OCaml actually has correct block comments by his definition (and no line comments). This does lead to the odd fact that you can't have an unterminated string literal in a comment, which usually isn't a problem, but can be surprising.
21 karma · joined April 4, 2010
# let x = ref 0;;
val x : int ref = {contents = 0}
# let y = ref 0;;
val y : int ref = {contents = 0}
# if false then
x := 1;
y := 1;
;;
- : unit = ()
# (!x, !y);;
- : int * int = (0, 1)
# y := 0;;
- : unit = ()
# if false then
let z = 1 in
x := z;
y := z;
;;
- : unit = ()
# (!x, !y);;
- : int * int = (0, 0)Even without the purity question there are other things to consider. ML is evaluated strictly, for example. I don't know much Haskell but I don't believe it has any direct counterpart to ML's functors, either. There are probably many other differences. Haskell is definitely more popular and is still a niche language, so the reason you don't hear much about ML's benefits is probably just because it has so few users.