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> I made a half-hearted attempt to learn Haskell

Try Clojure(script) - everything that felt confusing in Haskell becomes crystal clear, I promise.

> Consider a histogram function.

You can absolutely do this efficiently with immutable structures in Clojure, something like

      (reduce (fn [acc x]
                (update acc x (fn [v] (inc (or v 0)))))
              {}
              coll)

This is O(n) and uses immutable maps. The key insight: immutability in Clojure doesn't mean inefficiency. Each `update` returns a new map, but:

1. Persistent data structures share structure under the hood - they don't copy everything

2. The algorithmic complexity is the same as mutable approaches

3. You get thread-safety and easier reasoning for a bonus

In JS/TS, you'd need a mutable object - JS makes mutability efficient, so immutability feels awkward.

But Clojure's immutable structures are designed for this shit - they're not slow copies, they're efficient data structures optimized for functional programming.

2 comments

> immutability in Clojure doesn't mean inefficiency.

You are still doing a gazillion allocations compared to:

  for (let i = 0; i < data.length; i++) { hist[data[i]]++; }

But apart from that the mutable code in many cases is just much clearer compared to something like your fold above. Sometimes it's genuinely easier to assemble a data structure "as you go" instead of from the "bottom up" as in FP.

Sure, that’s faster. But do you really care? How big is your data? How many distinct things are you counting? What are their data types? All that matters. It’s easy to write a simple for-loop and say “It’s faster.” Most of the time, it doesn’t matter that much. When that’s the case, Clojure allows you to operate at a higher level with inherent thread safety. If you figure out that this particular code matters, then Clojure gives you the ability to optimize it, either with transients or by dropping down into Java interop where you have standard Java mutable arrays and other data structures at your disposal. When you use Java interop, you give up the safety of Clojure’s immutable data structures, but you can write code that is more optimized to your particular problem. I’ll be honest that I’ve never had to do that. But it’s nice to know that it’s there.

The allocation overhead rarely matters in practice - in some cases it does. For majority of "general-purpose" tasks like web-services, etc. it doesn't - GC is extremely fast; allocations are cheap on modern VMs.

The second point I don't even buy anymore - once you're used to `reduce`, it's equally (if not more) readable. Besides, in practice you don't typically use it - there are tons of helper functions in core library to deal with data, I'd probably use `(frequencies coll)` - I just didn't even mentioned it so it didn't feel like I'm cheating. One function call - still O(n), idiomatic, no reduce boilerplate, intent is crystal clear. Aggressively optimized under the hood and far more readable.

Let's not get into strawman olympics - I'm not selling snake oil. Clojure wasn't written in some garage by a grad student last week - it's a mature and battle-tested language endorsed by many renowned CS people, there are tons of companies using it in production. In the context of (im)mutability it clearly demonstrates incontestable, pragmatic benefits. Yes, of course, it's not a silver bullet, nothing is. There are legitimate cases where it's not a good choice, but you can argue that point pretty much about any tool.

If there was a language that didn't require pure and impure code to look different but still tracked mutability at the type level like the ST monad (so you can't call an impure function from a pure one) - so not Clojure - then that'd be perfect.

But as it stands immutability often feels like jumping through unnecessary hoops for little gain really.

> then that'd be perfect.

There's no such thing as "perfect" for everyone and for every case.

> feels like jumping through unnecessary hoops for little gain really.

I dunno what you're talking about - Apple runs their payment backend; Walmart their billing system; Cisco their cybersec stack; Netflix their social data analysis; Nubank empowers entire Latin America - they all running Clojure, pushing massive amounts of data through it.

I suppose they just have shitload of money and can afford to go through "unnecessary hoops". But wait, why then tons of smaller startups running on Clojure, on Elixir? I guess they just don't know any better - stupid fucks.

The topic was immutability, not Clojure?

But ok, if mutability is always worse, why not use a pure language then? No more cowardly swap! and transient data structures or sending messages back and forth like in Erlang.

But then you get to monads (otherwise you'd end up with Elm and I'd like to see Apple's payment backend written in Elm), monad transformers, arrows and the like and coincidentally that's when many Clojure programmers start whining about "jumping through unnecessary hoops" :D

Anyway, this was just a private observation I've reached after being an FP zealot for a decade, all is good, no need to convert me, Clojure is cool :)

> Clojure is cool

Clojure is not "cool". Matter of fact, for a novice it may look distasteful, it really does. Ask anyone with a prior programming experience - Python, JS, Java to read some Clojure code for the first time and they start cringing.

What Clojure actually is - it is "down to earth PL", it values substance over marketing, prioritizes developers happiness in the long run - which comes in a spectrum; it doesn't pretend everyone wants the same thing. A junior can write useful code quickly, while someone who wants to dive into FP theory can. Both are first-class citizens.

> If there was a language that didn't require pure and impure code to look different

I've occasionally wondered what life would be like if I tried writing all my pure Haskell code in the Identity monad.

Same!

Next time I feel an itch to learn a language, I'll probably pick Clojure, based mostly on this comment. Not sure when that will be though.

One doesn't need to "wear a tie" to learn Clojure - syntax is so simple it can be explained on a napkin. You need to get:

1. An editor with structural editing features - google: "paredit vim/emacs/sublime/etc.", on VSCode - simply install Calva.

2. How to connect to the REPL. Calva has the quickstart guide or something like that.

3. How to eval commands in place. Don't type them directly into the REPL console! You can, but that's not how Lispers typically work. They examine the code as they navigate/edit it - in place. It feels like playing a game - very interactive.

That's all you need to know to begin with. VSCode's Calva is great to mess around it. Even if you don't use it (I don't), it's good for beginners.

Knowing Clojure comes super handy, even when you don't write any projects in it - it's one of the best tools to dissect some data - small and large. I don't even deal with json to inspect some curl results - I pipe them through borkdude/jet, then into babashka and in the REPL I can filter, group, sort, slice, dice, salt & pepper that shit, I can even throw some visualizations on top - it looks delicious; and it takes not even a minute to get there - if I type fast enough, I slash through it in seconds!

Honestly, Clojure feels to be the only no bullshit, no highfalutin, no hidden tricks language in my experience, and jeeeesus I've been through just a bit more than a few - starting with BASIC in my youth and Pascal and C in college; then Delphi, VB, then dotnet stuff - vb.net, c#, f#, java, ruby; all sorts of altjs shit - livescript, coffeescript, icedcoffeescript, gorillascript, fay, haste, ghcjs, typescript, haskell, python, lua, all sorts of Lisps; even some weird language where every operator was in Russian; damn, I've been trying to write some code for a good while. I'm stupid or something but even in years I just failed to find a perfect language to write perfect code - all of dem feel like they got made by some motherfluggin' annoyin' bilge-suckin' vexin' barnacle-brained galoots. Even my current pick of Clojure can be sometimes annoying, but it's the least irksome one... so far. I've been eyeing Rust and Zig, and they sound nice (but every one of dem motherfuckers look nice before you start fiddling with 'em) yet ten years from now, if I'm still kicking the caret, I will be feeding some data into a clj repl, I'm tellin' ya. That shit just fucking works and makes sense to me. I don't know how making it stop making sense, it just fucking does.