Question

I’m trying to write a polymorphic function, which needs to do something slightly different depending on the type of the parameter. Is there any way that I can do a pattern match on the type of the object, using the builtin types? I’m thinking of something along these lines:

let to_string v =
    match v with
    | string -> v
    | int -> string_of_int v
    | _ -> ""

but this doesn’t seem to be a valid OCaml program.

I have seen this question, but that doesn’t quite answer my question either. I would prefer to use the standard,builtin types rather than constructing new types for this (although I can do that if that is the only way).

Answer 1

Actually that answer completely applies to you. You can only match one type class, and the type defined by the union of int, string, float, … does not exist, and needs to be created (as in the previous answer). 'a operates on a particular type, but does not represent a union of all types.

You might be able to do what you want using an external C function (18.3), although, glancing at the atomic tags section, I’m not sure you’ll be able to differentiate char and int.