Re: dash.el [was: Re: Imports / inclusion of s.el into Emacs]

[Stefan Monnier]

> there I think I just want flatten to exist already.

His point was: it's rare to need exactly `flatten` (which BTW is called
`flatten-tree` since Emacs-27 ;-).
AFAIK in most cases what you really want is something along the lines of
(apply #'append X), i.e. a "one-level flatten".

As its name implies, `flatten-tree` really operates on a tree, but it's
very rare to represent trees in Elisp in such a way that all non-cons
cells are elements of the tree, so `flatten-tree` rarely does something
meaningful on a tree.

But yes, there are several cases where you may happen to know that
`flatten-tree` will work because it won't have the opportunity to go
deeper than the first level.  I.e. you have a "list of lists of strings"
or a "list of either strings or lists of strings", so you won't see the
difference between `flatten-tree` and a hypothetical one-level flatten.


        Stefan