add thread example

examples/07_Threads.mers

@@ -0,0 +1,33 @@
+is_prime := n -> {
+  0.1.sleep // wow, what an inefficient algorithm, oh no
+  d := 1
+  ().loop(() -> {
+    &d = (d, 1).sum
+    if d.lt(n) {
+      if n.modulo(d).eq(0) (false)
+    } else (true)
+  })
+}
+
+find_primes := start_at -> {
+  () -> (().loop(() -> {
+    out := if start_at.is_prime (start_at)
+    &start_at = (start_at, 1).sum
+    out
+  }))
+}
+
+primes_count := 0
+
+background_thread := {() ->
+  2.find_primes.take(20).map(p -> { &primes_count = (primes_count, 1).sum, p }).as_list
+}.thread
+
+// Show status to the user while the background thread works
+().loop(() -> {
+  0.2.sleep
+  (" Found ", primes_count, " primes...\r").concat.print
+  if background_thread.thread_finished (())
+})
+
+("\nPrimes: ", background_thread.thread_await).concat.println