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 SierpiƄski 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?


1 Answer 1


It's not a issue if some languages can not participate in every challenge

There is a guideline not to exclude certain languages arbitrairly but if some language simply is unable to solve a challenge that is no reason not to pose the challenge.

Also, many esolangs do have a way to input a black box function, eg. as a string to be evaled

  • 4
    \$\begingroup\$ Writing a self-interpreter in brainfuck is a fun activity I encourage everyone to try at least once in their lifetime \$\endgroup\$
    – Jo King Mod
    Apr 19, 2023 at 11:51
  • 3
    \$\begingroup\$ You can also write a function if your esolang supports it that takes a function as input, not necessarily a full program. \$\endgroup\$
    – Seggan
    Apr 19, 2023 at 12:18

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