Sorry @jcalz, I was to answer you specifically yesterday but was too tired and simply forgot it.

Yes, what you mention on your comment is what I was after. Little I knew I was taking TS to it's pants, so I finally plan to settle on something like this:

[
  /* One entry */
  {
    string: 'foo',

    function_1 (x) {
      let ret : number = x;
      return (ret);
    },

    function_2 (x) {
      let ret: number = x;
      return (ret);
    }
  },

  /* Another entry */
  ...
]

This is a construction I've seen for example, in prosemirror's schema (except for mine's being inside an array). If that's also a problem I'll then reparent these with an object and get rid of the array altogether.

For those calling it laziness: I wouldn't have devoted a whole day to try to solve this if that was the particular case.

Well, thank you all for you time and you attention!