World description DSL (#1376)

DSL for programming worlds, towards #1320 and #29 (and, indirectly, toward #50, since the world DSL should make a nice target for world saves) . Eventually this should be able to recreate all the world description/building features we have, though there is still a long way to go. But currently we can at least recreate the "classic" procedurally-generated world. I think this is a solid foundation we can merge as a first step, and then work on adding more features in subsequent PRs. Below are some notes that should help in reviewing. Note that the large number of files changed is due in large part to the elimination of the `default` field in scenario descriptions; see the "changed files" section below for an overview of the important/interesting changes. Issues split off from this one: #1394 #1395 #1396 #1397 Major changes ============ - New `data/worlds` subdirectory - All `.world` files are parsed at load time and saved in a `WorldMap` which gets threaded through, similar to `EntityMap` (perhaps we should think about passing around a single record instead) - Standard "classic" world - Used to be `testWorld2`, defined in Haskell code; now it is defined via the DSL in `worlds/classic.world`. This should make it much easier to experiment with variations. - We can now automatically extract entities mentioned in a world DSL term with `extractEntities`. There used to be an explicit list in `testWorld2Entities`, used to check pedagogy, generate documentation, etc., but it turns out it had (predictably) gotten out of date! This can't happen anymore. - It is now referenced in several tutorials (backstory, farming, world101, speedruns, etc.) - The `default` field of world descriptions is no more: one can use `dsl` to just specify a constant - Note in `Swarm.Game.State`, `dslWF` and `arrayWF` are combined using the `Monoid` instance to create `wf`. - `Erasable` - It used to be the case that if some kind of default terrain + entity was specified (e.g. stone + water), any `map` would completely override the default. However, we want to move towards combining everything with a `Monoid` instance. But by default this means the default entity would show through anywhere the `map` did not specify an entity. So we need a way to explicitly "erase" an entity from a lower layer. - If `e` is a `Semigroup`, then `Maybe e` is a `Monoid` where `Nothing` acts as an identity element. Likewise, `Erasable e` is a `Monoid` but adds two new elements: `ENothing` to be an identity, and `EErase` to be an *annihilator*. i.e. combining with `EErase` is like multiplying by zero. - We can now specify `erase` as an entity to override entity underneath. - There are several Haskell files with only changes related to `Erasable`, relating to e.g. the world editor, `PCells`, etc.; I'm not 100% sure I've always done the right thing here. DSL overview =========== - Integer, float, and Boolean literals. Note that `3` is *always* an `int`, and `3.0` is a `float`. It makes things much easier to not have to deal with `3` possibly being either `int` or `float`, though it does make things slightly more annoying for programmers. - Standard boolean, arithmetic, and comparison operators - `if ... then ... else ...` - `<>` operator for combining via `Semigroup` instance - Cell literals are enclosed in curly braces. Unlike the previous awkward world description syntax with one, two, or three-element lists denoting terrain, terrain + entity, or terrain + entity + robot, there can now be any number of elements in any order. - `{foo}` will be resolved as either terrain, an entity, or a robot, whichever is successful. So if the names are unambiguous one can just write `{tree}` or `{stone}`. - It is possible to explicitly indicate the type of cell value with syntax like `{entity: tree}` or `{terrain: stone}`. - Multiple items separated by commas is syntax sugar for combining with `<>`. e.g. `{tree, entity: boulder, stone} = {tree} <> {entity: boulder} <> {stone}`. - Ability to refer to the `seed` - Refer to the current `x` or `y` coordinates or the `hash` of the current coordinates - `let`-expressions for multiple variables: `let x1 = e1, x2 = e2, ... in ...` - `overlay [e1, e2, ...]