I like PostgreSQL's SQL dialect. You can't treat non-bools as bools, but you can create casts yourself if you want to. Therefore if I want to cast a varchar a

I like PostgreSQL's SQL dialect. You can't treat non-bools as bools, but you can create casts yourself if you want to. Therefore if I want to cast a varchar as bool, I could decide what I mean by it and build the logic to do this. It would be preferable to do this with a domain though instead of a base type so as to avoid compatibility issues down the road.