Re: efficiency

I know what you mean. However, if you look at it, data Empty1 a = E1 is a datatype with one constructor, and that constructor takes no arguments. So this is in fact a "phantom" unit type. newtype Empty2 a = E2 () is in fact better than data EmptyBad a = EBad () because the constructor E will be optimised away, and the type will be share the representation of the unit type (). However, I don't see why Empty1 and Empty2 would differ in any way at all... In any reasonable implementation, they would have the same internal representation, right? Similarly, data Pair1 v w a = P1 (v a) (w a) is just a tuple type. It should be exactly the same as newtype Pair2 v w a = P2 (v a, w a) If someone can explain why they would be different, I'm all ears. By the way, I don't understand why Haskell98 provides both strictness flags and newtype declarations.... it seems to me that newtype M [a1 a2 ....] = MC (...) should be exactly the same as data N [b1 b2 ....] = NC !(...) If I'm not mistaken, any compiler too dumb to notice a datatype with only one constructor strict in its one argument is too dumb to use. Ketil's local user wrote:

Feuer asks about:

...

newtype Empty a = E ()

vs.

...

data Empty a = E

and

...

newtype Pair v w a = P (v a, w a)

vs.

...

data Pair v w a = P (v a) (w a)

...

I was wondering if anyone on this list knew of any reasons the types he chose would be more efficient than mine....

When recently reading the GHC docs, the chapter about profiling, I think, I came across something about this. From Chapter 6:

| 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

-kzm -- If I haven't seen further, it is by standing in the footprints of giants