` layers `e1` on the bottom, `e2` on top of that, etc., using the `Semigroup` instance for world functions - `"foo"` imports the DSL term in `worlds/foo.world` - `perlin` function to generate perlin noise - `mask` function to mask with a condition Changed files =========== - `Swarm.Util`: moved the `acquire` function here and gave it a more descriptive name. - `Swarm.Doc.Gen`: can now extract mentioned entities directly. - `Swarm.Game.Failure`: added new failure modes - `Swarm.Game.Scenario.Topography.WorldDescription`: get rid of `defaultTerrain` field, add `worldProg` for DSL. - `Swarm.Game.State`: see comment. - `Swarm.Game.World`: a bit of reorganization. Added a bunch of modules under this. - `Swarm.Game.World.Coords`: moved some code here from `Swarm.Game.World`. - `Swarm.Game.World.Gen`: moved some things here from `Swarm.Game.WorldGen` (also deleted a bunch of irrelevant code), and also added the `extractEntities` function to get all entities mentioned by a DSL term. - `Swarm.Game.World.Syntax`: raw, untyped syntax for world DSL terms. - `Swarm.Game.World.Parse`: parser for world DSL terms. Fairly standard. - `Swarm.Game.World.Typecheck`: takes raw, untyped terms produced by the parser and both typechecks and elaborates them into a simpler core language. An interesting feature is that the core language is *type-indexed*, so that the Haskell type system is actually ensuring that our typechecker is correct; every typechecked world DSL term value has a type which is indexed by a Haskell type corresponding to the type of the underlying DSL term. For example, `{entity: tree}` would have a type like `TTerm [] (World CellVall)` etc. Once terms make it through the typechecker, there cannot possibly be any bugs in the rest of the pipeline which would result in a crash, because the Haskell type system. (There could of course be *semantic* bugs.) Understanding exactly how the typechecker works is not too important. Of interest may be the `resolveCell` function, which determines how we decide what `Cell` is represented by a cell expression in curly braces. - `Swarm.Game.World.Abstract`: compile elaborated, typechecked world DSL terms down into an extremely simple core language with only constants and function application. This gives us very fast evaluation of world DSL terms. Understanding this module is not really necessary but there is a link to a blog post for those who are interested in how it works. - `Swarm.Game.World.Compile`: a further processing/compilation step after `Swarm.Game.World.Abstract`. Currently we don't actually use this, since it doesn't seem like it makes a big efficiency difference. - `Swarm.Game.World.Interpret`: interpreter for abstracted world DSL terms. - `Swarm.Game.World.Eval`: just puts together the pieces of the pipeline to evaluate a typechecked world DSL term. - `Swarm.Game.World.Load`: just loading world DSL terms from disk.
2024-10-03 19:17:31 +03:00 · 2023-08-17 06:08:42 -05:00 · 2023-08-17 06:08:42 -05:00 · 888ee44d18
commit 888ee44d18
parent 0179fa61b6
170 changed files with 2537 additions and 593 deletions
--- a/bench/Benchmark.hs
+++ b/bench/Benchmark.hs
@ -26,6 +26,7 @@ import Swarm.Language.Pipeline (ProcessedTerm)
 import Swarm.Language.Pipeline.QQ (tmQ)
 import Swarm.TUI.Model (gameState)
 import Swarm.TUI.Model.StateUpdate (classicGame0)
+import Swarm.Util.Erasable

 -- | The program of a robot that does nothing.
 idleProgram :: ProcessedTerm
@ -87,7 +88,7 @@ mkGameState robotMaker numRobots = do
    (mapM addTRobot robots)
    ( (initAppState ^. gameState)
        & creativeMode .~ True
-        & multiWorld .~ M.singleton DefaultRootSubworld (newWorld (WF $ const (fromEnum DirtT, Nothing)))
+        & multiWorld .~ M.singleton DefaultRootSubworld (newWorld (WF $ const (fromEnum DirtT, ENothing)))
    )

 -- | Runs numGameTicks ticks of the game.
--- a/data/scenarios/Challenges/2048.yaml
+++ b/data/scenarios/Challenges/2048.yaml
@ -179,7 +179,8 @@ robots:
      - [1, "1"]
 known: [water, wavy water, flower, tree]
 world:
-  default: [stone]
+  dsl: |
+    {stone}
  palette:
    "Ω": [grass, null, base]
    "┌": [stone, upper left corner]
--- a/data/scenarios/Challenges/Mazes/easy_cave_maze.yaml
+++ b/data/scenarios/Challenges/Mazes/easy_cave_maze.yaml
@ -65,7 +65,8 @@ entities:
    - The place you're trying to reach!  You win by executing `grab` on this item.
