Deriving sexp error

Learning
1

I have a simple module:

module Action = struct
    type t =
        | Increment
        | Update of int
    [@@deriving sexp]

    let should_log _t = true
end

Compilation results in “Error: Unbound value int_of_sexp”. The same code works in utop. Any idea what’s wrong with this syntax?

2

No syntax error, but you need to open Base to get the sexp converters for the base types. (You can also get them from Sexplib.)

2 Likes
3

Deriving sexp and compare are needed to get [%test_eq] to work. Lots of those details are missing in the RealWorldOCaml test chapter… It shows how to compare int list, but not a custom type.

4

I agree with this idea.
I want to know more about how to use custom types in [%test_eq].