to know to be moderately effective? Also, the ecosystem could use some work. An example is the main string library isn't used in favor of a different one. Using the first and obvious one leads to performance worse than python and perl even after you compile. I'm being nitpicky, but anytime someone writes a blog post comparing a programming language to playing darksouls (game where you die thousands of times) I'd say you have an issue.

[tathougies]

Honestly, none. I'm not a category theorist, and have no more understanding of monads than anyone who's used a javascript promise library, and I've been employeed professionally as a Haskell programmer for the past year, contributed libraries back to the community, and given talks in my local area.

Haskell is a language like any other. Many people would like to complicate it, but if you spend the time learning its syntax and semantics, there is very little need to learn the theory.

[data_hope]

I started to write a toy compiler in OCaml. I had some previous experience with Haskell, but in no way an expert. I.e. no category theory background, only shallow exposure to monads.

My "problems" with OCaml started, when I wanted to "map" over a data structure I defined. I ended up having to define custom mapping functions for all container-like data structures I wrote and call them in a non-polymorphic fashion (where I would have just used fmap in Haskell).

Sure, in OCAML I needed to use a parser generator where I would have used megaparsec in haskell, but it was also a tolerable inconvenience.

Trouble started when I needed to track state in the compilation process. I.e. I was generating variable names for temporary results and values, and I needed to track a number that increased. In the end I used a mutable state for it, and it turned out nightmarish in my unit tests.

After a while, I just ported the code base to Haskell and never looked back. The State monad was an easy fix for my mutable state issues. Parser combinators made the parser much more elegant. And many code paths improved, became much more concise. It is hard to describe, but in direct comparison, OCaml felt much more procedural and Haskell much more declarative (and actually easier to read).

The only advantage of OCaml to me is the strict evaluation. I don't think lazy evaluation by default ins Haskell is a great idea.

[ms013]

I assume you were just not interested in passing the state around to the functions that needed it, and preferred the fact that the state monad hides that plumbing for you via bind and return. It's worth noting that there exist Ocaml libraries that provide the same operators and even similar do notation syntax that desugars to bind/return operators (via PPX).

Ocaml does tend to be more verbose than Haskell - it's just the nature of the language syntax. E.g., in Ocaml, one says (fun x -> x+1) vs (\x -> x+1). Similarly, ocaml is cursed by the excessive "in"'s that accompany let bindings. "Let .. in let .. in let ...". That can get annoying.

Interestingly, I had the opposite experience with a commercial compiler project. Haskell's syntactic cleverness (monadic syntax, combinator libraries, etc..) eventually got in the way - it became very difficult to understand what a single line of code actually meant since one had to mentally unpack layers of type abstractions. Migrating to ocaml, the verbosity eventually was more tolerable than the opacity of the equivalent Haskell code once the compiler got sufficiently complex.

My experience may vary from yours. I've been doing Haskell/Ocaml in production for many years, so the pain points I've adapted to are likely different than one working on toy compilers or weekend projects. And no, category theory exposure is not and never has been necessary for understanding Haskell or FP unless one is a PL researcher (and even then, only a subset of PL researchers are concerned with those areas). And one can be quite productive and prolific in Haskell without a deep understanding of monads and monad transformers - the blogosphere has given you the wrong impression if you believe otherwise.

[implicit]

I've done a lot of production Haskell and I've had a similar experience.

In our case, we dealt with it by keeping relatively bare, boring code. We avoided point-free style, crazy combinators like lenses, and complex monad transformer stacks except in the 'plumbing' part of the application that didn't need to change very much.

This paid off in spades as we had a lot of engineers who only ever had to work in the 'porcelain' parts of the application. They got a lot of great work done using abstractions that matched their intuition exactly.

[throwaway7645]

Thanks for the thorough reply and it sounds like you're quite experienced here. Any chance going into more detail with what you do for a living? Do you maintain a compiler for something more mainstream?

[ms013]

I cofounded a company recently that is using code transformation and optimization methods to accelerate data analytics code on special purpose hardware. Our compilation toolchain is all ocaml, and the language that is compiled/transformed/optimized is Python. Prior to this venture, I did similar work - code analysis and transformation, but in that case largely around high performance computing for scientific applications. That tooling was mostly ocaml/Haskell, but not production focused - it was mostly research code.

[a0]

Just want to note that, while not frequently seen, you can use more powerful abstractions (monad transformers, parser combinators, etc) in OCaml.

As an example consider looking at the Angstrom[1] parser combinator library and my Pure[2] functional base library.

[1] https://github.com/inhabitedtype/angstrom

[2] https://github.com/rizo/pure

[haskellandchill]

> (how many monad tutorials does it seriously take to teach one of the most core pieces of the language) and how much category theory do you need to know to be moderately effective?

I believe the answer to both questions is zero. Unfortunately there is pedagogical cruft in the community that makes it appear this way. main :: IO () is comparable to public static void main(args[]) or whatever nonsense in Java.