Why is Haskell irrelevant to the argument that LLMs can't reliably permute programming knowledge from one language to another? In fact, the purity of the language and dearth of training data seems like the perfect test case to see whether concepts found in more mainstream languages are actually understood.
Because human programmers routinely fail to do that too. Haskell is an obscure language that came out of academic research. Several of the core semantics (like lazyness by default) didn't get adopted anywhere else and are only found in Haskell.