"Eric Schulte" <address@hidden> writes:
Vincent Beffara <address@hidden> writes:
Hi,
(and it would be excellent to allow for a code block as a
preamble,
instead of a string in the header or as an alternative, because
preambles once they are allowed tend to grow uncontrollably ;->)
This is currently possible using the `sbe' function. Arbitrary
emacs
lisp can be placed inside of header arguments, and the `sbe' take
the
name of a code block and returns its result.
This makes me think of another good use of the sbe ("src block eval")
function. I'm often seeing Org documents with a src block like this,
#+source: essential-document-config
#+begin_src emacs-lisp
;; some essential document-specific configuration
#+end_src
and some instructions saying something like "To use this document,
first
evaluate this code block".
This can be automated by using sbe in a local variables line at the
end
of the Org file:
# Local variables:
# eval:(sbe "essential-document-config")
# End:
When the file is first opened, Emacs will evaluate the set-up blocks
(after asking for confirmation).
This isn't restricted to configuration of Emacs variables with
emacs-lisp blocks; eval lines could reference blocks in any language,
for example to start an ESS session and run some preparatory code,
etc,
e.g.
#+source: document-config
#+begin_src emacs-lisp
(set (make-local-variable 'org-edit-src-content-indentation) 0)
#+end_src
#+source: start-ess
#+begin_src R :session *R session*
a <- 1
#+end_src
# Local variables:
# eval:(sbe "document-config")
# eval:(sbe "start-ess")
# End:
Dan
Very cool ! That does all I want, thanks for the info. For multi-
line it
is a bit heavy to write, with lots of \n and preamble .= "lskjd",
but I
can live with that. Unless there is a way already to write something
like this ?
#+source: my-preamble
#+begin_src python :return preamble
# -*- coding: utf-8 -*-"
import os,sys,whatever
#+end_src
#+begin_src python :preamble (org-babel-get-and-expand-source-code-
body my-preamble) :return s
s = "é"
#+end_src
There is org-babel-get-src-block-info but it looks at the block
around
(point), not by name ... so I guess it would not be too hard to
write
the extraction method, but it might be somewhere in the code
already.
Yes, the following uses an internal Babel function, but is probably
much
simpler
#+results: my-preamble
: # -*- coding: utf-8 -*-
: import os,sys,whatever
#+begin_src python :preamble (org-babel-ref-resolve "my-
preamble") :return s
s = ""
#+end_src
Note that as written this will return the following python error
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
ImportError: No module named whatever
One naive question : why is the code path different for tangling
and
evaluation ? One would think that a natural way for evaluation
would be
to tangle the current block (plus included noweb stuff etc) into a
temporary file and eval that file ... and that would enable
shebang for
evaluation as well. There must be something I am missing here.
Tangling works for *any* programming language, even those which
have yet
to be created and have no explicit Emacs or Org-mode support,
this is
because on tangling the code block is simply treated as text.
As far as I understood from testing, tangling does adapt to the
language
(at least to implement :var in a suitable way), so I was under the
impression that evaluating could be implemented as some kind of
wrapping
around the tangled output - and obviously the wrapping would have
to be
language-specific even if for the most part the tanglong is not.
Yes, some language specific features (e.g. variable expansion) can be
used by the tangling mechanisms if such features are defined for the
language in question, however tangling can be done in the absence
of any
language specific features and thus works for any arbitrary language.
That shebang and preamble should remain separate for the other
reasons
mentioned in my previous email.
I am just discovering all of this, sorry if I have horrible
misconceptions about the thing ...
No problem, it is a fairly (but I don't think overly) complex system.
Regards,
/v
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