[dllthomas]

I find mtl pretty close to a sweet spot. The one thing I wish for is to be able to constrain effect order as a user (using your terminology above) when I'm writing code where one ordering or another is incorrect. The closest I can come is to fix the top of the stack, which suffices for correctness but puts some unnecessary burden on the consumer.

[tel]

My solution is to make a new typeclass which implies the order you demand. It'll all be social contract driven, but until we have dependent types one cannot ask for more.

[dllthomas]

Ah, good call!