Sorting gotcha
I had always assumed that vectors were sorted lexicographically. In other words, you sort on the first element, and then refine by the second element, and so on. I was surprised tonight to discover that is not the case. (compare abc b); Strings are compared lexicographically -1 (compare (vec abc) (vec b)); Vectors are not 1 It turns out that shorter vectors are always considered to be less than longer vectors. Lexicographic behavior only kicks in among vectors of the same length. Not at all what I expected, so I wanted to make sure everyone knew about this behavior. -- 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
Re: a question about using the delay macro
perfect answer. thank you ! btw: my snippet is taken out of the docs for java.jdbc. On Aug 22, 12:04 pm, Meikel Brandmeyer (kotarak) m...@kotka.de wrote: Hope, I'm not too far off. 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 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
Re: Sorting gotcha
On Tue, Aug 23, 2011 at 09:44, Mark Engelberg mark.engelb...@gmail.com wrote: I had always assumed that vectors were sorted lexicographically. In other words, you sort on the first element, and then refine by the second element, and so on. I was surprised tonight to discover that is not the case. (compare abc b) ; Strings are compared lexicographically -1 (compare (vec abc) (vec b)) ; Vectors are not 1 It turns out that shorter vectors are always considered to be less than longer vectors. Lexicographic behavior only kicks in among vectors of the same length. Not at all what I expected, so I wanted to make sure everyone knew about this behavior. Yea, confirmed. $ git describe clojure-1.3.0-beta1-6-g82c7254 $ java -jar target/clojure-1.3.0-master-SNAPSHOT.jar Clojure 1.3.0-master-SNAPSHOT user= (defn sort* [ more ] (sort more)) ;; strings: always sort lexicographically user= (sort* abc b) (abc b) ;; vector: short sorts before long user= (sort* (vec abc) (vec b)) ([\b] [\a \b \c]) ;; vector: same length sorts lexicographically user= (sort* (vec abc) (vec abb)) ([\a \b \b] [\a \b \c]) user= (sort* (vec abc) (vec abd)) ([\a \b \c] [\a \b \d]) ;; seq: does not implement comparable user= (sort* (seq abc) (seq b)) ClassCastException clojure.lang.StringSeq cannot be cast to java.lang.Comparable clojure.lang.Util.compare (Util.java:92) user= (sort* (seq (vec abc)) (seq (vec b))) ClassCastException clojure.lang.PersistentVector$ChunkedSeq cannot be cast to java.lang.Comparable clojure.lang.Util.compare (Util.java:92) ;; list: does not implement comparable user= (sort* (apply list abc) (apply list b)) ClassCastException clojure.lang.PersistentList cannot be cast to java.lang.Comparable clojure.lang.Util.compare (Util.java:92) It seems a shame that Clojure doesn't provide universal lexicographical comparability of sequential things, much as it provides equality for sequential things: user= (= (list \a \b \c) (vector \a \b \c)) true Perhaps there's a good reason for this (law of unintended consequences, anyone?) that I'm not seeing. // Ben -- 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
How to import libs in Clojure?
Hello, win XP, clojure 1.2.1 and clojure.contrib-1.2.0.jar here. i want to learn clojure (background python and javascript and a bit Haskell) and are currently reading the pdf 'Programming Clojure' from 2009. In Chapter 1.3: 'Exploring Clojure Libraries' it says: Clojure code is packaged in libraries. Each Clojure library belongs to a namespace, which is analogous to a Java package. You can load a Clojure library with require: (require quoted-namespace-symbol) When you require a library named clojure.contrib.str-utils, Clojure looks for a file named clojure/contrib/str-utils.clj on the CLASSPATH. Try it: user= (require 'clojure.contrib.str-utils) nil i did. i got: user= (require 'clojure.contrib.str-utils) java.io.FileNotFoundException: Could not locate clojure/contrib/ str_utils__init.class or clojure/contrib/str_utils.clj on classpath: (NO_SOURCE_FILE:0) i googled a bit. i now know that: * if you type str-utils it searches for str_utils.clj, not str- utils.clj btw. my pdf is wrong (or old) here. * setting CLASSPATH doesnt help (JAVA_HOME is set btw). * setting classpath directly with ... java -classpath C:\CLOJURE\lib\clojure-contrib-1.2.0.jar -cp clojure.jar clojure.main ... doesnt help. * doing add-classpath seemed to work for a guy @ http://stackoverflow.com/questions/1805081/clojure-cant-find-clj-in-local-directory-and-classes-on-classpath but a) not for me ... user= (add-classpath file:///C:/CLOJURE/lib/clojure- contrib-1.2.0.jar) WARNING: add-classpath is deprecated nil user= (println (seq (.getURLs (java.lang.ClassLoader/ getSystemClassLoader (#URL file:/C:/CLOJURE/bin/clojure.jar) nil ... and b) it is depreaced. both str_utils__init.class and clojure/contrib/str_utils.clj are contained in this contrib jar at the right position. I tried removing the numbers from the jar. i tried extracting the contents of the jar. i tried moving the contrib folder to C:\CLOJURE\bin\src\clj\clojure. li tried moving the contrib jar to C:\CLOJURE\bin. Now i need a hint. How to import libs in Clojure? greets, Wanderfels -- 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
Re: How to import libs in Clojure?
