John Carmack on mutable variables • Hacker News Board

Re: John Carmack on mutable variables

#191

Post by kalaksi » Fri, Oct 31, 2025, 11:43 AM UTC

kypro wrote: post #157

y0ned4 wrote: post #124

When I started programming in Haskell, where all variables are immutable, I felt like I was in a straitjacket Then, suddenly, the enlightenment

I've had this experience with going from PHP and JS to typed languages. Many years ago I was a type sceptic, but after being forced to use them, I now can't stand not having strict typing. I'm sure others have written about this, but these days I think good code is code which has a very small area of variability. E.g code which returns a value in a single place as a single type, has a very limited number of params (a…

I initially started programming with C++, then did a bunch of scripting languages and then Rust and C#. I feel like there are pros and cons to strictness.

I don't like all scripting languages, but Python, for example, has a simple syntax and is easy and fast to learn and write. I think it also has a good standard library. Some things can be simpler because of the missing guardrails. But that's also the weakness and I wouldn't use it for large and complex software. You have to be more mindful to keep a good style because of the freedoms.

C++ and Rust are at the opposite end. Verbose to write and more difficult syntax. More stuff to learn. But in the end, that's the cost for better guarantees on correctness. But again, they don't fit all use cases as well as scripting languages.

I've experienced the good and the bad in both kind of languages. There are tradeoffs (what a surprise) and it's probably also subjective what kind of language one prefers. I think my _current_ favorites are Rust, C# and Python.

Re: John Carmack on mutable variables

#192

Post by galangalalgol » Fri, Oct 31, 2025, 11:44 AM UTC

cfontes wrote: post #183

He will like RUST very much.

Carmack had said he likes rust, he just isn't a language zealot. In rust though, the idiom would be to shadow intermediate variables often, which removes the debugger benefit.

Re: John Carmack on mutable variables

#193

Post by sgt » Fri, Oct 31, 2025, 11:45 AM UTC

slifin wrote: post #96

Yeah I wish variables were immutable by default and everything was an expression Oh well continues day job as a Clojure programmer that is actively threatened by an obnoxious python take over

Clojure will always be faster than Python. So you have that, at least.

Re: John Carmack on mutable variables

#194

Post by [deleted] » Fri, Oct 31, 2025, 11:47 AM UTC

rendaw wrote: post #188

EastLondonCoder wrote: post #128

After a 2 year Clojure stint I find it very hard to explain the clarity that comes with immutability for programmers used to trigger effects with a mutation. I think it may be one of those things you have to see in order to understand.

I think the explanation is: When you mutate variables it implicitly creates an ordering dependency - later uses of the variable rely on previous mutations. However, this is an implicit dependency that isn't modeled by the language so reordering won't cause any errors. With a very basic concrete example: x = 7 x = x + 3 x = x / 2 Vs x = 7 x1 = x + 3 x2 = x1 / 2 Reordering the first will have no error, but you'll get t…

[deleted]

Re: John Carmack on mutable variables

#195

Post by mavhc » Fri, Oct 31, 2025, 11:47 AM UTC

Really should invent a new name if you don't want your variables to vary

Re: John Carmack on mutable variables

#196

Post by pvdebbe » Fri, Oct 31, 2025, 11:49 AM UTC

christophilus wrote: post #89

jandrewrogers wrote: post #16

Earlier quoted context omitted.

Pure functional works great until it doesn't. For a lot of systems-y and performance-oriented code you need the escape hatches or you'll be in for a lot of pain and annoyance. As a practical observation, I think it was easier to close this gap by adding substantial functional capabilities to imperative languages than the other way around. Historically, functional language communities were much more precious about the…

F# isn’t purely functional, though, and strikes a nice balance. I just don’t really like the .NET ecosystem, being 100% Linux these days, as it always seems slightly off to me somehow.

Same. I strikes me a great shame that there aren't great F#-like languages that targeted the JVM.

Re: John Carmack on mutable variables

#197

Post by ForHackernews » Fri, Oct 31, 2025, 11:49 AM UTC

TZubiri wrote: post #174

sgarland wrote: post #168

Dumb question from a primarily Python programmer who mostly writes (sometimes lengthy) scripts: if you have a function doing multiple API calls - say, to different AWS endpoints with boto3 - would you be expected to have a different variable for each response? Or do you delete the variable after it’s handled, so the next one is “new?”

I think renaming an old variable is a common and sensible way to free a resource in python. If there are no valid names for a resource it will be garbage collected. Which is different in languages like C++ with manual memory management. John Carmack is a C++ programmer apparently that still has a lot to learn in python.

But wouldn't you do that inside a function or a loop body?

Re: John Carmack on mutable variables

#198

Post by JonChesterfield » Fri, Oct 31, 2025, 11:51 AM UTC

MrNet32823 wrote: post #153

Jonathan Blow had strong objection with const keyword. I forgot because i did not understand at that time. Does anyone with jai experience have a counter point to that.

I believe the standard counterargument goes:

- either it's transitive, in which case your type system is very much more complicated

- or it isn't, in which case it's a near useless liability

Naturally C++ runs with the latter, with bonus extra typing for all the overloads it induces.

Re: John Carmack on mutable variables

#199

Post by JonChesterfield » Fri, Oct 31, 2025, 11:53 AM UTC

shmerl wrote: post #24

Proposing making immutable by default in C or C++ doesn't make sense due to backwards compatibility reasons. New languages like Rust have easier time making better choices with immutable by default.

Could be a compiler flag. -const-by-default. Would probably mean you need to scatter mutable across the codebase to get it to compile, but I expect some people would like to have every local annotated as const or mutable.

Re: John Carmack on mutable variables

#200

Post by criddell » Fri, Oct 31, 2025, 11:58 AM UTC

y0ned4 wrote: post #124

When I started programming in Haskell, where all variables are immutable, I felt like I was in a straitjacket Then, suddenly, the enlightenment

How does Haskell deal with things like memory-mapped I/O or signal handlers where the value of a variable can be changed by factors outside of the programmer's control?