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

On 2/9/11 10:01 AM, Stavros Macrakis wrote:
> 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.
It was changed sometime in 2009 by Robert.  I guess he was working with
the assume database which apparently has circular structures.

I normally just turn it off now (by hand) when I print the Lisp rep.  I
ought to be able to read them, but I find it rather hard to read.

Ray

>
> 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#) $X))
>  (#1# -1 (#2# #4# 3))) 
>
> The main reason to use *print-circle* in Maxima is probably when
> looking at the property lists of atoms which have 'assume' (+LABS)
> properties, which use a circular Lisp representation.  It's
> unfortunate that Common Lisp doesn't support some version of
> *print-circle* which does not use the #0= syntax for common
> subexpressions which are *not* circular (I know, it's slightly harder
> to implement, but...).
>
>               -s
>
> On Wed, Feb 9, 2011 at 04:34, Michel Talon <talon at lpthe.jussieu.fr
> <mailto:talon at lpthe.jussieu.fr>> wrote:
>
>     Hello,
>
>     i am trying to write a grind variant to convert expressions so
>     that they can
>     be embedded in Gnu GMP programs. In the course of doing that, i
>     have, of
>     course, consulted forta.lisp, grind.lisp and mactex.lisp, but i
>     see that
>     some expressions are of the following form:
>     niobe% maxima
>     (%i1) x:y*(z+t^2)$
>
>     (%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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