On Mar 2, 3:29 am, Mark Volkmann <r.mark.volkm...@gmail.com> wrote: > On Sun, Mar 1, 2009 at 11:06 PM, max3000 <maxime.lar...@gmail.com> wrote: > > > Hi, > > > I find the laziness in clojure very hard to wrap my head around. I > > understand the idea and it's probably nice in theory. However, in real > > life it doesn't seem really useful beyond hardcore mathematical > > problems. > > I felt the same way at first. I think it would help if the group > shared some common, non-mathematical cases, where laziness is helpful. > > I'll share this one which is described near the end of the section on > "Input/Output" athttp://www.ociweb.com/mark/clojure/article.html#IO. > > The line-seq function takes a java.io.BufferedReader and returns a > lazy sequence of all the lines of text in it. The significance of > returning a lazy sequence is that it doesn't really read all of the > lines when it is called. That could consume too much memory. Instead > it reads a line each time one is requested from the lazy sequence. > > Another way to think about this is that it allows writing functions > that return all the data a caller might want without having to know > ahead of time how much each caller might want. It may be the case that > a caller just wants the first piece of data or three pieces or all of > them. As the writer of the function that returns the data, you don't > have to care about that. > > -- > R. Mark Volkmann > Object Computing, Inc.
I also struggled (still struggle) with laziness. My main objection was that lazy/non-lazy sequences is not a hidden abstraction - ie you really need to know if what you are asking for is actually being produced. I am slowly changing my mind. I now consider every seq operation to be lazy, which means I only need to think about the cases where I map for side effects. I really like the above suggestion that the compiler warn about lazy computation that is thrown away. Another very subtle (at least I think so) point about lazyness is that you need to be VERY careful about using refs in a lazy seq. Because the work for creating a seq is deferred, the dereference will happen later than what you possibly expect. I'd also like to see a warning in the compiler that says "Don't use refs inside lazy seqs" Cheers, Brad --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
