I would assume that this problem is an instance of the case documented here: <https://nim-lang.org/docs/manual.html#overload-resolution-lazy-type-resolution-for-untyped>
Overloads which require that the type of a parameter is known trigger the resolution of that argument leading to the error message you received. There have however been attempts to improve this situation in the past (such as <https://github.com/nim-lang/RFCs/issues/402>).
