Please refer to this challenge on Sandbox.
The input is a black-box function, but as someone not knowing much of esolangs and golfing languages, I cannot even imagine how they accept black-box functions as input.
I can generalize this situation like the following: Mathematically, the input domain is not a discrete space. Examples, using topology terms:
The input is a function. In other words, the domain is a function space consisting of continuous functions, endowed with the compact-open topology.
The input is an iterator with no guarantee of terminating. In this case, the domain is a compactification of a discrete space with infinitely many points, resulting in a non-discrete space.
It already seems most esolangs cannot handle such inputs. For example, Brainfuck only handles user-inputted chars, and the space of strings is discrete.
Do black-box functions inevitably prohibit a class of languages from participating, or is there a workaround?