Re: toUpperCase on java.lang.String
On Oct 16, 4:29 pm, Rich Hickey <[EMAIL PROTECTED]> wrote: > On Oct 15, 11:47 pm, "Stephen C. Gilardi" <[EMAIL PROTECTED]> wrote: > > > > > Hi Parth, > > > > But if I do this in a doto, it doesn't seem to work but > > > I don't get any error message. > > > > user=> (doto (new java.lang.String "hello") (toUpperCase)) > > > "hello" > > > user=> (class (new java.lang.String)) > > > #=java.lang.String > > > > Shouldn't this be working? If this is (by design) because strings are > > > immutable (so no doto) shouldn't there be an error message? > > > > What am I missing here. > > > "doto" operates on an object and returns the object that it operated > > on. In your case, it's the original string that gets returned. Strings > > are immutable so the toUpperCase call created a new string which was > > then thrown away. > > > The "->" operator will accomplish what you're looking for here. It > > returns the result of the operations, each result becoming the input > > for the next:: > > > user=> (-> (String. "hello") .toUpperCase) > > "HELLO" > > Another semantic marker here is 'do'. do in Clojure implies side- > effects. Since you can't uppercase a string by side effect, doto isn't > the right tool for this job. > > doto can't throw an error here or elsewhere when used on an immutable > object because: > > a) It can't generally know which objects are immutable > b) Even immutable objects may have methods with other side-effects > > Rich That makes sense. Thanks everyone for all the help. Parth --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: toUpperCase on java.lang.String
On Oct 16, 2008, at 7:29 AM, Rich Hickey wrote:
> Another semantic marker here is 'do'. do in Clojure implies side-
> effects. Since you can't uppercase a string by side effect, doto isn't
> the right tool for this job.
Neat.
I explored the "do..." marker a little with Clojure:
- user=> (filter #(re-matches #"do.*" %) (map #(-> % first name) (ns-
publics 'clojure)))
("dorun" "doseq" "dosync" "dotimes" "doubles" "doto" "double-array"
"doall" "double" "doc")
The "do implies a side-effect emphasis" pattern holds for dorun,
doseq, dosync, dotimes, doto, and doall.
- The doc for the function "repeatedly" mentions "presumably with
side effects", but it doesn't begin with "do".
- The special form "do" is just about grouping, independent of side
effects.
I recently changed the clojure.contrib.sql/with-results macro to
remove a "doseq" call. Now it just provides the sequence of results
and lets the caller decide what to do with it which is a lot more
flexible.
Coming from an imperative programming mindset, I find that imperative/
side-effecting is often the first thing that occurs to me. When I work
on the code to make it more functional, it's pretty much uniformly an
improvement in how flexible and composable it is.
As a very welcome bonus, I'm also finding it's a lot more fun!
--Steve
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Re: toUpperCase on java.lang.String
On Oct 15, 11:47 pm, "Stephen C. Gilardi" <[EMAIL PROTECTED]> wrote: > Hi Parth, > > > But if I do this in a doto, it doesn't seem to work but > > I don't get any error message. > > > user=> (doto (new java.lang.String "hello") (toUpperCase)) > > "hello" > > user=> (class (new java.lang.String)) > > #=java.lang.String > > > Shouldn't this be working? If this is (by design) because strings are > > immutable (so no doto) shouldn't there be an error message? > > > What am I missing here. > > "doto" operates on an object and returns the object that it operated > on. In your case, it's the original string that gets returned. Strings > are immutable so the toUpperCase call created a new string which was > then thrown away. > > The "->" operator will accomplish what you're looking for here. It > returns the result of the operations, each result becoming the input > for the next:: > > user=> (-> (String. "hello") .toUpperCase) > "HELLO" > Another semantic marker here is 'do'. do in Clojure implies side- effects. Since you can't uppercase a string by side effect, doto isn't the right tool for this job. doto can't throw an error here or elsewhere when used on an immutable object because: a) It can't generally know which objects are immutable b) Even immutable objects may have methods with other side-effects Rich --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: toUpperCase on java.lang.String
Thanks! --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: toUpperCase on java.lang.String
