Hi,
2010/7/30 abhinav sarkar <[email protected]>
> Hi,
> I am just starting to learn Clojure by writing a small library. I came
> across a situation in which I have to parse a String for getting a Date. Now
> the string can be in one of the three formats. So I wrote this functions to
> parse it:
>
> (def #^{:private true :tag SimpleDateFormat} full-date-format
> (doto (SimpleDateFormat. "EEE, dd MMMM yyyy HH:mm:ss +0000")
> (.setTimeZone (TimeZone/getTimeZone "GMT"))))
>
> (def #^{:private true :tag SimpleDateFormat} date-format-wo-tz
> (doto (SimpleDateFormat. "EEE, dd MMMM yyyy HH:mm:ss")
> (.setTimeZone (TimeZone/getTimeZone "GMT"))))
>
> (def #^{:private true :tag SimpleDateFormat} short-date-format-wo-tz
> (doto (SimpleDateFormat. "dd MMM yyyy, HH:mm")
> (.setTimeZone (TimeZone/getTimeZone "GMT"))))
>
> (defn- parse-date [date-str]
> (if (some #(% date-str) [nil? blank?])
> nil
> (let [clean-date-str (trim date-str)]
> (try
> (.parse full-date-format clean-date-str)
> (catch java.text.ParseException e
> (try
> (.parse date-format-wo-tz clean-date-str)
> (catch java.text.ParseException e
> (.parse short-date-format-wo-tz clean-date-str))))))))
>
Just create an intermediate function which returns nil instead of throwing
an exception, and use some. Something like this (not tested):
(def #{:private true} parsers [full-date-format, date-format-wo-tz,
short-date-format-wo-tz])
(defn- parse-date [date-str]
(if (some #(% date-str) [nil? blank?])
nil
(let [clean-date-str (trim date-str)
parse-or-nil (fn [parser date-str] (try (.parse parser date-str)
(catch java.text.ParseException e nil)))]
(some #(parse-or-nil % clean-date-str) parsers))))
HTH,
--
Laurent
>
> I can't help but think that there must be a better way to do the same
> without so many nested try catch blocks. If this were Java, I could have
> looped over all the date formats and used an explicit return in the try
> block and continue in catch block. I don't understand how to do explicit
> return in Clojure.
>
> Also as the number of formats grows, I'll have to add more nested try catch
> blocks. Please suggest a cleaner way to do this.
>
> Regards,
> Abhinav
>
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