Clojure’s Approach to Identity and State (2008)

Post by [deleted] » Sat, Jul 13, 2019, 9:13 PM UTC

[deleted] wrote: post #19

stuhood wrote: post #12

Immutability is very helpful, and the connection between values and identity is illuminating. But there have been very important developments in programming languages since this post/page was written: notably, the introduction of "borrow checking" (exemplified by Rust's implementation). Borrow checking has a very significant positive effect on the sustainability of imperative code, which makes the claim that "imperat…

[deleted]

Post by casion » Sat, Jul 13, 2019, 10:33 PM UTC

stuhood wrote: post #21

stingraycharles wrote: post #15

Earlier quoted context omitted.

Borrow checking and immutability solve two different problems. Immutability is about the absence of ownership and state, while borrow checking is a way to manage ownership. One does not replace the other, they coexist solving different problems.

Borrow checking allows even structures that support mutation to be safely (checked by the compiler) treated as immutable, and thus as values. Clojure also recognizes the connection between ownership and mutability in its "transients": https://clojure.org/reference/transients ... compile time borrow checking extends that idea to an entire language.

Post by 6thaccount2 » Sat, Jul 13, 2019, 10:47 PM UTC

agumonkey wrote: post #10

etbebl wrote: post #6

This is interesting. I've tried Clojure, and heard about the idea of avoiding mutable data and using pure functions plenty of times, but imperative/OOP have still always made the most sense to me. When reading this though, something clicked because I've encountered the problem of getting a stable state to read/write without blocking other operations, and dealt with it in C++ in a similar way to Clojure without realiz…

IIUC Rich Hickey probably did just that too, writing ad-hoc version of clojure semantics in cpp before making his own language enforcing this.

Post by [deleted] » Sat, Jul 13, 2019, 11:06 PM UTC

stuhood wrote: post #20

louthy wrote: post #17

Earlier quoted context omitted.

Exactly, it's like the integer 5, nobody owns the number 5, nothing borrows the number 5, it just exists as a value that anything can use (and trust to always be the same). When immutable values (whether it's the number 5 or a record, or whatever) are used with a pure function then the returned value can be essentially a direct replacement for the function invocation, making the operation essentially take zero time (…

> When immutable values (whether it's the number 5 or a record, or whatever) are used with a pure function then the returned value can be essentially a direct replacement for the function invocation, making the operation essentially take zero time (i.e. there aren't intermediate mutation states, locks, or any other coordination). The same can be said of any variable in Rust that is passed to a function via immutable…

Post by 6thaccount2 » Sat, Jul 13, 2019, 11:18 PM UTC

tosh wrote: post #29

6thaccount2 wrote: post #26

Earlier quoted context omitted.

I recall he was big into SBCL, but most IT organizations wanted all code to run on the JVM or CLR. So he had to make a Lisp to run on the JVM and Armed Bear Common Lisp apparently wasn't exactly what he wanted. I want to learn Clojure, but there are definitely some road blocks. I don't have the time for Emacs, it'd be a pain to get a Cursive license (although the cost is extremely reasonable I'd have to do paperwork…

Visual Studio Code, Atom and Vim also have great Clojure support. (edit: might be worth to add editors and IDEs to the Clojure landing page to illustrate that there are many solid options by now) With ClojureScript you can leverage JavaScript runtimes like browsers. The ClojureScript testsuite also passes using the recently released hermes runtime ( https://twitter.com/mfikes/status/1149360258994847745 ) edit: Just w…