"999 is enough for anybody" triple-zero padding (#18)

When I hit 999 exercises, I will finally have reached the ultimate
state of soteriological release and no more exercises will be needed.
The cycle will be complete. All that will be left is perfect quietude,
freedom, and highest happiness.

1 files changed, 46 insertions, 0 deletions

diff --git a/exercises/021_errors.zig b/exercises/021_errors.zig
new file mode 100644
index 0000000..cbb5ac8
--- /dev/null
+++ b/exercises/021_errors.zig
@@ -0,0 +1,46 @@
+//
+// Believe it or not, sometimes things go wrong in programs.
+//
+// In Zig, an error is a value. Errors are named so we can identify
+// things that can go wrong. Errors are created in "error sets", which
+// are just a collection of named errors.
+//
+// We have the start of an error set, but we're missing the condition
+// "TooSmall". Please add it where needed!
+const MyNumberError = error{
+    TooBig,
+    ???,
+    TooFour,
+};
+
+const std = @import("std");
+
+pub fn main() void {
+    var nums = [_]u8{ 2, 3, 4, 5, 6 };
+
+    for (nums) |n| {
+        std.debug.print("{}", .{n});
+
+        const number_error = numberFail(n);
+
+        if (number_error == MyNumberError.TooBig) {
+            std.debug.print(">4. ", .{});
+        }
+        if (???) {
+            std.debug.print("<4. ", .{});
+        }
+        if (number_error == MyNumberError.TooFour) {
+            std.debug.print("=4. ", .{});
+        }
+    }
+
+    std.debug.print("\n", .{});
+}
+
+// Notice how this function can return any member of the MyNumberError
+// error set.
+fn numberFail(n: u8) MyNumberError {
+    if (n > 4) return MyNumberError.TooBig;
+    if (n < 4) return MyNumberError.TooSmall; // <---- this one is free!
+    return MyNumberError.TooFour;
+}