ob-calc duplicate stack-element issue

[Heiko Schmidt]

Hi there,

the following org snippet is describing my issue.

Thanks in advance,
Heiko

* TODO post problem report about ob-calc duplicate stack-element issue
    :LOGBOOK:
    - State "TODO"       from              [2020-03-15 Sun 09:19]
    :END:

- I want to use ob-calc to do some "literate calculation" with the
  purpose to document what I thought at the time I wrote it.

- problem: When evaluating the calc snippets the top of stack element
  is dropped. Because every "begin/end_src calc" block drops the top
  of stack, one can't reuse the result in following blocks.

- although without expecting any effect here is some version
  information:

    - emacs version: GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version
    3.14.5) of 2017-09-12 on hullmann, modified by Debian

    - org-version:   9.2

** what I'd like to be able

Number of cars (PKW) in germany:

#+begin_src calc :exports both
45e6
#+end_src

#+RESULTS:
: 45000000.

Yearly mileage in [km/y]

#+begin_src calc :exports both
15000
#+end_src

#+RESULTS:
: 15000

Calculate amount of complete km per year

#+begin_src calc :exports both
'*
#+end_src

#+RESULTS:
: 675000000000.

** the problem I'm facing and the nearly working work-around

- problem: babel removes the resulting top stack element from the
  stack

- tried solution: duplicate the last stack-element on evaluation with
  "' " (emulate <space> press to duplicate the top element of the
  stack in calc)

- side effect: I normally delete trailing whitespace in my files - so
  entering "' " is a dangerous workaround

- I tried to local-set-key the § key to calc-enter which I thought
  should enable a command "'§" to duplicate the top of stack. On
  evaluation this resulted in an error "byte-code: Wrong type
  argument: number-or-marker-p, nil"


Number of cars (PKW) in germany:

#+begin_src calc :exports both
45e6
'<space>
#+end_src

#+RESULTS:
: 45000000.

Yearly mileage in [km/y]

#+begin_src calc :exports both
15000
'<space>
#+end_src

#+RESULTS:
: 15000

Calculate amount of complete km per year

#+begin_src calc :exports both
'*
'<space>
#+end_src

#+RESULTS:
: 675000000000.

** hope for a solution or work around from the community

- preferred: Is there a way to leave the top of stack from one snippet
  to the next (which I don't know)?
- alternative: Is there a way to duplicate the top of stack element
  between begin/end_src calc blocks?
- any advice is appreciated.