Re: Iterating over buffer lines

[Platon Pronko]

On 2023-06-17 11:28, 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)
>              (forward-line)))))
>
> (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."
>    ........

The code you pasted doesn't seem to work, for example because 
some-chosen-function doesn't exist. So I have trouble understanding what your 
problem is - is the pasted code fragment the example of duplication, or your 
approach to reducing duplication in code that I don't see?

If it's example of duplication (between my-paste-corrected-spacing and some other similar 
functions), then it looks like the duplication is minimal - function name, docstring, and 
underlying function are different. So actual duplication is 2-3 lines - `(&optional 
field-num beg end)`, `(interactive "*p\nr")`, and `my-act-on-region-by-line` parts. 
You can create a macro to reduce that duplication even further, but it seems that we are 
hitting diminishing returns here.

If the code as shown is already an attempt to reduce duplication then it looks 
like you are almost there - you just need to use `(apply some-function)` to 
call the function that you pass to my-act-on-region-by-line.