[tikhonj]

Design-wise, Emacs is less an editor with an API and more a set of core editing concepts (buffers, strings with properties... etc) embedded into a flexible language. The core concepts have a native implementation that's hard to change, but they're simple and flexible enough that you can put them together to do all kinds of text-editory (or even not-so-text-editory) things.

Everything on top of the core is written in an open style, with Lispy features that make it easy to hook into or modify anything. Adding a small feature to Emacs doesn't feel like calling APIs from an existing application, it feels either like writing my own code with text editor stuff available as a library or, alternatively, like tapping into and fiddling directly with existing code in the system.

This way of seeing Emacs explains both why it's so flexible and why certain things (better performance on long lines, concurrency) are so difficult: you can express a lot using the core concepts and you can easily change other code that's expressed with these concepts, but making fundamental changes to the core itself is far more difficult. Partly it's more difficult because it's an old C codebase pretty separate from the Lisp world but, more importantly, it's difficult because substantial changes to the building blocks will change or break existing code in ways that are hard to control or predict. It's the very flexibility on top of the core that makes the core itself hard to change, since the higher-level Lisp code is using the core concepts in all kinds of ways.

[vintermann]

> it's difficult because substantial changes to the building blocks will change or break existing code in ways that are hard to control or predict.

This is a sign that emacs has too much extensibility (or, to be more accurate: too little isolation). It's been observed before that emacs really is the antithesis of the alleged Unix philosophy of "doing one thing and doing it well". It is an inner platform.

[scombridae]

Well, it's a doulbe-edged sword.

Causally linking glaring deficiencies (long lines, concurrency) to overriding virtues (extensibility) is a weak but common snow job aimed at emacs's critics who know nothing of emacs's internals. For this emacs critic who knows quite a bit about emacs's internals, I call you out.

There's only one reason for emacs's many wtf frailties. No one's paying to fix them.