Yes, that's what I had in mind. If only there was an effect system that could guarantee purity and at the same time not be in the way (i.e. allow full or Scala

Yes, that's what I had in mind. If only there was an effect system that could guarantee purity and at the same time not be in the way (i.e. allow full or Scala-like type inference). Then purity would be guaranteed by types, like it is in Haskell. (N.B. I'm not asking for Haskell's purity by default. I advocate impure as default, with a type guarantting purity.)