Challenges tagged as decision-problem involve "deciding whether the input meets certain criteria". Although some challenges with this tag involve more than two categories, most involve only two categories, which seems to be the main purpose of the tag. This meta question refers to two-category decision problems only. The challenge is then equivalent to a question, such as "is the input number even?", and any possible input can be classified as "affirmative" if the answer is "yes", and "negative" if the answer is "no".
The purpose of this meta question is to decide a policy for the default options for output in two-category decision-problems. Having a default policy would be good, so that challenge writers don't need to state what is allowed as an output in every challenge. This related meta question asks what are some good options for challenge writers to use. Of course, answers to that meta question may be good answers for this one, but choosing the default options is a different matter, which deserves to be voted on separately.
Here are some possibilities regarding allowed outputs. This list is not meant to be exhaustive:
- "Consistent / consistent": Produce a consistent output (a number, a string, anything) for affirmative inputs, and a different, consistent output (again, it can be anything) for negative inputs. There are only two possible outputs.
- "Consistent / non-consistent": Produce a consistent output for affirmative inputs, and any other, non-consistent output for negative inputs. "Non-consistent" here means that each negative input can produce a different output.
- "Non-consistent truthy / non-consistent falsy": produce a non-consistent truthy output if the input is affirmative, and a non-consistent falsy output if it is negative. Each input produces a possibly different output.
- "Consistent truthy / consistent falsy": like 1, but in addition the consistent output for affirmative input must be truthy, and the consistent output for negative input must be falsy.
- "Non-consistent falsy / non-consistent truthy": like 3, but swapped. So an affirmative input produces any falsy output, and a negative input produces any truthy output.
Please post or vote answers to this meta question indicating which options should be the default for decision problems. Note that
- It probably makes sense to allow more than one options as default. For example, a proposed default rule might be to let answer writers choose between options 1 and 3 above. For clarity, each answer to this meta question should be self-contained, and state all the possibilities that are proposed as default policy.
- The default rules would only apply if the challenge doesn't specify otherwise. Of course, any challenge writer can override the default rules.
- "Truthy" and "falsy" are defined as usual.
- This meta question doesn't address output formats, whose general default rules are well established.