    properties: [known, portable]
 world:
-  default: [ice]
+  dsl: |
+    {ice}
  palette:
    'Ω': [stone, null, base]
    ' ': [stone, null]
--- a/data/scenarios/Challenges/Mazes/easy_spiral_maze.yaml
+++ b/data/scenarios/Challenges/Mazes/easy_spiral_maze.yaml
@ -65,7 +65,8 @@ entities:
    - The place you're trying to reach!  You win by executing `grab` on this item.
    properties: [known, portable]
 world:
-  default: [ice]
+  dsl: |
+    {ice}
  palette:
    'Ω': [stone, null, base]
    ' ': [stone, null]
--- a/data/scenarios/Challenges/Mazes/invisible_maze.yaml
+++ b/data/scenarios/Challenges/Mazes/invisible_maze.yaml
@ -65,7 +65,8 @@ entities:
    - The place you're trying to reach!  You win by executing `grab` on this item.
    properties: [known, portable]
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  palette:
    'Ω': [grass, null, base]
    '.': [grass, null]
--- a/data/scenarios/Challenges/Mazes/loopy_maze.yaml
+++ b/data/scenarios/Challenges/Mazes/loopy_maze.yaml
@ -58,7 +58,8 @@ entities:
    - The place you're trying to reach!  You win by executing `grab` on this item.
    properties: [known, portable]
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  palette:
    'Ω': [grass, null, base]
    '.': [grass, null]
--- a/data/scenarios/Challenges/Ranching/capture.yaml
+++ b/data/scenarios/Challenges/Ranching/capture.yaml
@ -140,7 +140,8 @@ entities:
    properties: [known]
 known: [flower, tree]
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  upperleft: [0, 0]
  offset: false
  palette:
--- a/data/scenarios/Challenges/Ranching/gated-paddock.yaml
+++ b/data/scenarios/Challenges/Ranching/gated-paddock.yaml
@ -506,14 +506,15 @@ seed: 0
 solution: |
  run "scenarios/Challenges/Ranching/_gated-paddock/fence-construction.sw"
 world:
-  default: [dirt, water]
+  dsl: |
+    {dirt, water}
  palette:
-    'B': [grass, null, base]
-    '.': [grass]
+    'B': [grass, erase, base]
+    '.': [grass, erase]
    't': [dirt, tree]
    'x': [stone, mountain]
    'c': [stone, cabin]
-    's': [grass, null, sheep]
+    's': [grass, erase, sheep]
    '%': [grass, clover, null]
    'H': [stone, pier, null]
    '~': [dirt, water]
--- a/data/scenarios/Challenges/Ranching/powerset.yaml
+++ b/data/scenarios/Challenges/Ranching/powerset.yaml
@ -179,7 +179,8 @@ entities:
    properties: [known, growable, portable]
 known: [sand]
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  upperleft: [-1, -1]
  offset: false
  palette:
--- a/data/scenarios/Challenges/Sliding
+++ b/data/scenarios/Challenges/Sliding
@ -721,7 +721,8 @@ recipes:
    time: 0
 known: []
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  upperleft: [-3, 2]
  offset: false
  palette:
@ -739,4 +740,4 @@ world:
    ..x....x..........
    ..xxxxxx..........
    ..................
-    zy................
+    zy................
