|printing recursive objects? email@example.com (Paul Haahr) (1993-05-03)|
|Re: printing recursive objects? firstname.lastname@example.org (John Lacey) (1993-05-04)|
|printing recursive objects? email@example.com (Tony Kanawati) (1993-05-04)|
|printing recursive objects? firstname.lastname@example.org (1993-05-05)|
|From:||Tony Kanawati <email@example.com>|
|X-Organization:||Ontos, Inc.; Burlington, Mass; USA|
|Date:||Tue, 4 May 1993 16:23:30 GMT|
|X-Phone:||(617) 272-7110 x328|
> Given an arbitrary recursive structure, say a lisp sexpr, how do you print
> it in a form that can be read back to create the same structure?
With pure data and a Lisp/Scheme READ/WRITE procedures, it is not possible
to perform your task; because you cannot print nor read *REFERENCES*.
However, if you really need to do this, you can create procedures that
read and write such structures using the following concepts:
1. Traverse the recursive circular structure, as a graph, and associate
each object with a unique number. This can be done using the eq?
predicate for identity testing, which will also make sure that you do
not loop forever.
*. Now, you should have a list of all the unique objects in your structure.
2. Each object should be one of:
a. Atom, or
b. cons ref1 ref2
c. vector of size N, contents: ref1 ... refN
With a multi-pass read/write policy, you will be able to construct the
objects, and then link them together, and recreate the original
Algorithms that come to mind: Graph traversal (depth first, breadth
first), topological sorting (may simplify the construction sequence).
Antoun (Tony) Kanawati | ONTOS, Inc., 3 Burlington Woods
firstname.lastname@example.org | Burlington, MA 01803, USA
uunet!uupsi!ontos!tonyk | (617) 272-8101 (Fax)
(800) 388-7110 x328 (Direct) | (617) 272-7110 x328 (Front desk)
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