Greetings list,

 

I've been trying to make object methods that return polymorphic variants, but it looks a bit stricter than I'm used to.

For example, take the following methods:

 

method private method_12 = function

| 1 -> `One

| _ -> `Two

 

method method_123 = function

| 3 -> `Three

| x -> self#method_12 x

 

method method_124 = function

| 4 -> `Four

| x -> self#method_12 x

 

This returns the type:

method private method_12 : int -> ([ > `Four | `One | `Three | `Two ] as 'a)

method method_123 : int -> 'a

method method_124 : int -> 'a

 

and complains that method_123 uses 'a, which is undefined. That's fair enough, since it's an open type in a non-private method.

However, if I give method_123 or method_124 a closed type signature it will give the same exact type to the other two methods.

 

What I really want is a signature like this:

method private method_12 : int -> [ > `One | `Two ]

method method_123 : int -> [ `One | `Two | `Three ]

method method_124 : int -> [ `One | `Two | `Four ]

 

If I replace method_12 with a function outside the class it works fine, but for whatever reason method_12 really wants to be the exact same type as method_123 and method_124.

 

Is there any way around this typing requirement for methods?

 

 

Thanks for any help,

Reed Wilson

 

 

PS. I'd rather avoid doing any verbose "post-processing" of the method_12 result, like this:

method_123 = function

| 3 -> `Three
| x -> (match self#method_12 with `One -> `One | `Two -> `Two)

 

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