--- a/data/scenarios/Challenges/Sokoban/Gadgets/no-reverse.yaml
+++ b/data/scenarios/Challenges/Sokoban/Gadgets/no-reverse.yaml
@ -66,12 +66,13 @@ entities:
    properties: [known, unwalkable, portable]
 known: [mountain, water, flower]
 world:
-  default: [grass, water]
+  dsl: |
+    {grass, water}
  upperleft: [-1, 1]
  offset: false
  palette:
-    'B': [grass, null, base]
-    '.': [grass]
+    'B': [grass, erase, base]
+    '.': [grass, erase]
    '@': [grass, monolith]
    'A': [grass, mountain]
    '*': [grass, flower]
--- a/data/scenarios/Challenges/Sokoban/Gadgets/one-way.yaml
+++ b/data/scenarios/Challenges/Sokoban/Gadgets/one-way.yaml
@ -49,12 +49,13 @@ entities:
    properties: [known, unwalkable, portable]
 known: [mountain, water, flower]
 world:
-  default: [grass, water]
+  dsl: |
+    {grass, water}
  upperleft: [-1, 1]
  offset: false
  palette:
-    'B': [grass, null, base]
-    '.': [grass]
+    'B': [grass, erase, base]
+    '.': [grass, erase]
    '@': [grass, monolith]
    'A': [grass, mountain]
    '*': [grass, flower]
--- a/data/scenarios/Challenges/Sokoban/Simple/trapdoor.yaml
+++ b/data/scenarios/Challenges/Sokoban/Simple/trapdoor.yaml
@ -101,13 +101,14 @@ entities:
    properties: [known, unwalkable, portable]
 known: [mountain, water, flower]
 world:
-  default: [grass, water]
+  dsl: |
+    {grass, water}
  upperleft: [-1, 1]
  offset: false
  palette:
-    'B': [ice, null, base]
-    '.': [grass]
-    'x': [dirt]
+    'B': [ice, erase, base]
+    '.': [grass, erase]
+    'x': [dirt, erase]
    '@': [grass, monolith]
    'A': [grass, mountain]
    '*': [grass, flower]
--- a/data/scenarios/Challenges/Sokoban/foresight.yaml
+++ b/data/scenarios/Challenges/Sokoban/foresight.yaml
@ -95,12 +95,13 @@ entities:
    properties: [known, unwalkable]
 known: [mountain, water, 3D printer, flower]
 world:
-  default: [grass, water]
+  dsl: |
+    {grass, water}
  upperleft: [-21, 10]
  offset: false
  palette:
-    'B': [ice, null, base]
-    '.': [grass]
+    'B': [ice, erase, base]
+    '.': [grass, erase]
    '*': [grass, flower]
    'b': [grass, boat]
    '3': [grass, 3D printer]
@ -108,8 +109,8 @@ world:
    'c': [grass, crate]
    'A': [grass, wall]
    'w': [dirt, water]
-    'x': [stone]
-    'z': [dirt]
+    'x': [stone, erase]
+    'z': [dirt, erase]
  map: |
    ..................3...A.
    .................AAAA.A*
--- a/data/scenarios/Challenges/arbitrage.yaml
+++ b/data/scenarios/Challenges/arbitrage.yaml
@ -378,7 +378,8 @@ recipes:
      - [1, drill]
 known: []
 world:
-  default: [dirt]
+  dsl: |
+    {dirt}
  upperleft: [0, 0]
  offset: false
  palette:
@ -413,4 +414,4 @@ world:
    ...X****7****1...
    ........*........
    B....p.p.p.p.p...
-    /.............../
+    /.............../
--- a/data/scenarios/Challenges/blender.yaml
+++ b/data/scenarios/Challenges/blender.yaml
@ -190,22 +190,23 @@ recipes:
 known: [water]
 seed: 0
 world:
-  default: [stone, water]
+  dsl: |
+    {stone, water}
  upperleft: [0, 0]
  offset: false
  palette:
    '0': [stone, water]
    '@': [stone, granite boulder]
-    '.': [grass]
-    'L': [stone]
+    '.': [grass, erase]
+    'L': [stone, erase]
    '>': [stone, bind gt]
    '=': [stone, bind eq]
-    H: [dirt]
+    H: [dirt, erase]
    A: [grass, water, ccw_robot]
    a: [grass, water, ccw_robot_down]
-    B: [grass, null, cw_robot]
-    b: [grass, null, cw_robot_down]
-    Ω: [grass, null, base]
+    B: [grass, erase, cw_robot]
+    b: [grass, erase, cw_robot_down]
+    Ω: [grass, erase, base]
    f: [stone, Amulet of Yoneda]
    x: [stone, locked door]
    k: [grass, door key]
@ -225,4 +226,4 @@ world:
    ..@@@@@@@@@.@@@@@@@.@@@@@@@.@..
    ..Ω.........@.....@.........@..
    @@@@@@@@@@@@@.>>=.@@@@@@@@@@@..
-    ...............................
+    ...............................
