Question

From what I can tell, = and != is supposed to work on strings in OCaml. I’m seeing strange results though which I would like to understand better.

When I compare two strings with = I get the results I expect:

# "steve" = "steve";;
- : bool = true
# "steve" = "rowe";;
- : bool = false

but when I try != I do not:

# "steve" != "rowe";;
- : bool = true
# "steve" != "steve";; (* unexpected - shouldn't this be false? *)
- : bool = true

Can anyone explain? Is there a better way to do this?

Answer 1

!= is not the negation of =. <> is the negation of = that you should use:

# "steve" <> "rowe" ;;
- : bool = true
# "steve" <> "steve" ;;
- : bool = false
# 

!= is the negation of ==, and if you are an OCaml beginner, you should not be using any of these two yet. They can be a little tricky, and they are officially underspecified (the only guarantee is that if two values are == they are =).