clean up examples

Closes #325.

example/BFS-clear.sw

@@ -1,3 +1,7 @@
+// Quickly harvesting an entire forest in parallel using breadth-first
+// search, with robots spawning more robots.  Fun, though not very practical
+// in classic mode.
+
 def repeat : int -> cmd () -> cmd () = \n.\c.
   if (n == 0)
     {}

example/cat.sw

@@ -1,3 +1,6 @@
+// A "cat" that wanders around randomly.  Shows off use of the
+// 'random' command.
+
 let forever : cmd () -> cmd () = \c. c ; forever c in
 let repeat : int -> cmd () -> cmd () =
   \n. \c. if (n == 0) {} {c ; repeat (n-1) c} in

example/dfs.sw

@@ -0,0 +1,13 @@
+def ifC : forall a. cmd bool -> {cmd a} -> {cmd a} -> cmd a =
+  \test. \thn. \els. b <- test; if b thn els end
+
+// Recursive DFS to harvest a contiguous forest
+def dfs : cmd () =
+  ifC (ishere "tree") {
+    grab;
+    turn west;
+    ifC blocked {} {move; dfs; turn east; move};
+    turn north;
+    ifC blocked {} {move; dfs; turn south; move};
+  } {}
+end

example/fact.sw

@@ -1,7 +1,13 @@
-let repeat : int -> cmd () -> cmd () = \n.\c.
+// Defining simple recursive functions.
+
+def repeat : int -> cmd () -> cmd () = \n.\c.
   if (n == 0) {} {c ; repeat (n-1) c}
-in let fact : int -> int = \n:int.
+end
+
+def fact : int -> int = \n:int.
   if (n == 0)
     {1}
     {n * fact (n-1)}
-in move; move; repeat (fact 4) move
+end
+
+def gofar = repeat (fact 4) move end

example/rep.sw

@@ -1,7 +0,0 @@
-let rep : int -> cmd () -> cmd () =
-    \n.\c.
-      if (n == 0)
-        {}
-        {c ; rep (n-1) c}
-in
-  rep 10 move

example/square.sw

@@ -1,12 +0,0 @@
-let rep : int -> cmd () -> cmd () =
-    \n.\c.
-      if (n == 0)
-        {}
-        {c ; rep (n-1) c}
-in
-rep 4 (
-  rep 10 move;
-  turn left;
-  build {run("square.sw")};
-  return ()
-)

example/wander.sw

@@ -1,7 +1,12 @@
-let forever : cmd () -> cmd () =
-  \c. c ; forever c in
-forever (
-  b <- random 2;
-  turn (if (b == 0) {left} {right});
-  move
-)
+def forever : {cmd ()} -> cmd () =
+  \c. force c ; forever c
+end
+
+// Wander randomly forever.
+def wander : cmd () =
+  forever {
+    b <- random 2;
+    turn (if (b == 0) {left} {right});
+    move
+  }
+end

example/zigzag.sw

@@ -1,19 +0,0 @@
-let rep : int -> cmd () -> cmd () = \n. \c.
-  if (n == 0)
-    {}
-    { c; rep (n-1) c }
-in
-turn east;
-rep 50 (
-  grab; move;
-  turn left;
-  grab; move;
-  turn right;
-  p <- whereami;
-  let y = snd p in
-  if (y >= 10) {
-    turn right
-  } {
-    if (y <= 0) { turn left } {}
-  }
-)