Capturing output scheme when executing a code block in org-mode

Question

I cannot find a way to intercept the output when I evaluate a scheme code block as below (I'm trying with Geiser):

#+NAME: test
#+BEGIN_SRC scheme :session sicp :lexical t :results output verbatim replace
(define a (list 2 3 4))
(set-car! a 9)
a
#+END_SRC

#+RESULTS: test
: Geiser Interpreter produced no output

This seems to not be possible with Geiser at all as answered on this other question

Is there's another scheme mode that can support my use case?

I just want to get the output from a scheme REPL as in:

#+NAME: test
#+BEGIN_SRC scheme :session sicp :lexical t :results output verbatim replace
(define a (list 2 3 4))
(set-car! a 9)
a
#+END_SRC

#+RESULTS: test
(9 3 4)

The software versions I'm using are:

• GNU Emacs 28.1
• Doom 3.0-dev (can't find a better version than the SHA1 commit 7a30582505)
• org 9.6
• chez scheme 9.5.8

Answer 1

Find the path of ob-scheme.el, for me that is

~/.emacs.d/.local/straight/repos/org/lisp/ob-scheme.el

and then in function org-babel-scheme-execute-with-geiser, change geiser-eval-region to geiser-eval-region/wait, which will wait for the evaluation to finish

        ;;(let ((ret (geiser-eval-region (point-min) (point-max))))
        (let ((ret (geiser-eval-region/wait (point-min) (point-max))))

Finally, press C-M-x to eval the function, and the Geiser worked.

Answer 2

Either use :results value, not :results output, in the code block header, or keep :results output and use (princ a) rather than a (or whatever the equivalent of Elisp's princ is in Scheme).