"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, 69 insertions, 0 deletions

diff --git a/exercises/024_errors4.zig b/exercises/024_errors4.zig
new file mode 100644
index 0000000..560b129
--- /dev/null
+++ b/exercises/024_errors4.zig
@@ -0,0 +1,69 @@
+//
+// Using `catch` to replace an error with a default value is a bit
+// of a blunt instrument since it doesn't matter what the error is.
+//
+// Catch lets us capture the error value and perform additional
+// actions with this form:
+//
+//     canFail() catch |err| {
+//         if (err == FishError.TunaMalfunction) {
+//             ...
+//         }
+//     };
+//
+const std = @import("std");
+
+const MyNumberError = error{
+    TooSmall,
+    TooBig,
+};
+
+pub fn main() void {
+    // The "catch 0" below is just our way of dealing with the fact
+    // that makeJustRight() returns a error union (for now).
+    var a: u32 = makeJustRight(44) catch 0;
+    var b: u32 = makeJustRight(14) catch 0;
+    var c: u32 = makeJustRight(4) catch 0;
+
+    std.debug.print("a={}, b={}, c={}", .{ a, b, c });
+}
+
+// In this silly example we've split the responsibility of making
+// a number just right into four (!) functions:
+//
+//     makeJustRight()   Calls fixTooBig(), cannot fix any errors.
+//     fixTooBig()       Calls fixTooSmall(), fixes TooBig errors.
+//     fixTooSmall()     Calls detectProblems(), fixes TooSmall errors.
+//     detectProblems()  Returns the number or an error.
+//
+fn makeJustRight(n: u32) MyNumberError!u32 {
+    return fixTooBig(n) catch |err| {
+        return err;
+    };
+}
+
+fn fixTooBig(n: u32) MyNumberError!u32 {
+    return fixTooSmall(n) catch |err| {
+        if (err == MyNumberError.TooBig) {
+            return 20;
+        }
+
+        return err;
+    };
+}
+
+fn fixTooSmall(n: u32) MyNumberError!u32 {
+    // Oh dear, this is missing a lot! But don't worry, it's nearly
+    // identical to fixTooBig() above.
+    //
+    // If we get a TooSmall error, we should return 10.
+    // If we get any other error, we should return that error.
+    // Otherwise, we return the u32 number.
+    return detectProblems(n) ??? 
+}
+
+fn detectProblems(n: u32) MyNumberError!u32 {
+    if (n < 10) return MyNumberError.TooSmall;
+    if (n > 20) return MyNumberError.TooBig;
+    return n;
+}