Cannot make recursive functions with optional arguments.

[smimram]

Consider the following code:

def rec fact(~n=0)
  if n == 0 then
    1
  else
    n * fact(n=(n-1))
  end
end

It gives rise to the error

Error 5: this value has type
  (n : _, ...) -> _ (inferred at line 7, char 8-13)
but it should be a supertype of the type of the value at line 3 char 0 - line 9 char 3
  (?n : _) -> _

because when the function fact is applied to the label n in the middle, we infer that it has a non-optional argument labeled n: we cannot guess that it is going to be optional yet...

This means in practice that we cannot make recursive functions with optional arguments (and I have more convincing examples than factorial...).

I don't see a way out without introducing a new syntax for using optional arguments when we really want to mean that they are optional. In OCaml, the way out is to use option types, which we don't have...

@toots any idea / comment ?

[smimram]

The way out consists in defining the function without optional arguments and the redefining it with optional arguments but this is not very clean...

[toots]

That's an interesting one.. I think that for now we're stuck with it. Let's keep an eye on it.

[smimram]

BTW, it turns out that this is working in OCaml, which means that some magic is at work :)

[toots]

Let's bring that to the magician @dbaelde..