On May 4, 7:14 am, Laurent PETIT <laurent.pe...@gmail.com> wrote:
> Hi,
>
> 2009/5/4 Rich Hickey <richhic...@gmail.com>
>
>
>
>
>
> > On May 4, 1:53 am, Laurent PETIT <laurent.pe...@gmail.com> wrote:
> > > 2009/5/4 Christophe Grand <christo...@cgrand.net>
>
> > > > Janico Greifenberg a écrit :
> > > > > Hi,
>
> > > > > I encountered unexpected behavior of the 'if' form in clojure when
> > > > > using
> > > > > instances of java.lang.Boolean as the condition. I wanted to convert
> > > > > input strings to booleans and used the constructor of the Boolean
> > > > > class
> > > > > with the string parameter. However, when I pass these values as a
> > > > > condition to if, the true-branch always gets executed. For example:
>
> > > > > > (if (Boolean. "true") 1 2)
> > > > > 1
> > > > > > (if (Boolean. "false") 1 2)
> > > > > 1
>
> > > > > It seems to me that this has to do with the identity of the objects,
> > > > > as
> > > > > (Boolean. "false") is not identical (although equal) to the clojure
> > > > > literal false. Is this behavior intentional or a bug?
>
> > > > > The problem does not occur when I use Boolean/parseBoolean which
> > > > > returns
> > > > > a lower case boolean.
>
> > > > It's intentional, Rich said "for efficiency only canonic false is
> > > > logical false in
> > > > Clojure." inhttp://groups.google.com/group/clojure/msg/81ba3175da9a877c
>
> > > > Workaround:
> > > > > (if (boolean (Boolean. "false")) 1 2)
> > > > 2
>
> > > At the cost of a lesser experience concerning java interoperability, then
> > > ?
>
> > > Isn't that "premature optimization" ? ;-)
>
> > Not at all. The cost would apply to all usage of 'if' (i.e. all
> > conditionals).
>
> I don't know whether the impact would be that big, it was just a question.
>
> But whatever, shouldn't this be clearly stated in the documentation of
> the 'if' special form (http://clojure.org/special_forms#toc2) ?
>
Yes, I've enhanced the documentation here:
http://clojure.org/special_forms#if
Is that better?
Rich
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