bug#46750: calc defmath let* behaviour surprising, inconsistent, or wrong

[Stephan Neuhaus <stephan.neuhaus@zhaw.ch>]

Dear maintainers

I can't seem to understand the calc documentation, or I may have found a 
bug. You decide :-)

My system

"GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
  of 2019-09-23, modified by Debian"

I'm trying to define a calc function f() for use in org mode. Here is a 
minimal example of what I've tried. It's not the same function, but it 
exhibits the same behaviour. Put this text in a buffer with org mode:

#+BEGIN_SRC emacs-lisp
   (defmath f(x)
     (let* ((m x)
	   (n (+ m 1)))
       n))
#+END_SRC

#+RESULTS:
: calcFunc-f

|   x | y      |
|-----+--------|
| 1.0 | f(1.)  |
| 1.5 | f(1.5) |
| 2.0 | f(2.)  |
| 2.5 | f(2.5) |
| 3.0 | f(3.)  |
| 3.5 | f(3.5) |
| 4.0 | f(4.)  |
| 4.5 | f(4.5) |
| 5.0 | f(5.)  |
#+TBLFM: $2=f($1)

Evaluating the source block (C-c C-c on END_SRC) defines f() 
successfully. Then hitting C-c C-c on the TBLFM line shoud result in the 
y column of the table to be filled with the x column, plus 1, which it 
doesn't.

If I directly evaluate x + 1, it works:

#+BEGIN_SRC emacs-lisp
   (defmath f(x)
     (+ x 1))
#+END_SRC

#+RESULTS:
: calcFunc-f

|   x |   y |
|-----+-----|
| 1.0 |  2. |
| 1.5 | 2.5 |
| 2.0 |  3. |
| 2.5 | 3.5 |
| 3.0 |  4. |
| 3.5 | 4.5 |
| 4.0 |  5. |
| 4.5 | 5.5 |
| 5.0 |  6. |
#+TBLFM: $2=f($1)

It seems to me that the problem is with the let* special form, which 
simply doesn't seem to work. let works:

#+BEGIN_SRC emacs-lisp
   (defmath f(x)
     (let ((n (+ x 2)))
       n))
#+END_SRC

#+RESULTS:
: calcFunc-f

|   x |   y |
|-----+-----|
| 1.0 |  3. |
| 1.5 | 3.5 |
| 2.0 |  4. |
| 2.5 | 4.5 |
| 3.0 |  5. |
| 3.5 | 5.5 |
| 4.0 |  6. |
| 4.5 | 6.5 |
| 5.0 |  7. |
#+TBLFM: $2=f($1)

I couldn't find anything in the documentation that would forbid me from 
using let* in the body of a defmath. I also couldn't find anything that 
would explain this behaviour.  Now I'm not an expert on Lisp, so it's 
entirely possible that I've done something stupid, or missed something 
in the documentation, but I can't find out what it might be.

Thank you very much for Emacs. After several years of using other 
editors, I'm coming back to Emacs and I don't think I'll leave it again. 
Well, except maybe for ed(1). Ed is the standard editor.

Cheers

Stephan

PS: I'm following the instructions in the calc manual for filing a bug. 
There is no mention of a mailing list or a bug tracker for me to sign up 
to, so I'd be grateful if you could answer this email, otherwise I might 
miss requests for more information or the announcement of a resolution.