AW <alexander.willand@t-online.de> writes:

> Dear all,
>
> I dare to ask this slightly off-topic question, because of the discussion
> about pdf-tools a day ago.
>
> I installed pdf-tools (https://github.com/politza/pdf-tools). It is a _lot_
> faster than doc-view. Many thanks to Matt Price
> (http://matt.hackinghistory.ca/2015/11/11/note-taking-with-pdf-tools/) I got
> it working with orgmode.
>
> But I'd like to use it to display my PDFs I produce with LaTeX (Emacs, AUCTeX)
> as well.
>
> The trouble is the automagic reloading of the PDF every time it get's changed
> on disk. Okular does this, but pdf-tools need some kind of invitation?!
>
> From here https://github.com/politza/pdf-tools/issues/128
> is this setup for .emacs:
>
> ============= 8< ==============
>
>
> (pdf-tools-install)
> (load "pdf-tools")
> (setq TeX-view-program-selection '((output-dvi "Okular")
> (output-pdf "PDF Tools") ;;
> ))
>
> (require 'subr-x)
> (defun th/pdf-view-revert-buffer-maybe (file)
> (when-let ((buf (find-buffer-visiting file)))
> (with-current-buffer buf
> (when (derived-mode-p 'pdf-view-mode)
> (pdf-view-revert-buffer nil t)))))
>
> (add-hook 'TeX-after-TeX-LaTeX-command-finished-hook
>  #'th/pdf-view-revert-buffer-maybe)
>
>
> ================ >8 ============
>
> If I compile a *.tex file again, I get the error
>
> "error in process sentinel: Symbol's function definition is void: when-let"
>
> ...and the PDF won't get updated.
>

So when-let is not defined above, and it is not defined by emacs, so you
got to get the definition from somewhere. Go back to the link and you'll
see further down that the OP complains about the same thing. The
solution seems to be

   (require 'subr-x)

> Can anybody help me to get a working setup? Really, this libpoppler behind
> pdf-tools is such a lot faster, it reminds me on xpdf.
>

That's because libpoppler is essentially a library version of xpdf:

$ yum info poppler
Loaded plugins: auto-update-debuginfo, copr, etckeeper, langpacks
Installed Packages
Name        : poppler
Arch        : x86_64
Version     : 0.26.2
Release     : 9.fc21
Size        : 2.6 M
Repo        : installed
Summary     : PDF rendering library
URL         : http://poppler.freedesktop.org/
License     : (GPLv2 or GPLv3) and GPLv2+ and LGPLv2+ and MIT
Description : Poppler, a PDF rendering library, is a fork of the xpdf PDF
            : viewer developed by Derek Noonburg of Glyph and Cog, LLC.

--
Nick