Try to deal with #46

[back2dos]

Seems to work fine as indicated by the tests. I'm slightly hesitant to add more implicit casts at this point, but this one seems specific enough.

Also, using GADTs is always fun until it isn't. In this case, postfix switch autocompletion fails:

Anyway, if people could confirm that this doesn't blow up everything else for them, I guess we can merge it.

[kevinresol]

The diff looks good in my codebase :+1:

[back2dos]

Well, seems to work fine for me, so let's do this.

[nadako]

Wow this is neat :) I'm also surprised that Haxe handles this pattern matching properly figuring out that there can be no Failed case.