palanquin scenario

data/scenarios/Challenges/_palanquin/emperor.sw

@@ -0,0 +1,78 @@
+def goDir = \f. \r.
+  let d = fst r in
+  if (d == down) {
+    grapesHere <- ishere "grapes";
+    if grapesHere {
+        grab; return ()
+    } {};
+    return ();
+  } {
+    turn d;
+
+    // An obstruction might arise after
+    // navigation direction is determined
+    // but before we move.
+    try {
+      move;
+    } {};
+    f;
+  }
+  end;
+
+def followRoute = \item.
+    nextDir <- path (inL ()) (inR item);
+    case nextDir return $ goDir $ followRoute item;
+    end;
+
+def getGrapes =
+    let targetItem = "grapes" in
+    emperorHasThem <- has targetItem;
+    if emperorHasThem {
+        say "Tally ho!";
+    } {
+        grapesDropped <- as base {
+            baseHasThem <- has targetItem;
+            return $ not baseHasThem;
+        };
+
+        if grapesDropped {
+            followRoute targetItem;
+        } {
+            wait 10;
+            getGrapes;
+        };
+    }
+    end;
+
+def avoidSides =
+
+    toLeft <- scan back;
+    case toLeft return (\_.
+        turn right;
+    );
+
+    toRight <- scan back;
+    case toRight return (\_.
+        turn left;
+    );
+
+    behind <- scan back;
+    case behind return (\_.
+        isBlocked <- blocked;
+        if isBlocked {} {move;}
+    );
+
+    watch forward;
+    watch back;
+    watch left;
+    watch right;
+    wait 1000;
+    end;
+
+def go =
+    getGrapes;
+    avoidSides;
+    go;
+    end;
+
+go;

data/scenarios/Challenges/_palanquin/solution.sw

@@ -0,0 +1,118 @@
+def doN = \n. \f. if (n > 0) {f; doN (n - 1) f} {}; end;
+
+def intersperse = \n. \f2. \f1. if (n > 0) {
+        f1;
+        if (n > 1) {
+            f2;
+        } {};
+        intersperse (n - 1) f2 f1;
+    } {};
+    end;
+
+def shiftRightForPush =
+    turn back;
+    move;
+    turn left;
+    move;
+    turn left;
+    end;
+
+/*
+Precondition:
+Positioned behind the wall, facing it, on the leftmost cell.
+*/
+def pushWall =
+    intersperse 3 shiftRightForPush push;
+    end;
+
+def moveToBackWall =
+    turn back;
+    doN 5 move;
+    turn right;
+    doN 2 move;
+    turn right;
+    end;
+
+def moveRightSide =
+    turn right;
+    push;
+    turn right;
+    move;
+    turn left;
+    move;
+    turn left;
+    doN 5 push;
+    turn right;
+    move;
+    turn left;
+    move;
+    turn left;
+    push;
+    end;
+
+def moveLeftSide =
+    doN 4 move;
+    turn left;
+    doN 5 move;
+    turn right;
+    push;
+    turn left;
+    move;
+    turn right;
+    move;
+    turn right;
+    doN 5 push;
+    turn left;
+    move;
+    turn right;
+    move;
+    turn right;
+    push;
+    end;
+
+def initialSetup =
+    turn south;
+    doN 3 move;
+    turn right;
+    move;
+    turn right;
+    end;
+
+def waitUntilGrapesGrabbed =
+    itemHere <- scan forward;
+    case itemHere return (\_.
+        watch forward;
+        wait 1000;
+        waitUntilGrapesGrabbed;
+    );
+    end;
+
+def placeGrapes =
+
+    doN 4 move;
+    place "grapes";
+    turn back;
+    move;
+    doN 2 push;
+    turn back;
+    doN 2 move;
+    waitUntilGrapesGrabbed;
+
+    turn back;
+    doN 4 move;
+    turn back;
+    doN 2 push;
+    end;
+
+def go =
+    placeGrapes;
+
+    // initialSetup;
+    // pushWall;
+    // moveToBackWall;
+    // pushWall;
+    // moveRightSide;
+    // moveLeftSide;
+    end;
+
+go;