Re: efficiency

| Newtypes are better than datatypes: | | If your datatype has a single constructor with a single field, | use a newtype declaration instead of a data declaration. The newtype | will be optimised away in most cases

This feature is one I consider among the worst in Haskell. If a datatype with just a single constructor can be optimized away, why burden the programmer with such a task. It's easy for the compiler to filter out the data declarations having only one constructor and optimize them in the newtype way. I can't see any reasons not to do such data decl. optimization, but maybe I'm missing some point. Can anyone tell why this is up to the programmer, rather than the compiler?