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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