Hi On 23 August 2011 12:10, Wanderfels wanderf...@web.de wrote: Hello, win XP, clojure 1.2.1 and clojure.contrib-1.2.0.jar here. i want to learn clojure (background python and javascript and a bit Haskell) and are currently reading the pdf 'Programming Clojure' from 2009. In Chapter 1.3: 'Exploring Clojure Libraries' it says: Clojure code is packaged in libraries. Each Clojure library belongs to a namespace, which is analogous to a Java package. You can load a Clojure library with require: (require quoted-namespace-symbol) When you require a library named clojure.contrib.str-utils, Clojure looks for a file named clojure/contrib/str-utils.clj on the CLASSPATH. Try it: user= (require 'clojure.contrib.str-utils) nil i did. i got: user= (require 'clojure.contrib.str-utils) java.io.FileNotFoundException: Could not locate clojure/contrib/ str_utils__init.class or clojure/contrib/str_utils.clj on classpath: (NO_SOURCE_FILE:0) i googled a bit. i now know that: * if you type str-utils it searches for str_utils.clj, not str- utils.clj btw. my pdf is wrong (or old) here. * setting CLASSPATH doesnt help (JAVA_HOME is set btw). Depending on how you started the repl this may be ignored. * setting classpath directly with ... java -classpath C:\CLOJURE\lib\clojure-contrib-1.2.0.jar -cp clojure.jar clojure.main ... doesnt help. -cp is the short form of -classpath. If you want more than one thing on the classpath, you should use: java -classpath C:\CLOJURE\lib\clojure-contrib-1.2.0.jar;clojure.jar clojure.main (assuming you have clojure.jar in the current directory) or: java -cp C:\CLOJURE\lib\clojure-contrib-1.2.0.jar;clojure.jar clojure.main * doing add-classpath seemed to work for a guy @ http://stackoverflow.com/questions/1805081/clojure-cant-find-clj-in-local-directory-and-classes-on-classpath but a) not for me ... user= (add-classpath file:///C:/CLOJURE/lib/clojure- contrib-1.2.0.jar) WARNING: add-classpath is deprecated nil user= (println (seq (.getURLs (java.lang.ClassLoader/ getSystemClassLoader (#URL file:/C:/CLOJURE/bin/clojure.jar) nil ... and b) it is depreaced. It is indeed deprecated and may not work. Something to do with class loaders. Rather just specify the jar in the classpath manually on the command line, or better, use Leiningen as I'm sure others will tell you. both str_utils__init.class and clojure/contrib/str_utils.clj are contained in this contrib jar at the right position. I tried removing the numbers from the jar. i tried extracting the contents of the jar. i tried moving the contrib folder to C:\CLOJURE\bin\src\clj\clojure. li tried moving the contrib jar to C:\CLOJURE\bin. Now i need a hint. How to import libs in Clojure? greets, Wanderfels Basically you were on the right track, but the way you were specifying the classpath was wrong. Something like Leiningen or cake can help you with this sort of thing. They require you to create a project, which might seem strange coming from Python, but since they help with things like the classpath and downloading dependencies etc. that's generally worth the effort. e.g.: lein new myproject cd myproject edit project.clj (add the clojure.contrib.str-utils dependency) lein deps lein repl https://github.com/technomancy/leiningen#readme -- Michael Wood esiot...@gmail.com -- 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
Re: Video Slides on Pattern Matching and Predicate Dispatch in Clojure
In the ClojureScript case, you can do lazy compile time compilation instead, where the predicate call is really a macro that always expands into a predicate call but during compile time can check if the tree needs to be updated. This isn't as lazy as the runtime version but at least groups of extend-pred won't compile unnecessarily. The only other option I can see is to make the compile step like a hook that is integrated to the build process and runs at the very end. -Brent On Aug 22, 3:12 pm, David Nolen dnolen.li...@gmail.com wrote: On Mon, Aug 22, 2011 at 3:07 PM, Brent Millare brent.mill...@gmail.comwrote: For pattern matching code size is a one time cost. For predicate dispatch, that's a lot of code to generated, since every new predicate case will produce an entirely new tree. But perhaps people won't care that much. Only time and experience reports will tell. If you want, you can be lazy about compilation and only compile right before the call to the predicate only if a new predicate has been added since the last compilation. Also, we can be smart about how we do the cached tree check. After extend-pred is called, it wraps the current DAG tree with a compilation step. During the compilation step (made right before the call), the new DAG tree is made and replaces the old one. Note that there is no longer a check for new predicates. -Brent Interesting idea. One possible down side of lazy runtime compilation is that it makes it more difficult to target ClojureScript. David -- 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