--- a/data/scenarios/Challenges/bridge-building.yaml
+++ b/data/scenarios/Challenges/bridge-building.yaml
@ -615,7 +615,6 @@ recipes:
 known: [water, sand, flower, iron mine]
 seed: 0
 world:
-  default: [blank]
  palette:
    '.': [blank]
    '/': [blank, left roof]
--- a/data/scenarios/Challenges/bucket-brigade.yaml
+++ b/data/scenarios/Challenges/bucket-brigade.yaml
@ -179,7 +179,8 @@ recipes:
 known: [boulder, lignite mine]
 seed: 0
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  palette:
    'B': [dirt, null, base]
    '.': [dirt]
--- a/data/scenarios/Challenges/chess_horse.yaml
+++ b/data/scenarios/Challenges/chess_horse.yaml
@ -34,10 +34,11 @@ robots:
      char: '♚'
 known: [water]
 world:
-  default: [ice, water]
+  dsl: |
+    {ice, water}
  palette:
-    '.': [grass]
-    '#': [ice]
+    '.': [grass, erase]
+    '#': [ice, erase]
    '┌': [stone, upper left corner]
    '┐': [stone, upper right corner]
    '└': [stone, lower left corner]
--- a/data/scenarios/Challenges/hackman.yaml
+++ b/data/scenarios/Challenges/hackman.yaml
@ -264,7 +264,6 @@ solution:
 known: []
 seed: 0
 world:
-  default: [blank]
  palette:
    'B': [blank]
    'Ω': [blank, null, base]
@ -307,4 +306,4 @@ world:
    x.....x....x....x.....x
    x.xxxxxxxx.x.xxxxxxxx.x
    x.....................x
-    xxxxxxxxxxxxxxxxxxxxxxx
+    xxxxxxxxxxxxxxxxxxxxxxx
--- a/data/scenarios/Challenges/hanoi.yaml
+++ b/data/scenarios/Challenges/hanoi.yaml
@ -155,7 +155,8 @@ known:
  - blocked two
  - blocked three
 world:
-  default: [grass, null]
+  dsl: |
+    {grass}
  palette:
    ',': [grass]
    '_': [stone]
--- a/data/scenarios/Challenges/ice-cream.yaml
+++ b/data/scenarios/Challenges/ice-cream.yaml
@ -206,7 +206,8 @@ recipes:
      - [1, scoop]
 known: []
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  upperleft: [0, 0]
  offset: false
  palette:
--- a/data/scenarios/Challenges/lights-out.yaml
+++ b/data/scenarios/Challenges/lights-out.yaml
@ -143,7 +143,6 @@ recipes:
    time: 0
 known: []
 world:
-  default: [blank]
  upperleft: [-1, 1]
  offset: false
  palette:
@ -160,4 +159,4 @@ world:
    .xxxxx.
    .xxxxx.
    z......
-    
+    
--- a/data/scenarios/Challenges/maypole.yaml
+++ b/data/scenarios/Challenges/maypole.yaml
@ -100,7 +100,8 @@ entities:
    properties: [known, unwalkable]
 known: [bitcoin]
 world:
-  default: [grass]
+  dsl: |
+    {grass}
  upperleft: [0, 0]
  offset: false
  palette:
--- a/data/scenarios/Challenges/teleport.yaml
+++ b/data/scenarios/Challenges/teleport.yaml
@ -56,15 +56,16 @@ robots:
      );
 known: [water, wavy water, flower, tree]
 world:
-  default: [ice, water]
+  dsl: |
+    {ice, water}
  palette:
    ',': [ice, water]
    ' ': [ice, water]
    '~': [ice, wavy water]
    '*': [grass, flower]
    'T': [grass, tree]
-    '.': [grass]
-    '_': [stone]
+    '.': [grass, erase]
+    '_': [stone, erase]
    '┌': [stone, upper left corner]
    '┐': [stone, upper right corner]
    '└': [stone, lower left corner]
--- a/data/scenarios/Challenges/wolf-goat-cabbage.yaml
+++ b/data/scenarios/Challenges/wolf-goat-cabbage.yaml
@ -98,7 +98,6 @@ entities:
 known: [water, boulder]
 seed: 0
 world:
-  default: [blank]
  palette:
    'A': [stone, boulder]
    'B': [stone, boulder, base]
@ -122,4 +121,4 @@ world:
    AAA~~~~~~~~~~~~~~~AAA
    AAAAA~~~~~~~~~~~AAAAA
    AAAAAAAA~~~~~AAAAAAAA
-    AAAAAAAAAAAAAAAAAAAAA
+    AAAAAAAAAAAAAAAAAAAAA
--- a/data/scenarios/Challenges/word-search.yaml
+++ b/data/scenarios/Challenges/word-search.yaml
