Re: [Feature Request] Add Zsh-style range and list iteration syntax to Eshell

[Jim Porter]

On 12/4/2024 9:15 AM, the_wurfkreuz via Emacs development discussions. 
wrote:
> Zsh has an ability to quickly iterate over ranges and lists like this:
>
> touch file{1,3}
>
> creates: file1, file3

Thanks for the suggestion. However, I'd prefer not to add even more 
meanings for punctuation to Eshell; it's pretty complicated as it is, 
since it tries to combine both shell-like syntax with Lisp-like syntax. 
(I've been maintaining Eshell for the last couple years and still 
haven't fixed all the corner cases in the existing syntax.)

In this case though, I think you could make a helper function that gets 
you a fair amount of the way there:

  (defun eshell/expand (fmt list)
    (mapcar (lambda (i) (format fmt i)) list))

Then in Eshell:

  touch $@{expand file%s `(1 3)}

It's a bit more typing than Zsh, but less than writing a for loop.

You could also write an external Eshell module that parses syntax like 
this. em-pred.el could probably serve as some inspiration, as well as 
some examples of how it's tricky to get this right (for example, 
em-pred.el only supports predicates at the *end* of a word).

You might also be able to add a custom argument modifier that works 
somewhat like "expand" above. See 'eshell-modifier-alist'.

> It would be handy to have something similar in eshell instead of 
> explicitly writing a loop:
>
> for i in (number-sequence 1 5) {
>      touch (format "file%d" i)
> }

As of Emacs 31, you could shorten this to:

  for i in 1..5 { touch (format "file%d" i) }