Re: a question about using the delay macro
I was trying to construct a simple example of what I actually have in
my apps that use pooling on top of java.jdbc. My actual code *does*
work to create a singleton but you're right, I've contracted my code
too far in trying to create a simple example of it... I'll have
another attempt!
Sean
On Aug 22, 3:04 am, Meikel Brandmeyer (kotarak) m...@kotka.de
wrote:
Am Montag, 22. August 2011 11:53:32 UTC+2 schrieb faenvie:
yesterday i came across the following use of
the delay-macro:
(defn pooled-data-source
[db-connection-settings]
; this Fn creates and returns object of type PooledDataSource
)
(defn pooled-data-source-as-singleton
[db-connection-settings]
(let [datasource (delay (pooled-data-source db-connection-
settings))]
@datasource))
i am not sure, what the exact semantic of this is and if
it's safe in a multithreaded context.
What is the difference to using def/defonce ?
Someone who can explain ?
This snippet does not work as the original author intended. You can remove
the whole delay incantations and everything will work as before. That's
because each call of pooled-data-source-as-singleton creates a new delay,
forces it and throws it away immediately. What probably was intended, is the
use of memoize:
(def ^{:arglists ([db-connection-settings])} pooled-data-source-as-singleton
(memoize pooled-data-source))
The intention is to delay the creation of the datapool instance until
runtime and not do it on load time. This is also nice if you have your db
connection configurable in some non-code form. If you have only one db
connection, which is hardwired in some Var at load time, you can go with the
following:
(let [db-connection-pool (delay (pooled-data-source
db-connection-settings))]
(defn pooled-data-source-as-singleton
[]
@db-connection-pool))
This is maybe, what the original author had in mind.
Hope, I'm not too far off.
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Cron algorithm challenge
Hi! I have some challenge for you, sine it is easy express it in imperative language I would like to ask you if is it possible to create DSL to express such algorithm in clojure or if is it too complicated just write it in functional manner. The challenge is to write cron algorithm. I can express it in such way: http://pastebin.com/1ssvbJ8z Anyone? Thanks in advance! -- 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
Re: Cron algorithm challenge
After the post I suddenly saw the code in my mind: http://pastebin.com/kYYYirdb The expression abilities are truly near the mind. Clojure rox :-) On Aug 23, 6:01 pm, Michael Jaaka michael.ja...@googlemail.com wrote: Hi! I have some challenge for you, sine it is easy express it in imperative language I would like to ask you if is it possible to create DSL to express such algorithm in clojure or if is it too complicated just write it in functional manner. The challenge is to write cron algorithm. I can express it in such way:http://pastebin.com/1ssvbJ8z Anyone? Thanks in advance! -- 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
Re: Cron algorithm challenge
Hi,
Am 23.08.2011 um 18:01 schrieb Michael Jaaka:
I have some challenge for you, sine it is easy express it in
imperative language I would like to ask you if is it possible to
create DSL to express such algorithm in clojure or if is it too
complicated just write it in functional manner. The challenge is to
write cron algorithm. I can express it in such way:
http://pastebin.com/1ssvbJ8z
Here my try. Basic idea: Provide a sequence of times where things have to run
based on a pattern. A pattern is a vector of months, weekdays, days, hours and
minutes. Each may be a _ (read: don't care), a number or a set of numbers to
specify several allowed times. (One might also want to allow maps for ranges?)