Hi, On 16 Okt., 08:17, Timothy Pratley <[EMAIL PROTECTED]> wrote: > What does 'mix in non-methods' means? I read the (doc ->) but I really > don't follow that explination. -> is more general than .. . .. only works on objects. (.. foo (bar baz) (frob nicate)) is equivalent to (. (. foo bar baz) frob nicate) However -> works on everything, but with the same idea. user=> (-> true (if inc dec) (map [1 2 3])) (2 3 4) or expanded (map (if true inc dec) [1 2 3]) So one can also use macros and normal functions in ->, ie. non-methods. Sincerely Meikel --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: toUpperCase on java.lang.String
Oh wow, powerful syntax! > user=> (-> "hello" .toUpperCase (.replace "H" "J")) > "JELLO" > .. would also work, but I pretty much always prefer -> because you can > mix in non-methods, and the methods are clearly indicated with a > leading dot. In fact, I could imagine lobbying to have .. removed > (while we're making breaking changes...) What does 'mix in non-methods' means? I read the (doc ->) but I really don't follow that explination. I agree that (-> is a much nicer syntax than (.. and now that I see how you use it will use it instead. Speaking of which... I have to say that for someone getting their head around form expressions the docs are quite terse. Its not always trivial to find a simple example (I usually find something searching the groups and wiki and non-api sections of the website). IMHO The docs would really benefit from an example for each entry. Now I know that is a great deal of work, so I've started a wiki entry: http://en.wikibooks.org/wiki/Clojure_Programming_Examples Where I'm attempting to gather examples I come across from various sources which have helped me. The idea being that if it ever gets close to covering the api, they could be somehow programatically stripped into the (doc and voila there would be examples for every syntax definition. Just meantioning so that others can look/add and or comment on the idea. Regards, Tim. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: toUpperCase on java.lang.String
Hi Parth, > But if I do this in a doto, it doesn't seem to work but > I don't get any error message. > > user=> (doto (new java.lang.String "hello") (toUpperCase)) > "hello" > user=> (class (new java.lang.String)) > #=java.lang.String > > Shouldn't this be working? If this is (by design) because strings are > immutable (so no doto) shouldn't there be an error message? > > What am I missing here. "doto" operates on an object and returns the object that it operated on. In your case, it's the original string that gets returned. Strings are immutable so the toUpperCase call created a new string which was then thrown away. The "->" operator will accomplish what you're looking for here. It returns the result of the operations, each result becoming the input for the next:: user=> (-> (String. "hello") .toUpperCase) "HELLO" --Steve --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: toUpperCase on java.lang.String
On Wed, Oct 15, 2008 at 11:20 PM, Parth Malwankar <[EMAIL PROTECTED]> wrote: > > But if I do this in a doto, it doesn't seem to work but > I don't get any error message. > > user=> (doto (new java.lang.String "hello") (toUpperCase)) > "hello" > user=> (class (new java.lang.String)) > #=java.lang.String doto returns the original object, not the results of any of the following method calls. That means it works well for mutable objects, where in the end you want the mutated object. But since Strings are immutable, methods like toUpperCase are returning a new String, not mutating the old one. So all you're getting back is your original String. Perhaps -> would work better in this case: user=> (-> "hello" .toUpperCase (.replace "H" "J")) "JELLO" .. would also work, but I pretty much always prefer -> because you can mix in non-methods, and the methods are clearly indicated with a leading dot. In fact, I could imagine lobbying to have .. removed (while we're making breaking changes...) --Chouser --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
toUpperCase on java.lang.String
Calling a java method on a string directly works. user=> (.toUpperCase "hello") "HELLO" user=> (class "hello") #=java.lang.String But if I do this in a doto, it doesn't seem to work but I don't get any error message. user=> (doto (new java.lang.String "hello") (toUpperCase)) "hello" user=> (class (new java.lang.String)) #=java.lang.String Shouldn't this be working? If this is (by design) because strings are immutable (so no doto) shouldn't there be an error message? What am I missing here. Parth --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
