A Lambda Web Service is something I doubt you have ever seen before, even though it is a highly interesting idea. It is a web service endpoint with “reversed responsibility." What I mean by that is that it’s not the job of the web service to provide the code it is executing, but rather the responsibility of the client. Hence, the web service endpoint is simply given some code, which it executes using an "eval" construct.
What? This Is Insecure and Dangerous!
No, in fact, it’s perfectly safe and secure! Depending upon which language you are using to implement the web service, and what constructs you have available in that language. I have created such a web service myself in Hyperlambda. It took me roughly 15-30 minutes, and it allows you to execute Hyperlambda on my server. Still, I doubt that you’d be able to execute malicious code since I use an overload of "eval" that allows me to use a (secure) subset of my server’s vocabulary of "functions" and "keywords."