Why is *print-circle* set to T by default? WAS: grinding, etc.

I don't know why *print-circle* is set to T by default in Maxima -- it makes
human reading of printed sexpressions much harder, even when there *are*
repeated subexpressions -- see examples below.   Admittedly this makes life
easier for sophisticated users who want to look at assume's data structures
(often found in symbol property lists), but it makes this more complicated
for the beginner who simply wants to see what the Lisp representation of a
Maxima expression is.

You should probably set *print-circle* to nil, unless you're planning to be
creating circular expressions (which are almost never appropriate in Maxima
expressions).

(x+1)^3                  <<< Maxima linear form

((MEXPT SIMP) ((MPLUS SIMP) 1 $X) 3)         <<< Lisp print with
*print-circle* = NIL

((MEXPT . #0=(SIMP)) ((MPLUS . #0#) 1 $X) 3)    <<< Lisp print with
*print-circle* = T

rat((x+1)^3)

((MRAT SIMP ($X) (#:X34080)) (#:X34080 3 1 2 3 1 3 0 1) . 1)

((MRAT SIMP ($X) (#0=#:X34080)) (#0# 3 1 2 3 1 3 0 1) . 1)

3*cos(x)^2*sin(x)-sin(x)^3

((MPLUS SIMP)
 ((MTIMES SIMP) 3 ((MEXPT SIMP) ((%COS SIMP) $X) 2) ((%SIN SIMP) $X))
 ((MTIMES SIMP) -1 ((MEXPT SIMP) ((%SIN SIMP) $X) 3)))

((MPLUS . #0=(SIMP))
 (#1=(MTIMES . #0#) 3 (#2=(MEXPT . #0#) ((%COS . #3=(SIMP)) $X) 2)
  #4=((%SIN . #3#) $X))
 (#1# -1 (#2# #4# 3)))

The main reason to use *print-circle* in Maxima is probably when looking at
the property lists of atoms which have 'assume' (+LABS) properties, which
use a circular Lisp representation.  It's unfortunate that Common Lisp
doesn't support some version of *print-circle* which does not use the #0=
syntax for common subexpressions which are *not* circular (I know, it's
slightly harder to implement, but...).

              -s

On Wed, Feb 9, 2011 at 04:34, Michel Talon <talon at lpthe.jussieu.fr> wrote:

> Hello,
>
> i am trying to write a grind variant to convert expressions so that they
> can
> be embedded in Gnu GMP programs. In the course of doing that, i have, of
> course, consulted forta.lisp, grind.lisp and mactex.lisp, but i see that
> some expressions are of the following form:
> niobe% maxima
> (%i1) x:y*(z+t^2)$
>
> (%i2) :lisp $X
>
> ((MTIMES . #1=(SIMP)) $Y ((MPLUS . #1#) ((MEXPT . #1#) $T 2) $Z))
>
> I am puzzled by the #1=(SIMP) ... #1#
> I suppose that #1 has to be replaced by SIMP but would someone be kind
> enough to explain how this syntax can be understood from lisp?
>
> Well, grind.lisp is not the most obvious thing to understand, i see
> that prof Fateman has lifted some parts to texmacs.lisp and added some
> comments, but does someone know what msize is supposed to do? I am puzzled
> by such stuff:
> (%i2) :lisp (msize $X nil nil 'mparen 'mparen)
>
> (9 (1 y) (8 (3 * ( z) (5 (2 + t) (3 ^ 2 )))))
>
> From Fateman's comments i see that in
> defun msize (x l r lop rop)
> l and r are supposed to be stuff at the left and right of x, while
> lop and rop are left and right "parenthesis", here true parenthesis,
> but if somebody remembers what is this left and right stuff, and what
> these numbers 9 8 etc. mean, i would be grateful.
>
> By the way, at first sight, 9 is the total number of characters in the
> expansion of x, in (1 y) y has 1 character, in (8 ( ...)) there are 8
> characters after the *, but at (3 * i don't understand precisely ...
>
> Of course i suppose the aim is to be able to cut long lines by counting
> characters but how exactly?
>
> Thanks a lot
>
> --
> Michel Talon
>
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