I previously asked this question, and after much investigation I concluded that there are special rules GHC applies only for infix $ and ..
For this question, I'm assuming that GHC follows the system mentioned on the RankNTypes - Haskell Prime page further elaborated in the arbitary-rank.
RankNTypes - Haskell Prime page states the following:
parameter variables without explicit signatures are assigned monotypes in upwards inference, but may inherit arbitrary-rank types in downwards checking.
I'm presuming "assigned monotypes" means that rank-N types are converted to rank-1 types by moving all their qualifiers to the outermost level.
I also believe this is what caused the unusual type error that led to me asking my previous question.
So I have a few questions:
1) Is there anyway to get GHC to warn (or error) on implicit conversion to monotypes? The type error in my previous question took a while to work out, a warning of a conversion to monotype would have been more helpful than a type error.
2) Are there cases where implicit "assigning to monotypes" is sensible behaviour, and if so, could you give an example?
3) Regarding infix $ and ., these seem to have special rules in GHC. Where is this documented? And are there any other special rules that GHC has, and where are they documented?