The main function then waits till the next scheduled point in time. Executes
the function. Wait till the next scheduled point in time. …
Much is left to be desired: What if the next moment has already expired when f
completes? What does wait-till look like? Maybe cron-seq could be more clever
than brute force?
But I think you get the idea.
Sincerely
Meikel
(import 'org.joda.time.DateTime)
(defn cron-seq
[pattern]
(let [fix-up-pattern (fn [x]
(cond
(= x '_) nil
(set? x) x
:else#{x}))
[months weekdays days hours minutes]
(map fix-up-pattern pattern)]
(for [point-in-time (iterate #(.plusMinutes % 1) (DateTime/now))
:when (or (not minutes) (minutes (.getMinuteOfHour point-in-time)))
:when (or (not hours)(hours(.getHourOfDay point-in-time)))
:when (or (not days) (days (.getDayOfMonth point-in-time)))
:when (or (not weekdays) (weekdays (.getDayOfWeek point-in-time)))
:when (or (not months) (months (.getMonthOfYear point-in-time)))]
point-in-time)))
; Left as excercise.
(defn wait-till
[future-point-in-time]
(magic happens here))
(defn cron*
[pattern f args]
(loop [schedule-time (seq (cron-seq pattern))]
(when schedule-time
(wait-till (first schedule-time))
(apply f args)
(recur (next schedule-time)
(defmacro cron
[pattern command]
`(cron* ~(vec (map #(if (= % '_) `(quote ~%) %) pattern)) ~@command))
; Usage:
(cron [#{1 4 7 10} _ _ 6 30] do-something with arguments)
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Odp: Re: Cron algorithm challenge
Wow nice! :-)
Of course wait-till can be done with Timers build-in JDK.
And here is a proposition for cron parsing function:
(defn parse-cron-expr[ pattern ]
(let[ cal (Calendar/getInstance) ]
(let [[min-pat hour-pat day-pat month-pat week-pat] (letfn[ (parse-cron[ val
pos cal ]
(letfn[ (range-values[ val ]
(if-let[ [ gr min max ] (first (re-seq #([\d]+)-([\d]+) val)) ]
(range (Integer. min) (inc (Integer. max)))
(if (= val *)
(condp = pos Calendar/DAY_OF_WEEK nil Calendar/DAY_OF_MONTH nil
(map (if (= pos Calendar/MONTH) inc identity)
(range (.getMinimum cal pos) (inc (.getMaximum cal pos)
[(Integer. val)]) )) ]
(let[ [ tx re div ] (first (re-seq #([^\/]+)/?([\d]+)? val))
div-n (or (nil? div) (Integer. div)) ]
(filter #(or (nil? div) (= (mod %1 div-n) 0))
(sort (distinct (mapcat range-values (re-seq #[^\,]+ re
(into-set[ cal val ]
(into #{} val))
(into-weeks[ cal val ]
(let [ z (zipmap (range 1 8) (iterate #(inc (mod %1 7)) (.getFirstDayOfWeek
cal))) ]
(into-set cal (map #(get z %1) val
(into-months[ cal val ]
(into-set cal (map dec val))) ]
(let[ cal (repeat cal) ]
(map #(%1 %2 %3) [into-set into-set into-set into-months into-weeks]
cal (map parse-cron (re-seq #[\S]+ pattern)
[ Calendar/MINUTE Calendar/HOUR_OF_DAY Calendar/DAY_OF_MONTH
Calendar/MONTH Calendar/DAY_OF_WEEK ] cal) ))) ]
(if (and (empty? day-pat) (empty? week-pat))
[min-pat hour-pat day-pat month-pat
(into #{} (range (.getMinimum cal Calendar/DAY_OF_WEEK) (inc (.getMaximum
cal Calendar/DAY_OF_WEEK ]
[min-pat hour-pat day-pat month-pat week-pat]
and use is
(parse-cron-expr 0 10 10-13 * 1-5)
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Re: How to import libs in Clojure?
