To add one small addendum to Mark's excellent comment, if you use lazy- seq then you don't need to worry about the nil from when
On Jul 24, 12:01 pm, Mark Engelberg <mark.engelb...@gmail.com> wrote: > On Sat, Jul 24, 2010 at 11:45 AM, Mark Engelberg > > <mark.engelb...@gmail.com> wrote: > > The simplest translation is to wrap a lazy-seq around the last line to > > avoid the stack overflows. > > Just to clarify, there are at least three reasonable places to place > the call to lazy-seq. You can put lazy-seq around the full body of > the function. You can place it around the cons. You can place it > around the recursive call to scheme-remove-first. Each choice results > in slightly different laziness behavior, i.e., when various elements > are computed, but the overall semantics of the sequence remains the > same and stack overflows will be avoided. Placing the lazy-seq around > the recursive function call will cause scheme-remove-first to compute > the first element right away, and delay the rest. Placing the > lazy-seq around the full body will prevent any computation until it is > asked for by a consumer. Placing the lazy-seq around the cons results > in in immediate behavior for the nil and > removable-item-at-front-of-list case, and delayed behavior otherwise. > All are acceptable choices, but preferences vary. Probably placing > lazy-seq around the full body is the most common style you'll see in > Clojure, although I tend to place it where the laziness is actually > required (like around the recursive call, or around the cons). > > You've probably noticed from the other samples posted that many > Clojurians prefer to use (seq lst) instead of (not (empty? lst)), and > organize their code around the not-empty case. > > So (if (empty? lst) empty-case not-empty-case) becomes (if (seq lst) > not-empty-case empty-case) > > When the empty case also results in nil, you can replace the if > structure with a one-armed when, because when automatically returns > nil in the other case. > > So (if (seq lst) not-empty-case nil) becomes (when (seq lst) not-empty-case). -- 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
