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.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?) > > 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/ > >> 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? > > Technically speaking, yes. Imagine there's an I/O exception thrown > from the logging call (disk full, no write access, network access, > etc.), then your function would not be "safe" anymore. > -- 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