Thank you. doseq is probably more what I was looking for. I was
thinking mapcar when I used map, but I really don't want the resulting
seq anyway. I'll be a lot more careful about lazy evaluation, I'm
just not used to it. Again thanks for your response.
On May 30, 8:55 pm, Timothy Pratley <timothyprat...@gmail.com> wrote:
> Lazy evaluation strikes again! map doesn't actually do anything until
> you force it eg with dorun. This is quite a common mistake! Does
> anyone know how one would go able making a warning be printed when a
> lazy seq is created and thrown away without any evaluation? I'd be
> interested in implementing it with some pointers on where to start
> (I've read quite a lot of the code-base but well I'm not a language
> expert).
>
> To fix your problem:
>
> (let [b (new StringBuffer)]
> (dorun (map #(.append b (str % " ")) ["blah" "blah" "blah"]))
> b)
>
> I think it preferable to use doseq for side-effects:
> (let [b (new StringBuffer)]
> (doseq [s ["blah" "blah" "blah"]] (.append b (str s " "))
> b)
>
> Regards,
> Tim.
>
> On May 31, 10:47 am, Ben <ben.he...@gmail.com> wrote:
>
> > I'm not sure if this is an issue or not. I broke it down to a simple
> > case. When I pass a Java object into a map closure the object doesn't
> > seem to get updated:
>
> > (let [b (new StringBuffer)]
> > (map #(.. b (append (str % " "))) '("blah" "blah" "blah")) b) ;=>
> > #<StringBuffer >
>
> > expected ;=> #<StringBuffer blah blah blah >
>
> > I know it's doing working within map because if I take the ending b
> > off I get
>
> > (let [b (new StringBuffer)]
> > (map #(.. b (append (str % " "))) '("blah" "blah" "blah")))
>
> > ;=> (#<StringBuffer blah blah > #<StringBuffer blah blah blah >
> > #<StringBuffer blah blah blah >)
>
> > any ideas? Is this a bug or is this how it's supposed to work? I
> > realize there are better ways to do this, but I wanted to create a
> > simplified example of what I was noticing.
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