Re: [Chicken-users] Re: I need some help to edit a tree

[Kon Lovett]

On Mar 1, 2007, at 9:09 AM, minh thu wrote:

> 2007/3/1, Kon Lovett <address@hidden>:
> > On Feb 28, 2007, at 2:28 PM, minh thu wrote:
<snip>
> Yes, that's what I do. But the problem is to descend in the tree to
> update the correct part. But I manage to it. The fact there's no
> lvalue is a bit disturbing : I need to write a procedure to get the
> value and another one the set it, both are similar but the setter
> needs to keep one more level to be able to use set-car!.

Well anything in Scheme that has the semantics of a storage cell is  
an "lvalue", so a cons cell, vector, string, etc. are lvalues. A  
character, fixnum, etc. are not lvalues.
(Immediates & Immutables are not lvalues.)

Yes, you need the cons cell to update an element. You have 2 kinds of  
elements, nodes & leaves. But if you only deal internally w/ nodes  
you always have a cons cell. The problem comes in w/ a leaf w/ a list  
value. If you never store a cons cell as leaf then ok, otherwise  
detecting a leaf-node is problematic. General purpose tree code  
usually uses a different representation of a node, a structure for  
example, for just this reason; some type disjoint from any type that  
is legal as a leaf value.

BTW, I think the SXML sxpath can navigate an arbitrary list.

> Do you think it's a good idea to write a kind of advanced
> libreadline/editor which operates on S-EXPs, not on strings ? To
> manage source code, documenting it, ...

Remember source code has textual comments that are not s-exps. Also,  
forms like '#;' & '#|...|#' are invisible to the reader but should be  
visible to a source editor.

Yes, a Scheme source editor in Scheme would be nice. An essential  
component of a "pure" Chicken IDE. However, it must deal w/ embedded  
C-family code, textual comments, etc. Not an easy proposition.

Best Wishes,
Kon

> Thanks,
> thu