I don't think I have any misconceptions. I probably haven't expressed myself clearly. Clojure has many very useful functions that return lazy sequences. Analogous functions in other languages perform what are exactly the same operations, but for the fact that what's returned is not a lazy sequence, but instead is a different kind of sequential structure. For example, Common Lisp's mapcar is very much like Clojure's map, but mapcar returns a (non-lazy) singly-linked list. As you point out, there are also functions in Clojure that return sequential structures that are not lazy. Moreover, it's easy to convert a lazy sequence into a non-lazy sequence through use of, for example, doall or vec.
However, writing code in Clojure that *only* used non-lazy sequences would unnatural and verbose. No one would bother doing that. Part of what's great about Clojure is the convenience of its collection of sequence operations. If you're not using those, you're not getting full benefit from Clojure. So as a practical matter, you must deal with laziness in Clojure. However, almost the same language could be constructed without any laziness, just be replacing lazy functions such as map with non-lazy analogues. In that case, you could do all of the same things, in those situations that don't require laziness. (You couldn't use lazy sequences, and you'd have to worry about keeping large data structures in memory, etc. But in many situations, those features aren't needed.) That's what I mean by "turning off laziness": Replacing every function that returns a lazy sequence with its closest non-lazy analogue. On Saturday, October 11, 2014 12:01:34 PM UTC-5, Jan-Paul Bultmann wrote: > > I feel that there are some misconceptions here, > Clojure is not a language that has lazy evaluation, > but is instead completely eager. > Macros are the closest thing that come to laziness, but they are still > different. > However, Clojure has a data structure, that also serves as an abstraction > layer, > that implements laziness, called a sequence or seq. > > Therefor “turning of laziness” makes no real sense. You could say “disable > the laziness of seqs”, > but that doesn’t really make sense either. It’s like disabling the FIFO > nature of a queue or a channel. > If you don’t want the properties of a seq, then use another data > structure, like a vector. > > > On 11 Oct 2014, at 18:14, Mars0i <mars...@logical.net <javascript:>> > wrote: > > Thanks Jan-Paul. That's helpful. I wonder whether, if all lazy functions > were rewritten in terms of transducers, it would then be easy to turn > laziness on and off. (I am not suggesting that this should be done. No > doubt it would entail a lot of work, and performance tradeoffs. I'm quite > happy with Clojure as it is, despite anything negative I might say about > impacts of laziness in some circumstances.) > > On Saturday, October 11, 2014 5:00:36 AM UTC-5, Jan-Paul Bultmann wrote: >> >> Transducers build up transformation steps, with new generic operations >> like single arg `map` and `filter`, and then apply these transformations >> to a collection using an evaluation function. >> This function decides if operations are done lazily, eagerly, or on a >> channel. >> >> Note that while this makes the place where laziness occurs more obvious, >> it is not really new. >> You can currently infer as well that `map` `filter` `concat` e.t.c are >> lazy. While `mapv` or `filterv` are not. >> >> >> On 11 Oct 2014, at 00:28, Mars0i <mars...@logical.net> wrote: >> >> >> >> On Friday, October 10, 2014 5:20:30 PM UTC-5, Mars0i wrote: >>> >>> Maybe an ideal world would be one in which there was a global setting >>> to turn laziness on and off. When you want it, have it, and know your >>> risks. After looking at the source for some of the lazy functions, I've >>> come to suspect that such a feature would be completely nontrivial. >>> >> >> Oh, wait, Rich Hickey's blog post about transducers >> <http://blog.cognitect.com/blog/2014/8/6/transducers-are-coming> says: >> >> >> >> >> >> *But transducers can also be used for: a la carte laziness ... >> collection/iteration/laziness-free transforming reductions * >> >> Not certain what this means. Haven't fully grokked reducers. >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clo...@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+u...@googlegroups.com >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+u...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> >> >> > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clo...@googlegroups.com <javascript:> > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+u...@googlegroups.com <javascript:> > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+u...@googlegroups.com <javascript:>. > For more options, visit https://groups.google.com/d/optout. > > > -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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