You do not need to school me about why "for" is not pure functional - as soon as you understand that it is syntactic sugar, you are fine; IO is also impure, so if you insisting in purity then the only option is Haskell.

If you want to be pedantic, in functional programming there is no such a thing as "return value", as there is no such a thing as statement, only expressions. And expressions always _have_ values, they do not _return_ them.

I agree that SML is better for teaching than OCaml no doubt about it.

I mean, it is pointless to continue this conversation; you did not use SML for a long time - I did use it last time last year, and I can attest, it is extremely impractical compared to any other FP language today.