This is a wholly appropriate use of reduce; it's the obvious function to use when you want to "accumulate" some calculation over a sequence.
As you say, you can just produce a function that acts on the result, something like (defn fstep [c] (if (= c \<) pop #(conj % c)) However, the obvious way of accumulating the application of these functions is ... reduce: (reduce #(%2 %1) [] (map fstep input-chars)) You can gain some efficiency by using transient operations: (defn tstep [v c] (if (= c \<) (pop! v) (conj! v c))) ;cf. step (defn run [cs] (persistent! (reduce tstep (transient []) cs)) ; cf. run-program On my machine this reduced the runtime of your 6e6 test about 20% On Jul 24, 6:16 pm, samnardoni <samnard...@googlemail.com> wrote: > I have a simple string (or list of characters to be precise) in a form > of: "1234<5678<<9". > > I want to parse this string and end up with: "123569". > > The "<" is essentially the same as a "backspace". > > I managed to implement this fairly simply using the reduce function - > source:http://gist.github.com/489019. > > Although it can be implemented easily using the reduce function, I was > concerned with the performance (especially with large inputs). As the > reduce function invokes the provided function with the previous > result, this list that is getting built is being passed around a huge > amount. > > I'm not too sure as to what will be going on under the hood in this > sample. Whether the previous result of the function application is > really being passed around or not clear to me. > > For the program, I know that when processing a character, I do not > need the previous result. All I need is the current character, and I > can return a function that acts on the result. I'm not sure if this is > simple to implement in a functional way. > > So, I have 2 questions: > > 1) Is this a correct use of the reduce function? (I know there is a > clue in the word "reduce", but it's also called "inject" and else in > other languages.) > > 2) Is there a more efficient way of solving this? > > I appreciate any replies (for such a trivial topic). Answers to this > will hopefully enlighten me to using functional languages more > effectively, or possibly to a more suitable high-order function. -- 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
