Re: unsafeCoerce and type aliases under type applications

On 12/3/11 9:07 PM, Felipe Almeida Lessa wrote:

On Sat, Dec 3, 2011 at 5:39 PM, Joachim Breitner wrote:

...

have used unsafeCoerce to change the type inside a container to a "type" alias in real code, but your post makes me wonder: Under what circumstances is that safe? Is that documented somehow? Can a tool or the compiler decide for us whether it is safe?

AFAIK, newtypes are safe, and for everything else you're on your own. =)

N.B., newtypes are safe in the sense of congruent rewriting; i.e., if X is a newtype of Y, then we can rewrite X to Y (or Y to X) in any subterm of the type term (just like if X = Y or X ~ Y). It's not just at the top-level of the type term. -- Live well, ~wren