On Sat, Jan 10, 2009 at 6:57 PM, CuppoJava <patrickli_2...@hotmail.com> wrote: > ps: I'm doing a bit of reading about mutually-recursive data > structures on the net. Is Lisp's letrec supposed to handle this > situation? > > It would be handy just to be able to do: > > (letrec [bob (create_person "bob" bill) > bill (create_person "bill" bob)])
If you want to draw inspiration from other languages, take a look at PLT Scheme's "shared" which is kind of like a letrec for creating mutually recursive data structures: http://docs.plt-scheme.org/reference/shared.html But in the absence of such a construct, you've got two main options. One is to use mutation to set up the mutual references, like what Stuart Sierra described. The other main option is to give each of your people a unique ID or name. You keep a hash table that maps these names to the actual person object. Within a person, your list of friends is actually a list of names, rather than a list of people objects. This adds a level of indirection that avoids mutual references and makes everything work. To get to the actual person object, you look up the name in your hash table. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
