Update demos and adds <|

demos/interactionTrees/forkAwait.tri

@@ -0,0 +1,18 @@
+!import "../../lib/base.tri" !Local
+!import "../../lib/list.tri" !Local
+!import "../../lib/io.tri"   !Local
+
+-- Basic fork and await.
+-- fork spawns a concurrent task and returns a handle.
+-- await blocks until the task completes and returns its value.
+
+worker = (msg :
+  bind (putStrLn (append "working: " msg)) (_ :
+  pure (append msg "-result")))
+
+main = io <|
+  (bind (fork (worker "job1")) (h1 :
+  bind (fork (worker "job2")) (h2 :
+  bind (await h1) (r1 :
+  bind (await h2) (r2 :
+  putStrLn (append "Got " (append r1 (append " and " r2))))))))