[loup-vaillant]

So do I. I prefer to type out `=` three times, for a simple reason: while not being more verbose than the `setf` example (3 additional tokens in both examples), it makes all 3 lines the same, which is more regular.

We could make all 3 lines the same with `setf`, but that would be a bit more verbose:

  (setf x 10)
  (setf y 20)
  (setf z 30)

In a program that heavily use the assignment statement, I vote for the shorter form, `=`.

[kazinator]

It is absolutely more verbose. The Lisp form can store N constants into N variables in 2N+3 tokens: two parentheses, plus the variables and constants and one symbol. Assignment statements require 3N tokens: N vars, N constants, N assignment operators. That's assuming they don't need some mandatory separator or terminator like a semicolon. We break even when N = 3. For N > 3, 2N+3 < 3N.

Anyway, this is hardly the main point of the article (and probably detracts from it).

[loup-vaillant]

Indeed, my main point is not verbosity —it's regularity. I'd rather repeat `setf` in most cases in the name of regularity. That way we spot the semantic difference between lines more easily.

You'd have to use the assignment heavily to justify implementing the `=` syntax, which is barely prettier than the regular `setf` syntax. Plus, you'd probably have to add some annotation anyway, partially defeating the point:

  (assign
    x = 10
    y = 20
    z = 30)

[kazinator]

If you repeat setf, you may need a progn to make it one expression. And parallel assignment is off the table without temporary variables:

  (if condition
    (psetf a c b a c b)
    (psetf a b c a b c))

:)

P.S. of course I know rotatef would be better here.

[PrettyButUgly]

I'm not much for Common Lisp, but I do think Scheme is the prettiest language in which people write ugly code. As such, while I am sympathetic to the virtues of s-expressions, this example is not going to win any hearts or minds. I don't much care for Python's performance or newer features, but your snippet screams for a comparison:

    if condition:
        a, b, c = c, a, b
        a, c, b = b, a, c

That really seems much more clear than the gymnastics my mind has to do manually pairing the assignments inside of psetf. I won't argue that it's objectively better syntax, but I still think it is.

[qwertyuiop924]

Well...

  (define-syntax assign-group!
    (ir-macro-transformer
      (lambda (x i c)
        (let ((vars (cadr x))
              (vals (caddr x)))
          `(let ,(map (lambda (var val) '(var val)) vars vals)
             ,@(map (lambda (var) 
                      `(set! ,(i var) ,var)) vars))))))

Mind, I haven't tested this, because I don't have CHICKEN Scheme (the dialect this is written in) in front of me, and I may not have matched all the parens on the end, but it should work like this:

  (assign-group! (a b c) (c a b))

Giving you your nice assigment syntax you wanted.

That's the nice thing about Lisps: if you don't like it, you can change it.

[qwertyuiop924]

There is in fact one error in the above macro: well, I think only one: in the map, (lambda (var val) '(var val)) should be (lambda (var val) (list var val))

[kazinator]

That's why I mentioned rotatef:

   (rotatef a c b) ;; a <-- c <-- b
                   ;; `--->----->-'

[gluggymug]

You forgot "else:"

[PrettyButUgly]

Funny that. In my head, I parsed it as two (odd) statements under one if statement. More like when than if.

[orbifold]

That is why you would typically create a struct, and then assign the whole struct at once. If you are regularly assigning > 20 variables at the same time, something is wrong with the language you are using.

[Avshalom]

on the other hand = is one character, and if it's not a legal character in identifiers then x=1 y=2 z=3 takes 2n characters (setf x 1 y 2 z 3) takes 2n+7 characters (plus however many we're using for the actual identifies and values but those'll be the same between examples)

[kazinator]

Lisp has an = function; so that binding is taken. Symbols in the keyword package are allowed to have function bindings, and so a synonym for setf can be called := (the symbol named "=" in the keyword package).

  [1]> (defmacro := (&rest args) `(setf ,@args))
  :=
  [2]> (defvar a)
  A
  [3]> (:= a 42)
  42
  [4]> a
  42
  [5]> (= a 42)
  T