Martin Said:

Those two constructs are not the same

Compare

newtype T1 = C1 Bool data T2 = C2 !Bool

the difference is that the constructor C1 does not exist, so only the following values exist for T1:

C1 True (which is the represented as True) C1 False (which is the represented as False) C1 _|_ (which is represented as non-termination or error)

however, for T2, another value exist, namely _|_. So, pattern matching on (T2 x) may fail it the value is _|_. You are right that semantically newtype is the same as always matching lazily on the constructor.

The report says clearly that for a newtype like T1, C1 _|_ = _|_ This is the same as for T2 and C2. As for as I can tell, the only difference in the Report between a newtype and a tuple type with a completely strict constructor is in the rules for pattern matching. So I am trying to find someone who can explain the reason for the difference in the rules! I really want to know, because I think/hope that it will help me understand certain things about how to write efficient code.

The case for a tuple type (a,b,c) for instance, is different. Here there is a constructor, you can even type it by itself, it is (,,), try ":t (,,)" in hugs or ghci.

I don't understand what you're talking about here.... Of course there's a constructor... This message has been brought to you by the letter alpha and the number pi.