Slim is a template language which I'd like to use in a client-side web app(which should be capable of working offline).
I wonder if I can use Opal to transpile it. If so, then how to do it?
And if it is impossible at the moment, could you please suggest what modifications should be made to Slim to make it Opal-compatible?
As suggested by max-pleaner in the comments, you should try with the opal-slim gem.