@ -349,7 +349,8 @@ recipes:
      - [1, highlighter]
 known: [boulder]
 world:
-  default: [dirt]
+  dsl: |
+    {dirt}
  upperleft: [0, 0]
  offset: false
  palette:
--- a/data/scenarios/Fun/GoL.yaml
+++ b/data/scenarios/Fun/GoL.yaml
@ -58,7 +58,8 @@ robots:
        waitUntil (t <- time; return (mod t 0x20 == 0))
      )
 world:
-  default: [ice]
+  dsl: |
+    {ice}
  palette:
    'o': [ice, rock, cell]
    '.': [ice, null, cell]
--- a/data/scenarios/Fun/logo-burst.yaml
+++ b/data/scenarios/Fun/logo-burst.yaml
@ -56,7 +56,6 @@ robots:
  
 known: [boulder, tree, water, wavy water]
 world:
-  default: [blank]
  upperleft: [0, 0]
  offset: false
  palette:
--- a/data/scenarios/Mechanics/active-trapdoor.yaml
+++ b/data/scenarios/Mechanics/active-trapdoor.yaml
@ -55,14 +55,14 @@ solution: |
 known: [water, boulder, flower]
 seed: 0
 world:
-  default: [stone, water]
+  dsl: |
+    {stone, water}
  upperleft: [0, 0]
-  offset: false
  palette:
    '@': [stone, boulder]
-    '.': [grass]
-    G: [stone, null, gate]
-    Ω: [grass, null, base]
+    '.': [grass, erase]
+    G: [stone, erase, gate]
+    Ω: [grass, erase, base]
    f: [grass, flower]
  map: |
    .....
@ -78,4 +78,3 @@ world:
    .....
    ..Ω..
    .....
-  
--- a/data/scenarios/README.md
+++ b/data/scenarios/README.md
@ -26,7 +26,7 @@ request](https://github.com/swarm-game/swarm/blob/main/CONTRIBUTING.md)!
 The "blessed" scenarios that come with Swarm are stored in
 `data/scenarios` and can be accessed via the "New game" menu.
 However, other scenarios can be loaded directly from a file: simply
-run swarm with the `--scenario` flag (`-c` for short) and point it to
+run swarm with the `--scenario` flag (`-i` for short) and point it to
 a specific `.yaml` file containing a scenario.  For example:

 ```
@ -212,7 +212,6 @@ and `drill`.
 | `required` | `[]`     | `(int × string) list` | A list of catalysts required by the recipe.  They are neither consumed nor produced, but must be present in order for the recipe to be carried out.  It is a list of [count, entity name] tuples just like `in` and `out`.                                                                                                                                                                                              |
 | `time`     | 1        | `int`                 | The number of ticks the recipe takes to perform. For recipes which take more than 1 tick, the robot will `wait` for a number of ticks until the recipe is complete.  For example, this is used for many drilling recipes.                                                                                                                                                                                               |
 | `weight`   | 1        | `int`                 | Whenever there are multiple recipes that match the relevant criteria, one of them will be chosen at random, with probability proportional to their weights.  For example, suppose there are two recipes that both output a `widget`, one with weight `1` and the other with weight `9`.  When a robot executes `make "widget"`, the first recipe will be chosen 10% of the time, and the second recipe 90% of the time. |
-|            |          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                         |

 ### World

@ -220,14 +219,14 @@ The top-level `world` field contains a key-value mapping describing the
 world, that is, a description of the terrain and entities that exist
 at various locations.

