examples/: Add programs illustrating fork overloads

rt/examples/fork_variations.cpp

+#include <typon/typon.hpp>
+#include <typon/logger.hpp>
+
+
+using namespace typon;
+
+int fibo(int n) {
+  if (n < 2)
+    return n;
+  return fibo(n - 1) + fibo(n - 2);
+}
+
+Task<int> hello(int n) {
+  int r = fibo(30);
+  LOG("hello(%d)", n);
+  co_return r;
+}
+
+Join<void> parallel() {
+  LOG("Forked f = co_await fork(hello(10))");
+  Forked f = co_await fork(hello(1));
+
+  LOG("co_await fork(hello(10), {})");
+  co_await fork(hello(2), {});
+
+  // Careful! r must not be unwound before the fork finishes.
+  LOG("int r; co_await fork(hello(10), r)");
+  int r; co_await fork(hello(3), r);
+  // Sync to ensure the fork finished before r is unwound.
+  // Assuming there are no exceptions...
+  co_await Sync();
+}
+
+Root root() {
+  co_await parallel();
+}
+
+int main() {
+  root().call();
+  puts("done");
+  return 0;
+}

rt/examples/naive_fibonacci_fork_into.cpp

+#include <typon/typon.hpp>
+#include <cstdio>
+
+
+using namespace typon;
+
+Join<int> fibo(int n) {
+  if (n < 2) {
+    co_return n;
+  }
+  // Danger !
+  // The memory for a and b could be freed before the forks complete
+  int a; co_await fork(fibo(n - 1), a);
+  int b; co_await fork(fibo(n - 2), b);
+  // This sync() ensures that the forks complete before a and b are freed
+  // As long as there are no exceptions...
+  co_await Sync();
+  co_return a + b;
+}
+
+Root root() {
+  int result = co_await fibo(40);
+  printf("%d\n", result);
+}
+
+int main() {
+  root().call();
+  puts("done");
+  return 0;
+}