On Mon, Nov 9, 2009 at 10:54 PM, Waldek Hebisch wrote: > > Bill Page wrote: >> >> As you see above, there is not explicit pointer to an algebra object. >> >> Rep := Record(value: S) >> >> is simply a "container" for things of type S. >> >> ref v == [v] >> >> returns this container as an object. >> >> > Unfortunately there is also the stupid coercion to single interger >> > (hash) which is trivial. But one possibly could be to simply set the >> > hash of any object to the pointer referencing it. >> >> Of course with the definition above this is not possible. *If* FriCAS >> did provide a good hash value for things of type Record (it currently >> does not), then what you suggest would be possible. In that case one >> would return the hash for the container. >> > > Actually, reasonable hash for Record is unreasonable for references: > for Records use equality of components, for Reference we have: > > p = q == EQ(p, q)$Lisp > > which is quite different.
Yes you are right. I was wrong.(again) The hash function for Record does not make sense here. (Although a hash function for Record does make sense for it's own sake independent of this.) > Actually, looking at the above I think that if we want to use > Reference as pointers we really want: > > p = q == EQ(p.value, q.value)$Lisp > > which still is different than Record equality (which would uses > equality of values, Values of type Reference are not necessarily pointers but they are like memory addresses or variables that are not automatically de-referenced. This is just like &x in the C language. A pointer would be a "reference to a reference", i.e. something like this: q:=ref(3)$Reference(Integer) p:=ref(q)$Reference(Reference Integer) > why we want identity (Lisp EQ) here. > If p and q were pointers (references to references) you would be comparing their dereferenced values by EQ. Regards, Bill Page. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "FriCAS - computer algebra system" group. To post to this group, send email to fricas-devel@googlegroups.com To unsubscribe from this group, send email to fricas-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/fricas-devel?hl=en -~----------~----~----~----~------~----~------~--~---
