One of the hurdles in taking advantage of a data API, particularly the ever more popular RESTful APIs, is either in implementing or finding an existing implementation of the API in one's programming language of choice. (Of course this step isn't strictly necessary, but there are almost always advantages of having a complete implementation rather than hacking away with whatever one's favorite curl library might be).
Thanks to their high structure, one can often automatically generate such an implementation for SOAP-based APIs (e.g. R users might see the SSOAP package which does this).
I don't believe such a thing is inherently possible with RESTful APIs, but I understand one might be able to programmatically generate these functions if the RESTful API provided WADL documentation. (e.g. it seems there the omegahat project has a preliminary R package to do so). I am looking for examples of open data APIs that provide such WADL documentation. How common is this format? Is there a reason it is not more widely adopted? Are there convenient ways for API providers to generate WADL documentation without simply hand-coding the XML?