New ranching scenario (#835)

Demo with:

    stack run -- --scenario Challenges/Ranching/gated-paddock --autoplay

The primary element of this scenario is "testing for a closed loop" in the objective condition.  As written, this test is performed every "tick", and introduces noticeable rendering lag at higher "ticks / s" speeds.

What may be better is for the player to "ask" for the condition to be checked, perhaps by standing somewhere specific, picking up a particular object, or even with `say "Ready!"`.

data/scenarios/Challenges/00-ORDER.txt

@@ -3,3 +3,4 @@ teleport.yaml
 2048.yaml
 hanoi.yaml
 Mazes
+Ranching

data/scenarios/Challenges/Ranching/00-ORDER.txt

@@ -0,0 +1 @@
+gated-paddock.yaml

data/scenarios/Challenges/Ranching/_gated-paddock/enclosure-checking.sw

@@ -0,0 +1,255 @@
+// Algorithm:
+// ----------
+// Maintain current direction until a wall is encountered.
+// Then enter "wall-following mode".
+// This mode presumes the wall is not a loop.
+// Wall-following mode exploits recursion to keep track of how many left turns were made
+// and then unwinds them again by ensuring each is paired with a right turn.
+// Once the recursion is fully unwound, the robot proceeds along its original direction
+// (though it may now be laterally displaced).
+//
+// (If it was a loop, then an "oriented breadcrumb" would need to be left.
+// The breadcrumb is oriented in case a single-width passage is backtracked
+// along the opposite wall.)
+
+/** A "gate" is walkable, so we need to supplement the "blocked" check with this function.
+Since fences are "unwalkable", they do not need to be mentioned in this function.
+*/
+def isFenced =
+    s <- scan forward;
+    return (
+        case s
+            (\_. false)
+            (\x. x == "gate")
+    );
+    end;
+
+def isBlockedOrFenced =
+    b <- blocked;
+    f <- isFenced;
+    return (b || f);
+    end;
+
+// Returns true if we've already placed two
+// breadcrumbs on a given tile, false otherwise.
+def leaveBreadcrumbs =
+
+    let bc1 = "fresh breadcrumb" in
+    let bc2 = "treaded breadcrumb" in
+
+    wasTraversedOnce <- ishere bc1;
+    if wasTraversedOnce {
+        _crumb <- grab;
+        make bc2;
+        place bc2;
+        return false;
+    } {
+        wasTraversedTwice <- ishere bc2;
+        if wasTraversedTwice {
+            return true;
+        } {
+            // Make sure nothing's in the way before we place
+            // our breadcrumb:
+            x <- scan down;
+            case x return (\y.
+                // If we're on a water tile, get rid of
+                // it with our special "drilling" recipe
+                if (y == "water") {
+                    drill down;
+                    // Nothing will remain on the ground.
+                    // after making the "steam" via
+                    // the drilling recipe.
+                } {
+                    grab;
+                    return ();
+                };
+            );
+
+            make bc1;
+            place bc1;
+            return false;
+        };
+    };
+    end;
+
+def goForwardToPatrol = \wasBlocked.
+    b <- isBlockedOrFenced;
+    if b {
+        turn left;
+        goForwardToPatrol true;
+        turn right;
+        goForwardToPatrol false;
+    } {
+        if wasBlocked {
+            isLoop <- leaveBreadcrumbs;
+            if isLoop {
+                fail "loop";
+            } {};
+        } {};
+        move;
+    };
+    end;
+
+/**
+There should only be one place in the
+code where an exception is thrown: that is,
+if a treaded breadcrumb is encountered.
+*/
+def checkIsEnclosedInner =
+    try {
