Brian Hulley wrote:
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.
There's no mystery. The + operator used in that example
does not obey '1+1=2'.
-- Lennart
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
