Does DAML Repl support multi-line inputs

If I want to define a function using do notation, how do I do that?

At the moment, there is no option for multi-line inputs. What you can do is to define it on a single line with lines separated by ;, So something like:

do p <- allocateParty "p"; submit p (createCmd (T p))

Fully agree, that we should support some kind of multiline input.