Did you use the -cp option to include the contrib when running java.exe on clojure.jar? The error shows that it's looking in a subdirectory with a .class rather than the packaged jar file. I'd suggest using leiningen to avoid build problems like this. On Aug 23, 6:10 am, Wanderfels wanderf...@web.de wrote: Hello, win XP, clojure 1.2.1 and clojure.contrib-1.2.0.jar here. i want to learn clojure (background python and javascript and a bit Haskell) and are currently reading the pdf 'Programming Clojure' from 2009. In Chapter 1.3: 'Exploring Clojure Libraries' it says: Clojure code is packaged in libraries. Each Clojure library belongs to a namespace, which is analogous to a Java package. You can load a Clojure library with require: (require quoted-namespace-symbol) When you require a library named clojure.contrib.str-utils, Clojure looks for a file named clojure/contrib/str-utils.clj on the CLASSPATH. Try it: user= (require 'clojure.contrib.str-utils) nil i did. i got: user= (require 'clojure.contrib.str-utils) java.io.FileNotFoundException: Could not locate clojure/contrib/ str_utils__init.class or clojure/contrib/str_utils.clj on classpath: (NO_SOURCE_FILE:0) i googled a bit. i now know that: * if you type str-utils it searches for str_utils.clj, not str- utils.clj btw. my pdf is wrong (or old) here. * setting CLASSPATH doesnt help (JAVA_HOME is set btw). * setting classpath directly with ... java -classpath C:\CLOJURE\lib\clojure-contrib-1.2.0.jar -cp clojure.jar clojure.main ... doesnt help. * doing add-classpath seemed to work for a guy @http://stackoverflow.com/questions/1805081/clojure-cant-find-clj-in-l... but a) not for me ... user= (add-classpath file:///C:/CLOJURE/lib/clojure- contrib-1.2.0.jar) WARNING: add-classpath is deprecated nil user= (println (seq (.getURLs (java.lang.ClassLoader/ getSystemClassLoader (#URL file:/C:/CLOJURE/bin/clojure.jar) nil ... and b) it is depreaced. both str_utils__init.class and clojure/contrib/str_utils.clj are contained in this contrib jar at the right position. I tried removing the numbers from the jar. i tried extracting the contents of the jar. i tried moving the contrib folder to C:\CLOJURE\bin\src\clj\clojure. li tried moving the contrib jar to C:\CLOJURE\bin. Now i need a hint. How to import libs in Clojure? greets, Wanderfels -- 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
why is it necessary to use identity to check for nils in an if statement
this doesn't work: user= (defn if-a [a b] (if (a) (str a) (str b))) #'user/if-a user= (if-a nil b) java.lang.NullPointerException (NO_SOURCE_FILE:0) user= (if-a a nil) user= java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0) this does work: user= (defn if-a [a b] (if (identity a) (str a) (str b))) #'user/if-a user= (if-a nil b) b user= (if-a a nil) a why is the identity function is needed? 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 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
Re: why is it necessary to use identity to check for nils in an if statement
You have an extra set of parens around a, treating it as a function call. Try: (defn if-a [a b] (if a (str a) (str b))) Hope that helps, Dave On Tue, Aug 23, 2011 at 4:37 PM, Andrew Xue and...@lumoslabs.com wrote: this doesn't work: user= (defn if-a [a b] (if (a) (str a) (str b))) #'user/if-a user= (if-a nil b) java.lang.NullPointerException (NO_SOURCE_FILE:0) user= (if-a a nil) user= java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0) this does work: user= (defn if-a [a b] (if (identity a) (str a) (str b))) #'user/if-a user= (if-a nil b) b user= (if-a a nil) a why is the identity function is needed? 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 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 -- 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
Re: why is it necessary to use identity to check for nils in an if statement
user= (defn if-a [a b] (if (a) (str a) (str b))) The problem is (a) - it tries to call a as a function, which throws NullPointer if a is nil. You meant: user= (defn if-a [a b] (if a (str a) (str b))) mg On Tue, Aug 23, 2011 at 9:37 PM, Andrew Xue and...@lumoslabs.com wrote: this doesn't work: user= (defn if-a [a b] (if (a) (str a) (str b))) #'user/if-a user= (if-a nil b) java.lang.NullPointerException (NO_SOURCE_FILE:0) user= (if-a a nil) user= java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0) this does work: user= (defn if-a [a b] (if (identity a) (str a) (str b))) #'user/if-a user= (if-a nil b) b user= (if-a a nil) a why is the identity function is needed? 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 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 -- 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
Creating a Clojure Record from a string
Given:
test=(defrecord Foo [A B])
test=(class (Foo. 1 2))
test.Foo
How do I:
test=(new test.Foo 1 2)
#:test.Foo{:A 1, :B 2}
Currently I get Unable to resolve classname: test/Foo.
