Greg Buchholz wrote:
Hmm. It must be a little more complicated than that, right? Since after all you can print out *some* functions. That's what section 5 of _Fun with Phantom Types_ is about. Here's a slightly different example, using the AbsNum module from...
http://www.haskell.org/hawiki/ShortExamples_2fSymbolDifferentiation
import AbsNum
f x = x + 2 g x = x + 1 + 1
y :: T Double y = Var "y"
main = do print (f y) print (g y)
...which results in...
*Main> main (Var "y")+(Const (2.0)) (Var "y")+(Const (1.0))+(Const (1.0))
...is this competely unrelated?
Interesting! Referential transparency (as I understand it) has indeed been violated. Perhaps the interaction of GADTs and type classes was not sufficiently studied before being introduced to the language. So I'm now just as puzzled as you. Thanks for this example, Brian.