[Maxima-discuss] Writing low-level `dim-*' functions

[Eduardo O. <edu...@gm...>]

Hi all, especially Michael and Richard,

this is a continuation of this other thread, from a few days ago,
that was about the data structures used by functions like `dim-%at',
`dim-%integrate', and `dim-$matrix'...

  https://sourceforge.net/p/maxima/mailman/message/59177191/
  https://sourceforge.net/p/maxima/mailman/message/59177280/
  https://sourceforge.net/p/maxima/mailman/message/59177328/

I am still struggling with the basics, but at least I found a nice
way to write my questions... if we run this in a Maxima REPL,

  to_lisp();

    (defun s  (str) (coerce str 'list))
    (defun sr (str) (reverse (coerce str 'list)))
    (defun my-result ()
      `(,@(s "f(x)")
        (D-VBAR 2 1 #\|)
        (0 -1 ,@(sr "x = a"))
        (-5 1 ,@(sr "x = b"))))
    (displa-def $foo dim-$foo)
    (defun dim-$foo (form result)
      (format t "form: ~S~&result: ~S~&" form result)
      (update-heights 2 1)
      (reverse (my-result)))

    (to-maxima)

  foo(3, "4");

We get:

  (%i2) foo(3, "4");
  form: (($FOO SIMP) 3 "4")
  result: ((0 0) #\  #\) #\2 #\o #\% #\()
      |x = b
  f(x)|
      |x = a
  (%i3)

Note that the "f(x)|..." is left aligned, instead of being centered
and preceded by an "(%o2)". That's because the `dim-*' functions
sometimes return with a:

  (return (dimension-function form result)))

and sometimes with just this...

  (return result)))

What does `dimension-function' do? I found it very hard to understand,
to debug with Sly, and to test in other ways...

  Thanks in advance!
    Eduardo Ochs