Why do I need to repeat type declarations between interfaces and implementations (or how do I get around this)?

[jonathandoyle]

See also

What is the reason of separation of module implementation and signatures in OCaml?

What is the reason of the separation of module implementation and signatures? Wouldn’t it be better to describe signatures in function definitions? For example: let sum a:int b:int = a + b instead of: (* *.mli *) val sum : int -> int -> int (* *.ml *) let sum a b = a + b