OCaml: get value's type name

Question

Is is possible to print value's name in OCaml, for example if I have

type my_type =
  | MyType_First of int
  | MyType_Second of string

and then do something like:

let my_value = MyType_First 0 in
print_string ("my_value is of type " ^ String.from_type my_value ^ ".\n";

can I get "my_value is of type MyType_First." ?

Thank you.

Answer 1

Monomorphic solution:

let from_type = function
  | MyType_First _ -> "MyType_First"
  | MyType_Second _ -> "MyType_Second"

Polymorphic solution: none. (AFAIK, lexical tokens corresponding to constructors are not recorded in the bytecode/binary, even when debugging flags are specified. The only thing one could do is to print the integer ‘identifier’ for the constructor, using some dark Obj.magic.)

Answer 2

What you want is a simpler form of generic print and is not available in OCaml as such, but some workarounds exist - e.g. deriving.