parse-or-nil can be avoided by calling parse with an additional
argument (ParsePosition. 0), in which case parse returns nil on
failure.
On Jul 30, 6:21 am, Laurent PETIT <laurent.pe...@gmail.com> wrote:
> Hi,
>
> 2010/7/30 abhinav sarkar <abhinav.sar...@gmail.com>
>
>
>
>
>
> > 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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