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John Carmack on mutable variables
471–480 of 663 posts
Re: John Carmack on mutable variables
#472Earlier quoted context omitted.
In functional programs, you very explicitly _do not_ need to understand an entire program. You just need to know that a function does a thing. When you're implementing a function-- sure, you need to know what it does. But you're defining it in such a way that the user should not know _how_ it works, only _what_ it does. This is a major distinction between programs written with mutable state and those written without.…
I think you missed the point. I understand that if you writing a simple function with an expected interface/behaviour then that's all you need to understand. Note this isn't something unique to a functional approach. However, somebody needs to know how the entire program works - so my question was where does that application state live in a purely functional world of immumutables? Does it disappear into the call stac…
It didn't disappear; there's just less of it. Only the stateful things need to remain stateful. Everything else becomes single-use.
Declaring something as a constant gives you license to only need to understand it once. You don't have to trace through the rest of the code finding out new ways it was reassigned. This frees up your mind to move on to the next thing.
Re: John Carmack on mutable variables
#473We're all already doing this as the compiler turns everything into SSA form, silly goose.
Re: John Carmack on mutable variables
#474One area that I like to have immutability is in function argument passing. In javascript (and many other languages), I find it weird that arguments in function act differently depending on if they are simple (strings, numbers) versus if they are complex (objects, arrays). I want everything that passes through a function to be a copy unless I put in a symbol or keyword that it suppose to be passed by reference. I made…
> I want everything that passes through a function to be a copy unless I put in a symbol or keyword that it suppose to be passed by reference. JavaScript doesn’t have references, it is clearer to only use “passed by reference” terminology when writing about code in a language which does have them, like C++ [0]. In JavaScript, if a mutable object is passed to a function, then the function can change the properties on…
Thinking on this subject a bit more. I have to wonder if C++ made references just so there is a fast an efficient way to mutate without having to make a copy?
Maybe someone should work on a way to make references in javascript land. Sort of like immer but baked in.
Re: John Carmack on mutable variables
#475After 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.
Clojure also makes it very easy, it'd require too much discipline to do such a thing in Python. Even Carmack, who I think still does python mostly by himself instead of a team, is having issues there.
> it'd require too much discipline to do such a thing in Python
Is Python that different from JavaScript? Because it's easy in JavaScript. Just stop typing var and let, and start typing const. When that causes a problem, figure out how to deal with it. If all else fails: "Dear AI, how can I do this thing while continuing to use const? I can't figure it out."
Re: John Carmack on mutable variables
#476I'm curious where this fits in with single assignment semantics:
int x = 3;
x = 4; // error!
int* p = &x;
*p = 4; // is that an error?Re: John Carmack on mutable variables
#477When 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…
Personally I'd tweak your last sentence to "return statements in the middle of a function."
Early returns at the very top for things like None if you pass in an Option type don't increase the risk of bugs, but if you have a return nested somewhere in the middle it makes it easier to either write bugs up front or especially have bugs created during a refactor. I certainly have had cases where returns in the middle of a beefy function caused me headaches when trying to add functionality.
Re: John Carmack on mutable variables
#478Earlier quoted context omitted.
I think it's because (I'm looking at Haskell in particular) there are a lot of great ideas implemented in them, but the purity makes writing practical or performant time-domain programs high friction. But you don't need both purity and the various tools they provide. You can use the tools without the pure-functions model. In particular: My brain, my computing hardware, and my problems I solve with computers all feel…
My problem with functional languages is there never seems to be any easy way to start using them. Haskell is a great example here. Last time I tried to learn it, going on the IRC channel or looking up books it was nothing but a flood of "Oh, don't do that, that's not a good way to do things." It seemed like nothing was really settled and everything was just a little broken. I mean, Haskell has like what, 2, 3, 4? Maj…
> I mean, Haskell has like what, 2, 3, 4? Major build systems and package repositories? It's a quagmire.
Don't know when was the last time you've used Haskell, but the ecosystem is mainly focused on Cabal as the build tool and Hackage as the official package repository. If you've used Rust:
- rustup -> ghcup - cargo -> cabal - crates.io -> hackage - rustc -> ghc
Re: John Carmack on mutable variables
#479Earlier quoted context omitted.
I think the advantage is often oversold and people often miss how things actually exist on a continuum and just plainly opposing mutable and immutable is sidestepping a lot of complexity. For exemple, it's endlessly amusing to me to see all the efforts the Haskell community does to basically reinvent mutability in a way which is somehow palatable to their type system. Sometimes they even fail to even realise that it'…
If you read through the Big Red Book¹ or its counterpart for Kotlin², it's quite explicit about the goals with these techniques for managing effects, and goes over rewriting imperative code to manage state in a "pure" way. I think the authors are quite aware of the relationship between these techniques and mutable state! I imagine it's similar for other canonical functional programming texts. Besides the "pure" funct…
> If you read through the Big Red Book
This is a thoughtful response, but I can't help but chuckle at a response that starts with, just read this book!.