> user=> (defn if-a [a b] (if (a) (str a) (str b))) The problem is " (a) " - it tries to call a as a function, which throws NullPointer if a is nil. You meant:
> user=> (defn if-a [a b] (if a (str a) (str b))) mg On Tue, Aug 23, 2011 at 9:37 PM, Andrew Xue <[email protected]> wrote: > this doesn't work: > > user=> (defn if-a [a b] (if (a) (str a) (str b))) > #'user/if-a > user=> (if-a nil "b") > java.lang.NullPointerException (NO_SOURCE_FILE:0) > user=> (if-a "a" nil) > user=> java.lang.ClassCastException: java.lang.String cannot be cast > to clojure.lang.IFn (NO_SOURCE_FILE:0) > > this does work: > > user=> (defn if-a [a b] (if (identity a) (str a) (str b))) > #'user/if-a > user=> (if-a nil "b") > "b" > user=> (if-a "a" nil) > "a" > > > why is the identity function is needed? thanks > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to [email protected] > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to [email protected] Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/clojure?hl=en
