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[#200] Define setters for -first-item and -last-item
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Matus Goljer committed Nov 8, 2016
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Expand Up @@ -578,11 +578,15 @@ Alias: `-any'"
\(fn LIST)")

(gv-define-simple-setter -first-item setcar)

(defun -last-item (list)
"Return the last item of LIST, or nil on an empty list."
(declare (pure t) (side-effect-free t))
(car (last list)))

(gv-define-setter -last-item (val x) `(setcar (last ,x) ,val))

(defun -butlast (list)
"Return a list of all items in list except for the last."
;; no alias as we don't want magic optional argument
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6 comments on commit bcc74b5

@Wilfred
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@Wilfred Wilfred commented on bcc74b5 Nov 8, 2016

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Thanks :)

@Wilfred
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@Wilfred Wilfred commented on bcc74b5 Nov 8, 2016 •
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Hm, looks like this doesn't work on Emacs 23 -- it's broken the tests.

@Fuco1
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@Fuco1 Fuco1 commented on bcc74b5 Nov 9, 2016

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Yes I've noticed too :( Do you know a fix? Apparently gv did not exist back then. But it's not a big deal as we'll be dropping emacs 23 tests soon (as per #195)

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@Wilfred Wilfred commented on bcc74b5 Nov 9, 2016

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I believe there was equivalent functionality in Emacs 23, which we could use. Alternatively, why not just wrap in a (when (boundp 'gv-define-setter') ...) and treat this as an extra feature for recent Emacsen?

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@Fuco1 Fuco1 commented on bcc74b5 Nov 10, 2016

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Then we would also need to guard tests and there it can be messy. If you know how to make this work in e23 I'd rather have that added.

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@Wilfred Wilfred commented on bcc74b5 Nov 12, 2016 •
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I think it's define-setf-expander on Emacs 23 (which works on recent Emacsen too), or defsetf. I'm struggling: Emacs 23 segfaults during compile on my Arch Linux box, and the EVM binaries depend on versions of libtinfo which aren't compatible with Arch Linux's default ncurses install.

IIUC, I think this could be written:

(defsetf -last-item (lst) (v) `(setcar (last ,lst) ,v))

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