+        goForwardToPatrol false;
+        // Water is the outer boundary
+        hasWater <- ishere "water";
+        if hasWater {
+            return false;
+        } {
+            checkIsEnclosedInner;
+        };
+    } {
+        return true;
+    };
+    end;
+
+def checkIsEnclosed =
+
+    // The "evaporator" drill is used
+    // to clear water tiles.
+    let specialDrill = "evaporator" in
+    create specialDrill;
+    install self specialDrill;
+
+    // NOTE: System robots can walk on water
+    // so we only need this if we want to
+    // demo the algorithm with a player robot.
+//    create "boat";
+//    install self "boat";
+
+    checkIsEnclosedInner;
+    end;
+
+def boolToInt = \b. if (b) {return 1} {return 0}; end;
+
+def countAdjacentBlockages =
+
+    turn left;
+    b1 <- isBlockedOrFenced;
+    c1 <- boolToInt b1;
+
+    turn left;
+    b2 <- isBlockedOrFenced;
+    c2 <- boolToInt b2;
+
+    turn left;
+    b3 <- isBlockedOrFenced;
+    c3 <- boolToInt b3;
+
+    turn left;
+    b4 <- isBlockedOrFenced;
+    c4 <- boolToInt b4;
+
+    return $ c1 + c2 + c3 + c4;
+    end;
+
+// Step forward, observing left and right.
+def observeLeftAndRight =
+    move;
+    turn left;
+    amBlockedLeft <- isBlockedOrFenced;
+    val1 <- boolToInt amBlockedLeft;
+
+    turn back;
+    amBlockedRight <- isBlockedOrFenced;
+    val2 <- boolToInt amBlockedRight;
+
+    turn right;
+    move;
+    return $ val1 + val2;
+    end;
+
+
+/** If the four cardinal directions have at most
+one blockage, then there will exist an orientation
+where both that direction and its opposite direction
+are clear.
+So we can step that direction, check to the left and
+right of us, then step in the opposite direction
+and do the same. This allows us to check the 4
+blocks that touch the corners of the center block.
+*/
+def countDiagonalBlockages =
+    // First, orient to the clear front-to-back path
+    amBlocked <- isBlockedOrFenced;
+    if amBlocked {turn left;} {};
+
+    // Second, step to both sides
+    fwdCount <- observeLeftAndRight;
+    backCount <- observeLeftAndRight;
+    return $ fwdCount + backCount;
+    end;
+
+def isStandingOnBridge =
+    onFence <- ishere "fence";
+    onGate <- ishere "gate";
+    if (onFence || onGate) {
+        adjCount <- countAdjacentBlockages;
+        if (adjCount > 1) {
+            return true;
+        } {
+            diagCount <- countDiagonalBlockages;
+            return $ (adjCount + diagCount) > 1;
+        };
+    } {return false};
+    end;
+
+def getValForSheepIndex = \predicateCmd. \i.
+    try {
+        // This will throw an exception if
+        // the sheep has already drowned.
+        r <- robotnumbered i;
+        didSucceed <- as r {predicateCmd};
+
+        boolToInt didSucceed;
+    } {
+        return 0;
+    }
+    end;
+
+/**
+There are 3 sheep.
+They have indices 1, 2, 3.
+(The base has index 0).
+
+THIS DOES NOT WORK!
+*/
+def countSheepWithRecursive = \predicateCmd. \i.
+
+    if (i > 0) {
+        val <- getValForSheepIndex predicateCmd i;
+        recursiveCount <- countSheepWithRecursive predicateCmd $ i - 1;
+        return $ val + recursiveCount;
+    } {
+        return 0;
+    }
+    end;
+
+
+def countSheepWith = \predicateCmd.
+
+    val1 <- getValForSheepIndex predicateCmd 1;
+    val2 <- getValForSheepIndex predicateCmd 2;
+    val3 <- getValForSheepIndex predicateCmd 3;
+    return $ val1 + val2 + val3;
+
+    end;
+
+
+justFilledGap <- as base {
+    isStandingOnBridge;
+};
+
+if (justFilledGap) {
+    enclosedCount <- countSheepWith checkIsEnclosed;
+    return $ enclosedCount >= 1;
+} {
+    return false;
+}