GDScript functions with non-standard signatures

[Mercerenies]

GDLisp currently supports required arguments, optional arguments, and "rest" arguments. Putting aside the issue of named arguments (#55) for the moment, this means that, in GDLisp, the "correct" number of arguments with which to call a function is always a (potentially infinite) interval. A function like

(defn foo (a b &opt c d &rest e))

can be called with anywhere from 2 to infinity arguments. A function like

(defn foo (a b &opt c d))

can be called with anywhere from 2 to 4 arguments.

Unfortunately, a handful of GDScript built-in functions are not compatible with this interface.

• Rect2 takes two or four arguments
• Quat takes one, two, or four arguments
• Transform takes one, two, or four arguments
• Color takes one, three, or four arguments

How do we handle these?

[Mercerenies]

Current behavior is to just assume we have the right number of arguments. So, for instance, if you gave Rect2 three arguments, the fourth would get filled in with null automatically.

[Mercerenies]

Related note: We've encountered this problem with yield before (#5), which can take zero or two arguments. We didn't need to deal with it then because it turned out that yield made more sense as a special form (which can do its own ad-hoc validation of arguments at compile-time).