Thanks,
Timothy
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Re: Creating a Clojure Record from a string
Given:
test=(defrecord Foo [A B])
test=(class (Foo. 1 2))
test.Foo
How do I:
test=(new test.Foo 1 2)
#:test.Foo{:A 1, :B 2}
Currently I get Unable to resolve classname: test/Foo.
Thanks,
Timothy
(Class/forName java.lang.String)
Be mindful of the performance...
Stu
Stuart Halloway
Clojure/core
http://clojure.com
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Re: Creating a Clojure Record from a string
Given:
test=(defrecord Foo [A B])
test=(class (Foo. 1 2))
test.Foo
How do I:
test=(new test.Foo 1 2)
#:test.Foo{:A 1, :B 2}
Currently I get Unable to resolve classname: test/Foo.
Check out
http://stackoverflow.com/questions/3748559/clojure-creating-new-instance-from-string-class-name.
Be sure to scroll down to see all the replies, since the macro one is
(IMO) the easiest to understand, although it has limitations.
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Re: Creating a Clojure Record from a string
(Class/forName java.lang.String) Oh, does that work in 1.3? Because (new (Class/forName user.Foo)) was the first thing I tried (under 1.2) and it doesn't work. Perhaps unsurprisingly given that new is a special form. -- 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
Re: Creating a Clojure Record from a string
On Aug 23, 3:39 pm, Craig Andera cand...@wangdera.com wrote: (Class/forName java.lang.String) Oh, does that work in 1.3? Because (new (Class/forName user.Foo)) was the first thing I tried (under 1.2) and it doesn't work. Perhaps unsurprisingly given that new is a special form. No. But you can use reflection to futz around with the class object, find its constructor, and then invoke that. -- 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
clojure.java.jdbc: mapping BigDecimal to double
Hi, It looks like Oracle NUMBER types get mapped to BigDecimal in a result seq from clojure.java.jdbc. Is there an easy way to configure clojure.java.jdbc/ResultSet to map Oracle NUMBERS to doubles? The resultset-seq from https://github.com/clojure/java.jdbc/blob/master/src/main/clojure/clojure/java/jdbc/internal.clj is below. (defn resultset-seq* Creates and returns a lazy sequence of structmaps corresponding to the rows in the java.sql.ResultSet rs. Based on clojure.core/ resultset-seq but it respects the current naming strategy. [^ResultSet rs] (let [rsmeta (.getMetaData rs) idxs (range 1 (inc (.getColumnCount rsmeta))) keys (map (comp keyword *as-key*) (map (fn [^Integer i] (.getColumnLabel rsmeta i)) idxs)) check-keys (or (apply distinct? keys) (throw (Exception. ResultSet must have unique column labels))) row-struct (apply create-struct keys) row-values (fn [] (map (fn [^Integer i] (.getObject rs i)) idxs)) rows (fn thisfn [] (when (.next rs) (cons (apply struct row-struct (row-values)) (lazy- seq (thisfn)] (rows))) -- 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
Re: Creating a Clojure Record from a string
test= (def foo-class-symbol (load-string test.Foo))
test= (def foo (eval (list 'new foo-class-symbol 1 2)))
test= foo
#:test.Foo{:A 1, :B 2}
Is that what you want?
On Aug 23, 6:24 pm, Timothy Baldridge tbaldri...@gmail.com wrote:
Given:
test=(defrecord Foo [A B])
test=(class (Foo. 1 2))
test.Foo
How do I:
test=(new test.Foo 1 2)
#:test.Foo{:A 1, :B 2}
Currently I get Unable to resolve classname: test/Foo.
Thanks,
Timothy
--
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that–lacking zero–they had no way to indicate successful termination
of their C programs.”
