Ocaml Phrasebook (part 6)

Ocaml is mostly assignment-free. This means that
a let creates a permanent (immutable) binding.

int x = 10;                      let x = 10 in
x = 11; /* assignment */         x = 11 (* boolean; false *)

If you want to use assignment, you need to explicitly
ask for a "reference" variable, which can have its value
accessed with ! or changed with :=

int x = 10;                      let x = ref 10 in
foo (x)                          foo (!x);
x = 11;                          x := 11

It is a little awkward, but it encourages you to isolate,
and understand, the state you use in a function. You tend
to need assignment a lot less than you'd assume.

Note: there are no "null" references. You cannot segfault.