I like to try and keep my level of nesting under control, and this
often involves hiding or re-structuring the let macro. The for macro
can implicitly assemble a let macro for you, but with a limitation
that the :let clause can't be first:
1:5 user=> (for [:let [z [:foo :bar]] x z] (name x))
java.lang.IllegalStateException: Can't pop empty vector (repl-1:5)
1:6 user=> (for [x [:foo :bar] :let [z (name x)]] z)
("foo" "bar")
1:7 user=>
Is this limitation intentional? Could the error message be improved?
Here's what I wanted to write:
(defn add-script-links-for-imported-javascript-libraries
[env dom-nodes]
(extend-dom dom-nodes [:html :head] :top
(template-for [:let [aggregation (-> env :cascade
:resource-aggregation)
libraries (@aggregation :libraries)]
asset-map libraries
:let [path (to-asset-path env asset-map)]]
:script { :type "text/javascript" :src path } [
linebreak ])))
(the formatting is probably scrambled)
But I had to juggle it to this:
(defn add-script-links-for-imported-javascript-libraries
[env dom-nodes]
(let [aggregation (-> env :cascade :resource-aggregation)
libraries (@aggregation :libraries)]
(extend-dom dom-nodes [:html :head] :top
(template-for [asset-map libraries
:let [path (to-asset-path env
asset-map)]]
:script { :type "text/javascript" :src path } [
linebreak ]))))
Of course there are any number of ways to write this, but I prefer the
first option, as it does less of a job of obscuring what the main
point of the function is: a call to extend-dom.
--
Howard M. Lewis Ship
Creator of Apache Tapestry
The source for Tapestry training, mentoring and support. Contact me to
learn how I can get you up and productive in Tapestry fast!
(971) 678-5210
http://howardlewisship.com
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