There are some katas out there that require very specific theoretical knowledge (that is very unlikely to discover on your own) with little to no room for creativity/variance in solution.

But this is not one of them.

I solved it just by tinkering in GHCi and making up different theories and without looking up external resources. My solution isn't most canonical and I don't have a hard proof that it 100% correct (test cases are rather strong though so it probably is). You do have to be comfortable with prime numbers though (Spoiler!) but that's not a sacred knowledge.

Not an issue. By your logic

1. Every kata's description is insufficient because there always exist some people who do not have domain specific techniques (protip: coding is one) to solve the problem
2. Every kata must include spoilers and outline steps to solve them

which honestly doesn't hold any water. If you don't like certain katas, just don't do them okay?

not even close to an issue. Closing.

FYI, generic message:

Seems you're "rather new" to cw, so here are some general guidelines about the comments:

• Issue: problem in the kata itself (description, wrong tests, wrong internal solution...)
• Suggestions: well, I guess that part is clear
• Question anything else that is related to you having a problem solving a kata -> that's you, currently.

When you post issues:

• provide ALL the useful information:
  • language
  • input
  • outputs (actual expected) when relevant
  • error message when relevant
• check, DOUBLE check that this IS an issue, meaning that the problem is in the kata itself and not in your code. If it's in your code, post rather a question
• if you pass this step, you still have to prove/explain what the issue is (and if you can provide fixes, it's even better)

When you post a question: well, most of the above apply too x)

When you post code, use proper github markdown, so that it's readable.

I don't think this is a clear signal. I did some edits to description though, hope it is more strict now.

Let me quote the description: "only space, tabulation and linefeed are meaningful characters ... for the purposes of this simple kata, please do not add any other characters in the output".

Please show me where "the spec specifially mentions we can use [space] etc.", I'll correct this.

I am sorry if example cases somehow caused you to believe you can actually use placeholders instead of actual characters. Example test cases are not designed to do full tests on your code, but rather provide you with a starting point so that you can add your tests if needed. If you have any suggestions how to reduce ambiguity that confused you, e.g. edits for description or Example cases, I'll be glad to see those and implement them if feasible. Meanwhile, I am marking this issue as resolved.