The feature I most want from little languages like this is safety: in addition to restricting what it can do, I want to be able to take a snippet of untrusted code and execute it with a strict limit on how long it can take and how much memory it is allowed to use.

I want this so I can build features for end-users to provide snippets of code while knowing they won't be able to break anything, either accidentally or maliciously.

This is a surprisingly rare quality!

A common failure point here is allowing infinite loops ("while true") or allowing unbound mathematical operations, like powers or factorials of really large numbers.