Re: clojure.contrib.logging in side-effect free functions?
Hi! On Jun 24, 12:04 pm, ka sancha...@gmail.com wrote: To my naive inexperienced eyes, there doesn't seem to be something obviously wrong with your code. Since FOR returns a lazy sequence of the results, is this function safe? (Seeing that it is not side-effect free?) I'm not getting this, do you foresee any safety issues? I think that the logs will be created as you're writing to the out.csv. If you want the logs be written before you start writing to out.csv, you may realize the lazy-seq for returns. I am creating log entries as I read the lines. My worry was that I might get the log writer being interrupted in the middle of a line write. This I figure will be easily handled by the agent in the logger package. (I have perused the logging code and found that the agent is used to serialize write requests. So the code will work fine.) BTW: clojure.contrib.loggingindicates that it can use an agent for logging. Is my assumption that invoking the logger (with or without an agent) within a function would still mean that the function has side-effects correct? Yes, any change in state or IO means side effect. - Thanks Thanks. Martin. -- 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.contrib.logging in side-effect free functions?
Hi!
On Jun 24, 12:16 pm, Laurent PETIT laurent.pe...@gmail.com wrote:
2010/6/24 Laurent PETIT laurent.pe...@gmail.com:
Hi,
2010/6/17 William Wadsworth will.wadsworth...@gmail.com:
Hi.
I have just started learning Clojure and I am really enjoying
myself. However, I am still getting to grips with the workings of its
concurrency model, so please excuse me if my question seems too
obvious.
I have some code that reads data from a file, parses it and generates
a CSV file. The flow is as follows:
code
(use 'clojure.contrib.duck-streams)
(use 'clojure.contrib.pprint)
(defn parse-line [s]
(cl-format nil ~{\~A\~^,~} (into [] (.split s ;
(let [input-seq (for [line (read-lines input.dat)]
(parse-line line))]
(write-lines out.CSV input-seq))
/code
Now the question:
I would like to generate log entries for any malformed lines occurring
in the input file. Once of the ways might be to do this in parse-line
using clojure.contrib.loggingas follows:
code
(use 'clojure.contrib.logging)
(defn parse-line [s]
(let [cs (into [] (.split s ;))]
(if (= (count cs) 5)
(cl-format nil ~{\~A\~^,~} cs)
(error Incorrect number of columns in file.
/code
Since FOR returns a lazy sequence of the results, is this function
safe? (Seeing that it is not side-effect free?)
You have to acknowledge that the calls to parse-line will not
necessarily occur during the call to for, but maybe not before calling
write-lines, maybe partly if chunked-seqs are in play (sequences
preloading items in chunks of 32 items for example). And, if there is
an exception that is not thrown in write-lines, your logs may miss the
error logs for some of the remaining items not yet consumed by
write-lines.
s/if there is an exception that is not thrown in write-lines/if there is
an exception that *is* thrown in write-lines/
That is clear. Thanks.
While on the same topic: using read-lines on a large file (~80MB)
results
in an OutOfMemoryException. (I am running the JVM with -client rather
than
-server). To me, this is unexpected since read-lines lazily reads the
file
contents (and I also presume that the lines are not being cached in
memory).
Is there any way of being more memory efficient other than iteratively
reading
file contents using using .readLine?
BTW:
clojure.contrib.loggingindicates that it can use an agent for
logging. Is my assumption that invoking the logger (with or without
an agent) within a function would still mean that the function has
side-effects correct?
Technically speaking, yes. Imagine there's an I/O exception thrown
from theloggingcall (disk full, no write access, network access,
etc.), then your function would not be safe anymore.
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clojure.contrib.logging in side-effect free functions?
Hi.
I have just started learning Clojure and I am really enjoying
myself. However, I am still getting to grips with the workings of its
concurrency model, so please excuse me if my question seems too
obvious.
I have some code that reads data from a file, parses it and generates
a CSV file. The flow is as follows:
code
(use 'clojure.contrib.duck-streams)
(use 'clojure.contrib.pprint)
(defn parse-line [s]
(cl-format nil ~{\~A\~^,~} (into [] (.split s ;
(let [input-seq (for [line (read-lines input.dat)]
(parse-line line))]
(write-lines out.CSV input-seq))
/code
Now the question:
I would like to generate log entries for any malformed lines occurring
in the input file. Once of the ways might be to do this in parse-line
using clojure.contrib.logging as follows:
code
(use 'clojure.contrib.logging)
(defn parse-line [s]
(let [cs (into [] (.split s ;))]
(if (= (count cs) 5)
(cl-format nil ~{\~A\~^,~} cs)
(error Incorrect number of columns in file.
/code
Since FOR returns a lazy sequence of the results, is this function
safe? (Seeing that it is not side-effect free?)
BTW:
clojure.contrib.logging indicates that it can use an agent for
logging. Is my assumption that invoking the logger (with or without
an agent) within a function would still mean that the function has
side-effects correct?
Martin.
--
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