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.
At worst, the input has no guarantee of halting when evaluated, and if it halts, the evaluation result is to be discarded. In this case, the domain is the Sierpiński space, which is not Hausdorff.
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?