-| Key          | Default? | Type          | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
-|--------------|----------|---------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| `default`    | `null`   | `string list` | A tuple representing the contents of a default cell (see [Cells](#cells), except that the default cell may not contain a robot).  If this key is present, it means that the whole world besides the part specified with the `map` will be filled with this default cell.  If omitted, the world besides the part specified with the `map` will be procedurally generated.                                                                                                                                        |
-| `offset`     | `False`  | `boolean`     | Whether the `base` robot's position should be moved to the nearest "good" location, currently defined as a location near a tree, in a 16x16 patch which contains at least one each of `tree`, `copper ore`, `bit (0)`, `bit (1)`, `rock`, `lambda`, `water`, and `sand`. The `classic` scenario uses `offset: True` to make sure that the it is not unreasonably difficult to obtain necessary resources in the early game.  See https://github.com/swarm-game/swarm/blob/main/src/Swarm/Game/WorldGen.hs#L204 . |
-| `scrollable` | `True`   | `boolean`     | Whether players are allowed to scroll the world map.                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
-| `palette`    | `{}`     | `object`      | The `palette` maps single character keys to tuples representing contents of cells in the world, so that a world containing entities and robots can be drawn graphically.  See [Cells](#cells) for the contents of the tuples representing a cell.                                                                                                                                                                                                                                                                |
-| `map`        | `""`     | `string`      | A rectangular string, using characters from the `palette`, exactly specifying the contents of a rectangular portion of the world.  Leading spaces are ignored.  The rest of the world is either filled by the `default` cell, or by procedural generation otherwise. Note that this is optional; if omitted, the world will simply be filled with the `default` cell or procedurally generated.                                                                                                                  |
-| `upperleft`  | `[0,0]`  | `int × int`   | A 2-tuple of `int` values specifying the (x,y) coordinates of the upper left corner of the `map`.                                                                                                                                                                                                                                                                                                                                                                                                                |
+| Key          | Default? | Type        | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
+|--------------|----------|-------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `dsl`        | `null`   | `string`    | An expression of the [Swarm world description DSL](../worlds/README.md).  If specified, this will be used as the base layer for the world.                                                                                                                                                                                                                                                                                                                                                                       |
+| `offset`     | `False`  | `boolean`   | Whether the `base` robot's position should be moved to the nearest "good" location, currently defined as a location near a tree, in a 16x16 patch which contains at least one each of `tree`, `copper ore`, `bit (0)`, `bit (1)`, `rock`, `lambda`, `water`, and `sand`. The `classic` scenario uses `offset: True` to make sure that the it is not unreasonably difficult to obtain necessary resources in the early game.  See https://github.com/swarm-game/swarm/blob/main/src/Swarm/Game/WorldGen.hs#L204 . |
+| `scrollable` | `True`   | `boolean`   | Whether players are allowed to scroll the world map.                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
+| `palette`    | `{}`     | `object`    | The `palette` maps single character keys to tuples representing contents of cells in the world, so that a world containing entities and robots can be drawn graphically.  See [Cells](#cells) for the contents of the tuples representing a cell.                                                                                                                                                                                                                                                                |
+| `map`        | `""`     | `string`    | A rectangular string, using characters from the `palette`, exactly specifying the contents of a rectangular portion of the world.  Leading spaces are ignored.  The rest of the world is either filled by the `default` cell, or by procedural generation otherwise. Note that this is optional; if omitted, the world will simply be filled with the `default` cell or procedurally generated.                                                                                                                  |
+| `upperleft`  | `[0,0]`  | `int × int` | A 2-tuple of `int` values specifying the (x,y) coordinates of the upper left corner of the `map`.                                                                                                                                                                                                                                                                                                                                                                                                                |

 #### Cells

--- a/data/scenarios/Speedruns/curry.yaml
+++ b/data/scenarios/Speedruns/curry.yaml
@ -33,5 +33,7 @@ robots:
      - [50, scanner]
      - [5, toolkit]
 world:
-  seed: null
  offset: true
+  scrollable: false
+  dsl: |
+    "classic"
--- a/data/scenarios/Speedruns/forester.yaml
+++ b/data/scenarios/Speedruns/forester.yaml
@ -33,5 +33,7 @@ robots:
      - [50, scanner]
      - [5, toolkit]
 world:
-  seed: null
  offset: true
+  scrollable: false
+  dsl: |
+    "classic"
--- a/data/scenarios/Speedruns/mithril.yaml
+++ b/data/scenarios/Speedruns/mithril.yaml
@ -33,5 +33,7 @@ robots:
      - [50, scanner]
      - [5, toolkit]
 world:
-  seed: null
  offset: true
+  scrollable: false
+  dsl: |
+    "classic"
--- a/data/scenarios/Testing/00-ORDER.txt
+++ b/data/scenarios/Testing/00-ORDER.txt
@ -37,6 +37,7 @@
 1256-halt-command.yaml
 1295-density-command.yaml
 1138-structures
+1320-world-DSL
 1356-portals
 144-subworlds
 1379-single-world-portal-reorientation.yaml
--- a/data/scenarios/Testing/1007-use-command.yaml
+++ b/data/scenarios/Testing/1007-use-command.yaml
@ -65,7 +65,6 @@ recipes:
      - [1, gate key]
 known: [flower]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/1024-sand.yaml
+++ b/data/scenarios/Testing/1024-sand.yaml
@ -37,7 +37,6 @@ robots:
      - solar panel
      - treads
 world:
-  default: [blank]
  palette:
    '>': [grass, null, base]
    'Å': [stone, copper mine]
--- a/data/scenarios/Testing/1034-custom-attributes.yaml
+++ b/data/scenarios/Testing/1034-custom-attributes.yaml
@ -179,7 +179,6 @@ entities:
    properties: [known]
 robots: []
 world:
-  default: [blank]
  palette:
    '.': [blank]
    '1': [blank, color1]
@ -207,4 +206,4 @@ world:
    .1234567..Rzzy...IIy
    .1234567y.R.z.......
