Update demos and adds <|

demos/interactionTrees/state.tri

@@ -0,0 +1,22 @@
+!import "../../lib/base.tri" !Local
+!import "../../lib/list.tri" !Local
+!import "../../lib/io.tri"   !Local
+
+-- Mutable state via get and put.
+--   get reads the current state.
+--   put replaces the state.
+--
+--   The CLI starts with an empty (Leaf) state.  This demo puts
+--   readable strings and prints them back out.
+
+main = io <|
+  bind (put "idle") (_ :
+  bind get (s1 :
+  bind (putStrLn (append "state: " s1)) (_ :
+  bind (put "running") (_ :
+  bind get (s2 :
+  bind (putStrLn (append "state: " s2)) (_ :
+  bind (put "done") (_ :
+  bind get (s3 :
+  bind (putStrLn (append "state: " s3)) (_ :
+  pure t)))))))))