Example use of fallback in placement room positions

src/Dodge/PlacementSpot.hs

@@ -37,6 +37,11 @@ unusedSpotAwayFromLink x = PSPos f (const id) Nothing
                 -> Just (PS p a,UsedSpot p a t)
         _       -> Nothing
 
+setFallback :: Placement -> Placement -> Placement
+setFallback fallback plmnt = plmnt
+    & plSpot . psFallback .~ Just fallback
+    & plIDCont %~ fmap (fmap $ setFallback fallback)
+
 unusedOffPathAwayFromLink :: Float -> PlacementSpot
 unusedOffPathAwayFromLink x = PSPos f (const id) Nothing
   where

src/Dodge/Room/Tanks.hs

@@ -36,12 +36,14 @@ tanksRoom crs its = do
     thetank <- randomTank <&> plSpot .~ unusedOffPathAwayFromLink 50
     let room = roomRectAutoLinks w h
         nwestlnks = length $ filter ((OnEdge West `S.member`) . _rlType) $ _rmLinks room
+    girderPosOrder <- shuffle [1 .. nwestlnks - 2]
     let plmnts = 
-            --[ twoRoomPoss (isUnusedLinkType (OnEdge West)) (isUnusedLinkType (OnEdge East)) $ \ps1 ps2 ->
-            [ twoRoomPoss (isUnusedLinkType (FromSouth i)) (isUnusedLinkType (FromSouth i)) $ \ps1 ps2 ->
+            --ok, this has become complicated
+            foldr1 setFallback [ twoRoomPoss (isUnusedLinkType (FromSouth i)) 
+                (isUnusedLinkType (FromSouth i)) $ \ps1 ps2 ->
                 sps0 $ PutShape $ girderV 96 20 10 (_psPos ps1) (_psPos ps2) 
-                | i <- [1 .. nwestlnks - 2]]
-            ++ map (\it -> sps0 (PutFlIt it) & plSpot .~ anyUnusedSpot) its
+                | i <- girderPosOrder]
+            : map (\it -> sps0 (PutFlIt it) & plSpot .~ anyUnusedSpot) its
             ++ map (\cr -> sps0 (PutCrit cr) & plSpot .~ unusedSpotAwayFromLink 50) crs
             ++ replicate ntanks thetank
 --            , sps0 $ PutShape $ colorSH orange $ pipePP 2 (V3 50 50 25) (V3 50 120 25)