ocaml - Create a personal type with an Hashtbl as attribute

Question

I'm trying to create a type like this:

type variable {
  id: string;
  tipe: int
}

type dec {
   variables: variable list;
   parent: dec option
}

During the execution of my program, I need to have a list of dec and add to runtime the variables, but with the list, I can't do that as it is an immutable data structure.

I'm trying to change the implementation and use a hash map to store the variable, for example, I need to store the variables as a hashtable with (key: string and value: int) but I have no idea how to implement a hash map with OCaml inside the type declaration.

Answer 1

This is a record type where each value of the type contains a hash table. The hash table maps from string to int:

type dec = {
    variables: (string, int) Hashtbl.t;
    parent: dec option;
}

There are many other ways to set this up. In particular, this uses the generic (polymorphic) hash table interface. If you want more control over the behavior you can use the functorial interface (which allows you to specify your own comparison and hashing functions).