[BUG] Inconsistent global/local :var assignments in ob-* for lisps and non-lisps (was: org-babel guile source block bug in handling multiple values)

[Ihor Radchenko]

Zelphir Kaltstahl <zelphirkaltstahl@posteo.de> writes:

> I am not sure (let ...) is a correct wrapper for noweb included source 
> blocks. 
> What, if I write a (define ...) in my source block and want to use that 
> source 
> block via noweb in another source block? Expected behavior I think would be 
> to 
> be able to access those variables in other source blocks, since they are 
> defined 
> on a top level in an earlier source block, but if they are wrapped in a (let 
> ...), that would make them only available in the (let ...)? It seems to me, 
> that 
> the simple wrapping with a (let ...) might not be the right thing to do. 
> Testing 
> that:
>
> ~~~~START~~~~
> #+name: scheme-defs
> #+begin_src scheme :eval query-export :noweb strip-export :session myguile 
> :results output replace drawer :var x=1 :var y=2
> (define a x)
> (define b y)
> #+end_src
>
> #+name: scheme-time
> #+begin_src scheme :eval query-export :noweb strip-export :session myguile 
> :results output replace drawer
> <<scheme-defs>>
> (simple-format #t "~a ~a\n" a b)
> #+end_src
> ~~~~~END~~~~~
>
> Indeed, that also does not work.

I just checked ob-C, ob-shell, ob-emacs-lisp, and ob-clojure.
Non-lisps appear to assign the values globally.
In contrast, all the lisp babel backends are using let-bindings.

Considering the existing inconsistency, and the raised bug I'd be in
favor of making variable assignments global in all the lisp babel
backends.

The only possible exception is ob-emacs-lisp. Executing elisp code is
done in current Elisp session and thus using global variable assignments
may be tricky. Unless we juggle with multiple obarrays.

> I guess I did never hit this problem earlier, because I "oursourced" my 
> imports 
> and in imports I do not need any :var header arguments.
>
> I've asked on the Guile IRC channel and something interesting is the case 
> here 
> (thanks for clearing it up flatwhatson!) and I understand it as follows:
>
> Imports inside (let ...) work. It is just that let-values is a macro and 
> macros 
> are expanded before execution time. However, Guile gets to the body of the 
> wrapping (let ...) at execution time. That means, that when Guile gets to 
> evaluate the body of the let, it does not expand the let-values, because it 
> is 
> already at execution time and no longer at macro expansion time. The import 
> might import the let-values form, or might not, but it is already too late to 
> expand the (let-values ...).

So, apparently using `let' is not universally safe in Guile.

> OK, the question is though, whether org should wrap anything in a (let ...) 
> at 
> all. During discussion on the Guile IRC, some points against let-wrapping 
> were 
> brought up:
>
> (1) The presence of a :var header argument currently determines, whether the 
> code in the source block is wrapped with a (let ...). One argument for that 
> was, 
> that this way the variables do not leak. But this also decides, whether other 
> things leak. For example (import ...) or (define ...). Should :var decide, 
> whether bindings created with (define ...) are visible in other source blocks 
> including the source block with the :var header arguments? It seems like a 
> responsibility :var should not have and definitely is unexpected for the user.

This is something Guile-specific. In Elisp, let-binding still allows
`defun' or `defvar'.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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