I've been trying to implement stacks using vectors in Clojure. In case you wonder why, it's because I need stacks with a fast item count operation. While experimenting I discovered some vector properties which were unexpected.
conj adds at the end of the vector as expected: user> (conj [1 2 3] 4) [1 2 3 4] However, after reading "Programming Clojure" (page 114) I expected to be able to use sequence functions, such as drop-last, without my vectors changing representation. It seems this is not the case, as after calling drop-last (or indeed any of the seq functions) conj no longer adds at the end: user> (conj (drop-last 1 [1 2 3]) 4) (4 1 2) I don't know if it also has performance implications (does it turn my vector into a list?). So it turns out that pretty much the only operations I can use on my vectors are subvec and pop: user> (conj (subvec [1 2 3] 0 2) 4) [1 2 4] user> (conj (pop [1 2 3]) 4) [1 2 4] user> I didn't expect this to happen. Most tutorials (and Stuart Halloway's book) emphasize the generality of the sequence functions, only mentioning that subvec is faster for vectors. I think the fact that they also change subsequent behavior of conj is fundamental and should be printed in bold type. Am I missing something here? And while we're on the subject -- any hints for implementing a stack with a fast item count? (apart from a list with a separate counter) --J. --~--~---------~--~----~------------~-------~--~----~ 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 Note that posts from new members are moderated - please be patient with your first post. 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 -~----------~----~----~----~------~----~------~--~---
