Thanks again. I do get it. I'm not saying that apply has effects other than the result it returns. No, it's not a side-effect; it doesn't change something in the environment in passing. What it changes is the expected result, if you expect that, as Rich Hickey is supposed to have written, (apply f [i]) can be written (f i)
This effect is, on the face of it, unpredictable: you just have to know that that is what apply does. Users of clojure learn that pretty quickly. I've just learned it. Doc doesn't help. user=> (doc apply) > > ------------------------- > > clojure.core/apply > > ([f args] [f x args] [f x y args] [f x y z args] [f a b c d & args]) > > Applies fn f to the argument list formed by prepending intervening >> arguments to args. > > nil > > > If you are looking, for some reason I can't imagine at the moment, for a function that acts just like a funcall, so that (funcall f [i]) is exactly equivalent to (f [i]), I guess you are out of luck. I don't know how other lisps deal with "linearising" argument lists? I'd be interested to hear. On Sunday, 16 December 2012 10:21:36 UTC+10, puzzler wrote: > > On Sat, Dec 15, 2012 at 3:58 PM, Peter West <peter....@gmail.com<javascript:> > > wrote: > >> But it can't, can it? In this context (apply f [i]) with respect to (f i) >> * apply *has *side-effects*! >> > > This doesn't really make any sense. There are no side effects here. I > think maybe you just don't understand what apply does. Let me try to > explain it a different way. > > Some functions, like +, are designed to take 1, 2, 3, 4, 5, or any number > of arguments. You can write: > (+ 1 2) > (+ 1 2 3) > (+ 1 2 3 4) > (+ 1 2 3 4 5) > etc. > The "contract" for + is that it takes any number of numbers as an input. > > One thing + can't do is add up the numbers in a list, at least not when > written in this way: > (+ [1 2 3 4 5]) > This doesn't make any sense, because + is expecting numbers, and we passed > it a vector. > > It might seem somewhat ironic that + can't take a list of numbers. > Obviously, it knows how to add a series of numbers, it just expects them to > be one after each other, as arguments, not all bundled up in a list. > > If only we could delete those brackets around [1 2 3 4 5]... If only we > had some sort of "adapter" that could take a list/vector of items, and pass > them in as multiple arguments to a function that was designed to take > multiple arguments... > > That is what apply does. > > (apply + [1 2 3 4 5]) turns into > (+ 1 2 3 4 5) > > Similarly, > (apply str [\a \b \c \d]) turns into > (str \a \b \c \d) > > > -- 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
