add ex084 async

1 files changed, 56 insertions, 0 deletions

diff --git a/exercises/084_async.zig b/exercises/084_async.zig
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+++ b/exercises/084_async.zig
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+//
+// Six Facts:
+//
+// 1. The memory space allocated to your program for the
+// invocation of a function and all of its data is called a
+// "stack frame".
+//
+// 2. The 'return' keyword "pops" the current function
+// invocation's frame off of the stack (it is no longer needed)
+// and returns control to the place where the function was
+// called.
+//
+//     fn foo() void {
+//         return; // Pop the frame and return control
+//     }
+//
+// 3. Like 'return', the 'suspend' keyword returns control to the
+// place where the function was called BUT the function
+// invocation's frame remains so that it can regain control again
+// at a later time. Functions which do this are "async"
+// functions.
+//
+//     fn fooThatSuspends() void {
+//         suspend; // return control, but leave the frame alone
+//     }
+//
+// 4. To call any function in async context and get a reference
+// to its frame for later use, use the 'async' keyword:
+//
+//     var foo_frame = async fooThatSuspends();
+//
+// 5. If you call an async function without the 'async' keyword,
+// the function FROM WHICH you called the async function itself
+// becomes async! In this example, the bar() function is now
+// async because it calls fooThatSuspends(), which is async.
+//
+//     fn bar() void {
+//         fooThatSuspends();
+//     }
+//     
+// 6. The main() function cannot be async!
+//
+// Given facts 3 and 4, how do we fix this program (broken by facts
+// 5 and 6)?
+//
+const print = @import("std").debug.print;
+
+pub fn main() void {
+    foo();
+}
+
+fn foo() void {
+    print("foo() A\n", .{});
+    suspend;
+    print("foo() B\n", .{});
+}