3 ms·

Wow that is a great description of awful design choices. The purpose of SETF is avoiding learning the language?

• chmod775 2y ago
  Language features are superseded by better ones all the time. Nobody gets language design correct on the first try, especially when requirements change over time and by application. If you look at the history of languages like JS or B/C/etc. you better strap in for a crazy ride.
• Zambyte 2y ago
  The purpose is to avoid learning a large vocabulary in favor of a smaller, more general vocabulary. That is abstraction, and it's a feature of the language, so you can't learn it while avoiding learning the language.
• smegsicle 2y ago
  the purpose of setf is to provide an intuitive, powerful, extensible, and simple to use abstraction for an extremely common operation without introducing any new syntax
• kazinator 2y ago
  You should still know about the rplacd function. You can map over it. E.g., delete all middle conses of an assoc list, gluing the first and last one together: [1]> (reduce #'rplacd (list (cons 'a 1))) (A . 1) [2]> (reduce #'rplacd (list (cons 'a 1) (cons 'b 2))) (A B . 2) [3]> (reduce #'rplacd (list (cons 'a 1) '(cons 'b 2) (cons 'c 3) (cons 'd 4))) (A D . 4) If someone finds an application for this, drop me a PM. :) New people learning Common Lisp don't need to know about rplacd, or not right away. Firstly, destructive manipulation of lists should be deemphasized; it is an advanced topic in itself which can produce bugs. People who advance to system level work in Lisp, like doing work on implementations, will have to know it. rplacd can appear in code that cannot use setf, because it is processed before setf has been boostrapped. You will run across rplacd in other people's code even if you don't use it yourself; so if you go beyond just writing programs for yourself into collaboration and maintenance of existing code, you can't avoid knowing about it. If you ever have to debug the code produced by (setf (cdr place) ...), you will likely see rplaca or a similar function.
• bsder 2y ago
  The point is to make accessing a data structure somewhat "generic". I only have to change the "(car a)" to "(superdupercar a)" and the "setf" propagates the changes along. This is especially important inside macros. It is also the reason why Lisps can feel so icky. This is a huge hunk of "macro magic" that can be damn near impenetrable when something goes wrong. The longer I'm at this the more I'm convinced that macros are the reason why Lisp lost. Even if I concede that macros are hugely powerful, every language that leans into something equivalent to macros winds up with inscrutable errors, debugging issues and/or excessive compile times.
  • kazinator 2y ago
    If you change (car a) to (superdupercar a), then (setf (superdupercar a) x) no longer works. You have to program the generalized place system of Common Lisp to recognize (superduper ...) as a place, and define what that means; then all is well. It could be as simple as (defsetf superdupercar superduperrplaca) If you have a function (superduperrplaca a x).
  • deleted 2y ago
    [deleted]
• pkhuong 2y ago
  The purpose of the place system is to support side-effectful macros where programmers don't have to repeat what they mean n times.