GADT Syntax for Haskell Type Definitions

From an exchange on the Haskell mailing list in October 2006:

Lennart Augustsson:

Well, I think the GADT type definition syntax is the syntax data type definitions should have had from the start. Too bad we didn't realize it 15 years ago.

Paul Hudak:

I agree! In my experience teaching Haskell, the current syntax is a bit confusing for newbies, and for years I've been telling students, "It really means this: ..." and then I write out a syntax more like GADT's.

I also think that if we had adopted this syntax from the beginning, GADT's would have been "discovered" far sooner than now.