bug#43995: 27.1; Argument orderd in function parameter of seq-reduce

[Nathan Benedetto Proença]

Good afternoon!

This is not a bug per se, but I was directed here by

https://github.com/NicolasPetton/seq.el

I want to know if there is any guarantee regarding the order of
parameters passed to the FUNCTION argument in seq-reduce.

'C-h f seq-reduce RET' tells me that:

> seq-reduce is an autoloaded compiled Lisp function in ‘seq.el’.
> 
> (seq-reduce FUNCTION SEQUENCE INITIAL-VALUE)
> 
> Reduce the function FUNCTION across SEQUENCE, starting with INITIAL-VALUE.
> 
> Return the result of calling FUNCTION with INITIAL-VALUE and the
> first element of SEQUENCE, then calling FUNCTION with that result and
> the second element of SEQUENCE, then with that result and the third
> element of SEQUENCE, etc.
> 
> If SEQUENCE is empty, return INITIAL-VALUE and FUNCTION is not called.

The wording gave me the impression that the first argument of FUNCTION
is the accumulator, and the second is the element of the SEQUENCE, but I
was not sure.
By inspecting the code, I saw that this was indeed the case.

This mattered because I had a closure as an accumulator, and wanted to
update this closure by iterating over a list whose elements where not
closures.

The example in the Elisp book

https://www.gnu.org/software/emacs/manual/html_node/elisp/Sequence-Functions.html#Sequence-Functions

uses addition, in which this issue does not arise.

If it is a good idea, I could update the docstring and the manual, but I
would need some pointers on how to do it.

Thanks in advance!
Nathan


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