[Haskell] Real life examples

[Ben Rudiak-Gould]

Lennart Augustsson wrote:

 > What do you mean when you say the interface is pure?
 >
 > If your module is really pure then there should be an implemenation
 > of it (which could have really bad complexity) with the same observable
 > behaviour that uses only pure Haskell.  Is this possible?

Really? I agree with the converse of that statement, but I don't think 
it goes both ways. To me a function or module is pure when you can use 
it without compromising the equational properties of the language. I 
don't think Data.Dynamic or Control.Monad.ST satisfy your criterion for 
purity, but I would call them pure (after discarding the functions 
marked unsafe in the latter).

-- Ben