It can be really tedious to list the cases where principal types do not exist. Haskell has a separate section for ambiguous overloading [1] for that reason, and

It can be really tedious to list the cases where principal types do not exist. Haskell has a separate section for ambiguous overloading [1] for that reason, and more ad-hoc or advanced type systems will be harder to describe. [1] https://www.haskell.org/onlinereport/haskell2010/haskellch4.html#x10-790004.3.4 https://www.haskell.org/onlinereport/haskell2010/haskellch4....