[RFC] Type of `return` is wrong

[Dave Clarke]

The type rule (and corresponding implementation) of the type of return is as follows:

     E |- expr : t
     E |- currentMethod : _ -> t
    -----------------------------
      E |- return expr : t

I argue that this is wrong, and the type should be unit or, even better, anything.

     E |- expr : t
     E |- currentMethod : _ -> t
    -----------------------------
      E |- return expr : t'

Consider the following example (out of context):

if foo then
    return 10
else
    this.skip()
end

where this.skip() has type unit.

This does not type check, even though the only one of the branches actually returns a result.

I would argue that making the type anything (which is probably Bottom in the current implementation) rather than unit will allow for more flexibility, permitting the following example to compile:

  def bar() : String
    "bar"
  end

  def foo() : Maybe[int]
    if true then
      return Nothing : Maybe[int]
    else
      this.bar()
    end
    Just(11)
  end

The fix should be easy, but I'm not sure what the consequence will be. My understanding is that Bottom type does not play nicely.

Similar comments apply to forward.