On Fri, Jun 16, 2023 at 10:28:45PM -0500, Joshua Lambert wrote:
> OK. See below. I'm trying to avoid reusing most of the code in
> function my-act-on-region-by-line. There are multiple functions that
> correct data errors in a csv file and I want to be able to
> interactively run one of those corrections at a time. The resulting
> string will be inserted at the beginning of each line. That all works,
> I'm just trying not to have so much code repetition.
> 
> (defun my-act-on-region-by-line (some-function &optional beg end)
>   "Perform a function on the current line or each line of the region.
> Each SOME-FUNCTION must return a string."
>   (let ((beg2 (if (region-active-p)
>                         beg
>                       (line-beginning-position)))
>           (end2 (if (region-active-p)
>                          end
>                       (line-end-position))))
>     (save-excursion
>       (save-restriction
>          (narrow-to-region beg2 end2)
>          (goto-char (point-min))
>          (while (not (eobp))
>             (goto-char (line-beginning-position))
>             (insert some-chosen-function) ;; Inserts text after a
> function transforms it.
>             (insert my-separator)

The above means that you are inserting stuff at the beginning of the
current line, right?

>             (forward-line)))))

... and this assumes that your `some-chosen-function' doesn't mess
"too much" with point.

> 
> (defun my-paste-corrected-spacing (&optional field-num beg end)
>   "Correct spacing in a string and paste it at the beginning of a line.
> Interactively, BEG and END are the region."
>   (interactive "*p\nr")
>   (my-act-on-region-by-line (some-function-to-correct-spacing field-num)
>    beg
>    end))
> 
> (defun some-function-to-correct-spacing (field-num)
>   "Function that creates a correctly spaced string."
>   ........

I can't /see/ it, but I have a hunch that this function expects
to /replace/ the line by something else. The was it is called
above, its result is /inserted/ in front of the line in question,
right?

Perhaps it's clear to you, but if yes, it doesn't come across:
what is the exact interface between your outer function and
the one called by it?

I.e.: do you need to (save-excursion ...) around `some-chosen-function'?
What do you do with its result? That kind of things.

Cheers
-- 
t