New faults and syntax (#2034)

- Remove `[?]` syntax.
- Change `int!` to `int?` syntax.
- New `fault` declarations.
- Enum associated values can reference the calling enum.

resources/examples/contextfree/boolerr.c3

@@ -4,15 +4,8 @@ import libc;
 import std::io;
 import std::collections::maybe;
 
-fault TitleResult
-{
-	TITLE_MISSING
-}
-
-fault ReadError
-{
-	BAD_READ,
-}
+fault TITLE_MISSING;
+fault BAD_READ;
 
 struct Doc
 {
@@ -30,14 +23,14 @@ struct Summary
 	bool ok;
 }
 
-fn void! Summary.print(Summary* s, OutStream out)
+fn void? Summary.print(Summary* s, OutStream out)
 {
 	io::fprintf(out, "Summary({ .title = %s, .ok = %s})", s.title.get() ?? "missing", s.ok)!;
 }
 
-fn Doc! read_doc(String url)
+fn Doc? read_doc(String url)
 {
-	if (url.contains("fail")) return ReadError.BAD_READ?;
+	if (url.contains("fail")) return BAD_READ?;
 	if (url.contains("head-missing")) return { };
 	if (url.contains("title-missing")) return { .head = maybe::value{Head}({}) };
 	if (url.contains("title-empty")) return { .head = maybe::value{Head}({ .title = maybe::value{String}("")}) };
@@ -57,14 +50,14 @@ fn Summary read_and_build_summary(String url)
 	return build_summary(read_doc(url)) ?? {};
 }
 
-fn bool! is_title_non_empty(Doc doc)
+fn bool? is_title_non_empty(Doc doc)
 {
-	String! title = doc.head.get().title.get();
-	if (catch title) return TitleResult.TITLE_MISSING?;
+	String? title = doc.head.get().title.get();
+	if (catch title) return TITLE_MISSING?;
 	return title.len > 0;
 }
 
-fn bool! read_whether_title_non_empty(String url)
+fn bool? read_whether_title_non_empty(String url)
 {
     return is_title_non_empty(read_doc(url));
 }
@@ -90,7 +83,7 @@ fn void main()
             summary.print(out)!!;
             io::fprintn(out, "")!!;
             io::fprintf(out, "  Title: %s\n", summary.title.get() ?? "")!!;
-            bool! has_title = read_whether_title_non_empty(url);
+            bool? has_title = read_whether_title_non_empty(url);
             // This looks a bit less than elegant, but as you see it's mostly due to having to
             // use printf here.
             io::fprintf(out, "  Has title: %s vs %s\n", bool_to_string(has_title) ?? (@catch(has_title)).nameof, has_title ?? false)!!;

resources/examples/contextfree/cleanup.c3

@@ -6,12 +6,9 @@ struct Resource
 	String name;
 }
 
-fault Error
-{
-	WELCOME_TO_YOUR_DOOM
-}
+fault WELCOME_TO_YOUR_DOOM;
 
-fn Resource! resource_init(String name)
+fn Resource? resource_init(String name)
 {
 	io::printfn("open %s", name);
 	return { name };
@@ -19,7 +16,7 @@ fn Resource! resource_init(String name)
 
 fn void Resource.deinit(Resource this) => io::printfn("close %s", this.name);
 
-macro void! @open_with(String name; @body(Resource resource))
+macro void? @open_with(String name; @body(Resource resource))
 {
 	Resource resource = resource_init(name)!;
 	defer
@@ -30,7 +27,7 @@ macro void! @open_with(String name; @body(Resource resource))
 	@body(resource);
 }
 
-fn Resource! prep_out(String out_name, String[] prep_names)
+fn Resource? prep_out(String out_name, String[] prep_names)
 {
 	Resource writer = resource_init(out_name)!; // Rethrow the optional result
 	defer catch writer.deinit();
@@ -39,7 +36,7 @@ fn Resource! prep_out(String out_name, String[] prep_names)
 		@open_with(name; Resource reader)
 		{
 	        io::printfn("use %s", reader.name);
-	        // if (true) return Error.WELCOME_TO_YOUR_DOOM?;
+	        // if (true) return WELCOME_TO_YOUR_DOOM?;
 		}!;
 	}
 	return writer;

resources/examples/contextfree/guess_number.c3

@@ -11,27 +11,23 @@ struct Game
 	int high;
 }
 
-fault InputResult
-{
-	NOT_AN_INT,
-	FAILED_TO_READ,
-}
+fault NOT_AN_INT, FAILED_TO_READ;
 
 int err_count = 0;
 
-fn int! ask_guess(int high)
+fn int? ask_guess(int high)
 {
 	io::printf("Guess a number between 1 and %d: ", high);
-	String text = io::treadline() ?? InputResult.FAILED_TO_READ?!;
-	return text.to_int() ?? InputResult.NOT_AN_INT?;
+	String text = io::treadline() ?? FAILED_TO_READ?!;
+	return text.to_int() ?? NOT_AN_INT?;
 }
 
-fn int! ask_guess_multi(int high)
+fn int? ask_guess_multi(int high)
  {
 	while (true)
 	{
-		int! result = ask_guess(high);
-		if (@catch(result) == InputResult.NOT_AN_INT)
+		int? result = ask_guess(high);
+		if (@catch(result) == NOT_AN_INT)
 		{
 		  io::printn("I didn't understand that.");
 		  err_count++;
@@ -41,7 +37,7 @@ fn int! ask_guess_multi(int high)
 	}
 }
 
-fn void! Game.play(Game *game)
+fn void? Game.play(Game *game)
 {
 	while (!game.done)
 	{