Re: RFC: make maphash return a list

[Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com>]

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What is easier to read... that would probably be a matter of taste.
Granted, it was a bad example. If find the "nested mapcar" approach easier
to read (though probably not with unmodified indentation rules) when
single-element functions with mapcar and functions operating on lists
alternate, e.g.

  (append
    (mapcar 'function-that-returns-list
      (function-taking-and-returning-lists
        (mapcar 'something-else input-list))))

Basically I find emacs lisp that contains mostly of such "diagonals" the
easiest to read in terms of structure (but this goes beyond the original
topic and to some degree more into indentation conventions).

But subjectively the actually important point is the avoidance of
variables, whose value changes after declaration (preserving a 1-on-1
relation between name and value during execution of the function). Then I
have to find only the let form that declared the variable in order to know
its intended contents rather than scan through the whole function. With
maphash and similiar that style (would that be functional style?) is not
possible.

That said, I have just written a little private-use library for such
things. Bottomline, if I want to program more functionally it doesn't even
take much bending of elisp to do so.

kind regards, Klaus


2013/6/18 Davis Herring <herring@lanl.gov>

> >   (let (mapped-hash) (maphash (lambda (k v) (push (return-something k
> >     v) mapped-hash))) (mapcar 'modification-2 (mapcar 'modification-1
> >     mapped-hash)))
>
> For what it's worth, you can at least here write
>
> (let (mapped-hash)
>   (maphash
>    (lambda (k v)
>      (push (modification-2 (modification-1 (return-something k v)))
>            mapped-hash))
>    hash)
>   mapped-hash)
>
> (so long as the various functions are pure enough to allow the
> reordering).  Indentation makes it longer than
>
> (let (mapped-hash)
>   (maphash (lambda (k v) (push (return-something k v) mapped-hash))
>            hash)
>   (mapcar 'modification-2 (mapcar 'modification-1 mapped-hash)))
>
> (which in 80 columns can even have the tiny line appended to the
> previous), but I think it is conceptually simpler.
>
> Davis
>
> --
> This product is sold by volume, not by mass.  If it appears too dense or
> too sparse, it is because mass-energy conversion has occurred during
> shipping.
>

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