(Robert Firth)
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Re: clojure.java.jdbc: mapping BigDecimal to double
No, you'd have to do it yourself. Since not all BigDecimal values would fit correctly in double, it would be dangerous for resultset-seq to do it. I expect there are all sorts of JDBC data types that don't quite match Clojure types but I don't think automatically mapping them would be a good idea... Sean On Tue, Aug 23, 2011 at 6:16 PM, HiHeelHottie hiheelhot...@gmail.com wrote: It looks like Oracle NUMBER types get mapped to BigDecimal in a result seq from clojure.java.jdbc. Is there an easy way to configure clojure.java.jdbc/ResultSet to map Oracle NUMBERS to doubles? -- 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
Re: clojure.java.jdbc: mapping BigDecimal to double
Hey Sean, I really appreciate the quick response and your work with java.jdbc. Completely agree with you that it shouldn't automatically map out of the box. As a newbie to clojure and jdbc, do you have any advice on how I can get into resultset-seq* to do the mapping? I think it would be better not to have to map a BigDecimal to double after resultset- seq* returns a row. Are there any future plans to add a mapping api to resultset-seq or is the pattern just to chain any custom mappings after resultset-seq? On Aug 23, 9:41 pm, Sean Corfield seancorfi...@gmail.com wrote: No, you'd have to do it yourself. Since not all BigDecimal values would fit correctly in double, it would be dangerous for resultset-seq to do it. I expect there are all sorts of JDBC data types that don't quite match Clojure types but I don't think automatically mapping them would be a good idea... Sean On Tue, Aug 23, 2011 at 6:16 PM, HiHeelHottie hiheelhot...@gmail.com wrote: It looks like Oracle NUMBER types get mapped to BigDecimal in a result seq from clojure.java.jdbc. Is there an easy way to configure clojure.java.jdbc/ResultSet to map Oracle NUMBERS to doubles? -- 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
Re: clojure.java.jdbc: mapping BigDecimal to double
On Tue, Aug 23, 2011 at 9:54 PM, HiHeelHottie hiheelhot...@gmail.com wrote: Are there any future plans to add a mapping api to resultset-seq or is the pattern just to chain any custom mappings after resultset-seq? Is wrapping in (map double ...) too much typing? :) -- Protege: What is this seething mass of parentheses?! Master: Your father's Lisp REPL. This is the language of a true hacker. Not as clumsy or random as C++; a language for a more civilized age. -- 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
Re: clojure.java.jdbc: mapping BigDecimal to double
On Tue, Aug 23, 2011 at 6:54 PM, HiHeelHottie hiheelhot...@gmail.com wrote:
Completely agree with you that it shouldn't automatically map out of
the box. As a newbie to clojure and jdbc, do you have any advice on
how I can get into resultset-seq* to do the mapping? I think it would
be better not to have to map a BigDecimal to double after resultset-
seq* returns a row.
Apply something like this to the result?
(map (fn [row] (into {} (map (fn [[k v]] [k (some-mapping v)]) row))) results)
Are there any future plans to add a mapping api to resultset-seq or is
the pattern just to chain any custom mappings after resultset-seq?
Currently no plans. I don't want to add the overhead of map-over-map
for all users when I suspect only a few would want / need such a
mapping.
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Re: clojure.java.jdbc: mapping BigDecimal to double
the oracle jdbc adapter returns a whole host of strange datatypes. for instance, it returns bigdecimals for numbers you have mapped to be numbers (with a precision, without a scale) in the table. it also returns its own custom time classes. these generally have a toJdbc() method to convert them to the 'expected' jdbc type. a quick look under the covers of any other language's db libraries (such as activerecord or sequel) shows a whole host of these annoying conversions back and forth. to be honest, the lack of the conversion in java.jdbc is great as i can decide what i want to convert / not convert. tldr oracle jdbc is shit :P On Tue, Aug 23, 2011 at 8:54 PM, HiHeelHottie hiheelhot...@gmail.com wrote: Hey Sean, I really appreciate the quick response and your work with java.jdbc. Completely agree with you that it shouldn't automatically map out of the box. As a newbie to clojure and jdbc, do you have any advice on how I can get into resultset-seq* to do the mapping? I think it would be better not to have to map a BigDecimal to double after resultset- seq* returns a row. Are there any future plans to add a mapping api to resultset-seq or is the pattern just to chain any custom mappings after resultset-seq? On Aug 23, 9:41 pm, Sean Corfield seancorfi...@gmail.com wrote: No, you'd have to do it yourself. Since not all BigDecimal values would fit correctly in double, it would be dangerous for resultset-seq to do it. I expect there are all sorts of JDBC data types that don't quite match Clojure types but I don't think automatically mapping them would be a good idea... Sean On Tue, Aug 23, 2011 at 6:16 PM, HiHeelHottie hiheelhot...@gmail.com wrote: It looks like Oracle NUMBER types get mapped to BigDecimal in a result seq from clojure.java.jdbc. Is there an easy way to configure clojure.java.jdbc/ResultSet to map Oracle NUMBERS to doubles? -- 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 -- 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
