That’s not zero cost.
Presumably that function would be inlined?
When I want to constrain coerce, I usually resort to an auxiliary type family to guide the conversion. But I’m unsure about how to do it for newtypes in general 
That’s not zero cost.
Presumably that function would be inlined?
When I want to constrain coerce, I usually resort to an auxiliary type family to guide the conversion. But I’m unsure about how to do it for newtypes in general