Here is an example of using this:
(--> "hello world" (.toUpperCase _) (.toLowerCase _) (.indexOf _ "w"))
On Tue, Jul 5, 2011 at 3:50 PM, Asim Jalis <asimja...@gmail.com> wrote:
> Frequently I want to use the thread macros (-> or ->>) except I need
> to thread the arguments into positions other than the first and the
> last. Or sometimes I have to go back and forth between first and last
> positions. Instead of alternating between -> and ->> and creating
> nesting, I've been using this thread macro which replaces underscore
> with the value of the previous expression.
>
> (defmacro -->
> "Threads the expr through the forms. Replaces all underscores (_)
> with x in the form, making a list of it if it is not a list already.
> If there are more forms, inserts the first form as the last item in
> second form, etc."
> ([x form] (if (seq? form)
> (with-meta `(~(first form) ~@(replace {'_ x} (next
> form))) (meta form))
> (list form x)))
> ([x form & more] `(--> (--> ~x ~form) ~@more)))
>
> Is there a reason something like this does not exist in clojure.core?
> Is this an oversight or is there a reason this is not there?
>
> Asim
>
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