First post of the year! To talk about clojure, of course. I’ve written (pt_br) about clojure macros before. And yes, it is really powerful.
I’m using macros to help me setting up a connection with Amazon SimpleDB to do some small administrative tasks such as listing domains, creating domains, counting items in a domain, etc.
SimpleDB hasn’t a console, so you have interact with it using a pure html + js application provided by AWS, or do it by hand. I do prefer doing it by my own :). Then I created de following macro:
(defmacro boot-sdb []
'(do
(.setLevel (java.util.logging.Logger/getLogger "com.amazonaws")
java.util.logging.Level/WARNING)
(.setLevel (java.util.logging.Logger/getLogger "httpclient")
java.util.logging.Level/WARNING)
(.setLevel (java.util.logging.Logger/getLogger "org.apache.commons.httpclient")
java.util.logging.Level/WARNING)
(require (quote [cemerick.rummage :as sdb]))
(require (quote [cemerick.rummage.encoding :as enc]))
(use (quote apix.util))
(def *sdb* (sdb/create-client (env "AWS_KEYID") (env "AWS_KEY")))
(def *sdbconf* (assoc enc/keyword-strings :client *sdb*))
(println "Connected to SDB.")
(defn lsd [] (sdb/list-domains *sdbconf*))
(defn mkd [d] (sdb/create-domain *sdbconf* d))
(defn rmd [d] (sdb/delete-domain *sdbconf* d))
(defn countd [d] (str
(format "Total items [%s]: " d)
(:itemCount (sdb/domain-metadata *sdbconf* d))))
(defn sdb-help []
(println "Type '(lsd)' to list all domains")
(println "Type '(mkd domain-name)' to create a new domain")
(println "Type '(rmd domain-name)' to delete a domain")
(println "Type '(countd domain)' to get the items count of domain")
(println "Type '(sdb-help)' to see this help again"))
(sdb-help)))It saves the work of configuring the appropriate log levels as well as creating SimpleDB client using rummage (a SimpleDB client by @cemerick).
And why a macro? Because in some extent you can see a macro as a code template, just like Velocity or String Template. So what this macro does is just “typing” all this code on my REPL namespace, than the defined functions and vars are automatic available in the user namespace.
Using it is simple:
(use 'the.macro.namespace)
(boot-sdb)
Connected to SDB.
Type '(lsd)' to list all domains
Type '(mkd domain-name)' to create a new domain
Type '(rmd domain-name)' to delete a domain
Type '(countd domain)' to get the items count of domain
Type '(sdb-help)' to see this help again
nil(boot-sdb) “types” all the code for you, then you can call the functions like (lsd) to get the list of domains in your SimpleDB.
If take a closer look you may notice a function call to (env "AWS_KEYID"). It simply gets the environment variables set with your credentials.
You can extend the macro to have any admin task you may need. Note that the *sdbconf* will become available, so you can call rummage directly without having to configure all again.
That is it. Clojure is smart!