- My values represent runs of characters in the document.
- Inserts in the tree may split a run.
- Runs have a size - 0 if the run is marked as deleted or the number of characters otherwise. The size changes as we process edits
- Every inserted character has an ID. I need to be able to look up any run by its ID, and then edit it. (Including querying the run’s current position in the tree and editing the run’s size).
It’s an interesting data structure problem, and it took a few weeks to have a good solution (and a few weeks more later rewriting it in safe rust & improving performance in the process).
I love this stuff. I think it’s pretty rare to find a reason to code your own collection types these days, but it certainly comes up from time to time!
Absolutely! That is one of the places you want to use that style of programming. As the base classes and built in structs do not really cover it yet.
Also as a counterpoint sometimes the built in ones have some very interesting degenerate cases. I had one in an old library that basically doubled its memory footprint every time you exceeded its buffer. That was a point to change it to be a fixed allocation or something else. If i had no idea of the fundamentals I would have been totally in the weeds and no idea why it was doing it.
Seems like the glaring exception to the rule!
(write-string (cdr '(write-string "hello-world"))) also has to work, so it's pretty easy to materialize that semantics at any point.
Nope; it has linked list syntax (that certainly isn't ignored even by very good compilers). Syntax isn't semantics.
The semantics is that a function write-string is called, with a string as its argument.
The second expression has linked list processing in its semantics because you stuck in a cdr, as well as a quote which makes a piece of the program available as run-time list datum. (This is semantics that could be easily optimized away in the executable form, but I would say that it has linked list processing in its abstract semantics.)
We're looking at the same string and seeing different things. You're seeing `(write-string "hello world")` as a program, I'm seeing it as an expression.
It has linked list semantics, which you can preserve until runtime like this `'(write-string "hello world")`. Note that I didn't change the string, I changed its context. If the original were living in a string, and you called read on it, it would become a linked list. If you called eval on that list, it would become a function call. This is basic stuff which I'm well aware you know, so I'm not sure what all the quibbling is about.
You literally need a linked list to write a program in a language in which the code becomes linked lists. And you're going to have a bad time writing Lisp if you don't get the hang of cons cells, early and often.
Is "code is data" true, or false? You're trying to have it both ways here.
The "large number of programmers who have learned about linked lists but haven't run into many cases where they needed them in the world world" include approximately zero programmers who have wielded Lisp in anger, is my point. I thought that was pretty clear from context, but I guess not.
You're also likely provoking list manipulation by running C hello world. The C grammar has lists, like lists of parameter declarators in a function, or argument expressions in a function call.
By the time you've compiled your C program, you've likely "used", lists, trees and hash tables.
Classic line-numbered BASIC interpreters stored the lines as a linked list. For instance in
10 PRINT "Hello"
20 GOTO 10
So in addition to not being able to write C hello without linked lists, the same holds for BASIC.
The way you present your idea about Lisp is harmful because it is likely to be misinterpreted and become misinformation in the eyes of those who not so well informed.
The Lisp community still has to deal with nonsense like that the execution of Lisp programs is slow because linked lists are continuously being traversed, or that the only data structure is a list.
Think about how you might be playing into that. What do you think it looks like when you say that you can't write a hello world, without using linked lists.
SBCL:
* (defun hello-world () (write-string "hello world"))
HELLO-WORLD
* (disassemble #'hello-world)
; disassembly for HELLO-WORLD
; Size: 36 bytes. Origin: #x100311C85C ; HELLO-WORLD
; 5C: AA0A40F9 LDR R0, [THREAD, #16] ; binding-stack-pointer
; 60: 4A0B00F9 STR R0, [CFP, #16]
; 64: EAFDFF58 LDR R0, #x100311C820 ; "hello world"
; 68: 570080D2 MOVZ NARGS, #2
; 6C: 29EC80D2 MOVZ TMP, #1889
; 70: BE6B69F8 LDR LR, [NULL, TMP] ; WRITE-STRING
; 74: DE130091 ADD LR, LR, #4
; 78: C0031FD6 BR LR
; 7C: E00120D4 BRK #15 ; Invalid argument count trap