RFC: match statement

[bolinfest]

As an initial attempt, I first made a small update to initially set a global in room02_bridge.esc:

:setup
# TODO: only set this if not yet set?
set_global r2_look_dialog_advance 0

which then makes the :look command in button.esc a bit cleaner when using the new match statement:

:look
>> r2_look_dialog_advance
	0 =>
		say player "That button must activate the bridge."
		inc_global r2_look_dialog_advance 1
	1 =>
		say player "I already said that this button must activate the bridge."
		inc_global r2_look_dialog_advance 1
	2 =>
		set_angle player 180
		say player "Listen closely."
		say player "This"
		say player "button"
		say player "must"
		say player "activate"
		say player "the bridge."
		inc_global r2_look_dialog_advance 1
	3 =>
		say player "I give up."
		say player "<sob>"

For the moment, to avoid introducing a new keyword (which would take away a possible command name), >> is used to indicate the start of a match statement. As you can see, the condition arms use a => syntax like Rust (and a number of other languages that support pattern matching).

Arguably, using a match statement avoids repeating the comparison valuable, eliminates the need for stop in many cases, and makes it easier to see that all cases are covered.

[bolinfest]

Admittedly, this is not "real" pattern matching. It's more of a glorified switch statement, but it's a start. Honestly, I didn't realize how flexible match is in GDScript today: https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_basics.html?highlight=match#match.

[balloonpopper]

Can we rename "arm" to something like "condition_option" please? It's not very intuitive.

[dploeger]

Or "branch".

[balloonpopper]

Assuming this gets the green light, please update the documentation as part of the PR.

[balloonpopper]

Also, is there any way to add conditional logic to this? i.e. issue 220

[StraToN]

Very good improvement to the language. I have nothing particular to add about it, apart that obviously documentation is required in the code and some TODOs need to be adresse.

Otherwise, great addition, thanks!

[dploeger]

Suggested change

	else:
	# TODO: error?
	pass

I'd simply remove this. match_lines.size() > 0 is really just a safety guard. If it really is empty, then we don't care.

[dploeger]

Please add a doc comment to this as well.

[dploeger]

Please add a doc comment

[dploeger]

This part actually should be put into is_valid I think.

[dploeger]

Or "branch".