error handling kickoff

examples/programs/errors/main.bro

@@ -0,0 +1,82 @@
+BasicError :: enum {
+	bad
+	worse
+}
+
+DetailError :: union(enum) {
+	code i32
+	empty void
+}
+
+Left :: enum {
+	left
+}
+
+Right :: enum {
+	right
+}
+
+Both :: alias Left | Right
+
+BoxA :: union(enum) {
+	a i32
+}
+
+BoxB :: union(enum) {
+	b void
+}
+
+Box :: alias BoxA | BoxB
+
+maybe :: func(value i32) i32 ! BasicError {
+	if (value == 0) return .bad
+	return value + 1
+}
+
+via_try :: func(value i32) i32 ! BasicError {
+	unwrapped :: try maybe(value)
+	return unwrapped + 1
+}
+
+with_detail :: func(value i32) i32 ! DetailError {
+	if (value == 0) return DetailError{ code = 5 }
+	if (value == 1) return .empty
+	return value
+}
+
+pick :: func(value Both) i32 {
+	match value {
+		.left:  return 10
+		.right: return 20
+	}
+}
+
+payload :: func(value Box) i32 {
+	match value {
+		.a |n|: return n
+		.b:     return 3
+	}
+}
+
+main :: func() i32 {
+	acc i32 = 0
+
+	a :: maybe(0) catch 7
+	b :: maybe(4) catch 99
+	c :: via_try(3) catch 99
+	d :: via_try(0) catch 11
+	e :: with_detail(0) catch 13
+	f :: with_detail(2) catch 99
+
+	acc = acc + a + b + c + d + e + f
+	acc = acc + pick(.left)
+	r Right = .right
+	acc = acc + pick(r)
+	box BoxA = BoxA{ a = 8 }
+	acc = acc + payload(box)
+	empty BoxB = .b
+	acc = acc + payload(empty)
+
+	# 7 + 5 + 5 + 11 + 13 + 2 + 10 + 20 + 8 + 3 = 84
+	return acc - 84
+}