So, the way Jelly parses its programs are different to the way APL parses them. The way the links are parsed depends on whether 1 or 2 arguments are provided
Each command has a fixed arity, so d is always dyadic, H is always monadic etc.
So the concept of a function switching between dyadic and monadic doesn't exist in Jelly
@cairdcoinheringaahing or more to the point, it's unexpected if you expect + to concatenate jelly strings, and expected if you expect it to vectorize over jelly lists and act on their non-list elements--in this case python strings
and then ofc that is still fucky with the length example because length will give 1 for anything that isn't a jelly list, even a non-singleton python string