    .abcdefg......C..BBz
-    .abcdefgyy.yy..Cz.z.
+    .abcdefgyy.yy..Cz.z.
--- a/data/scenarios/Testing/1138-structures/flip-and-rotate.yaml
+++ b/data/scenarios/Testing/1138-structures/flip-and-rotate.yaml
@ -8,7 +8,6 @@ robots:
    dir: [1, 0]
 known: [flower, bit (0), bit (1)]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    '*': [stone, flower]
--- a/data/scenarios/Testing/1138-structures/nested-structure.yaml
+++ b/data/scenarios/Testing/1138-structures/nested-structure.yaml
@ -8,7 +8,6 @@ robots:
    dir: [1, 0]
 known: [tree, flower, bit (0), bit (1)]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    '*': [stone, flower]
--- a/data/scenarios/Testing/1138-structures/sibling-precedence.yaml
+++ b/data/scenarios/Testing/1138-structures/sibling-precedence.yaml
@ -8,7 +8,6 @@ robots:
    dir: [1, 0]
 known: [water, sand]
 world:
-  default: [blank]
  palette:
    '.': [grass]
  upperleft: [-1, 1]
@ -86,4 +85,4 @@ world:
    ............
    ............
    ............
-    ............
+    ............
--- a/data/scenarios/Testing/1140-detect-command.yaml
+++ b/data/scenarios/Testing/1140-detect-command.yaml
@ -35,7 +35,6 @@ robots:
      - ADT calculator
 known: []
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/1157-drill-return-value.yaml
+++ b/data/scenarios/Testing/1157-drill-return-value.yaml
@ -22,7 +22,6 @@ robots:
      - ADT calculator
 known: []
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
@ -56,4 +55,4 @@ recipes:
    - [1, gumball]
    required:
    - [1, drill]
-    time: 1
+    time: 1
--- a/data/scenarios/Testing/1171-chirp-command.yaml
+++ b/data/scenarios/Testing/1171-chirp-command.yaml
@ -33,7 +33,6 @@ robots:
      - treads
 known: []
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/1171-resonate-command.yaml
+++ b/data/scenarios/Testing/1171-resonate-command.yaml
@ -37,11 +37,12 @@ robots:
      char: J
 known: []
 world:
-  default: [blank, boulder]
+  dsl: |
+    {blank, boulder}
  palette:
-    'Ω': [grass, null, base]
-    'J': [grass, null, judge]
-    '.': [grass]
+    'Ω': [grass, erase, base]
+    'J': [grass, erase, judge]
+    '.': [grass, erase]
  upperleft: [4, -1]
  map: |
   J........
--- a/data/scenarios/Testing/1171-sniff-command.yaml
+++ b/data/scenarios/Testing/1171-sniff-command.yaml
@ -42,7 +42,6 @@ robots:
      - treads
 known: []
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/1207-scout-command.yaml
+++ b/data/scenarios/Testing/1207-scout-command.yaml
@ -69,7 +69,6 @@ robots:
      attr: robot
 known: [tree, flower, boulder]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    'b': [grass, null, bot]
--- a/data/scenarios/Testing/1218-stride-command.yaml
+++ b/data/scenarios/Testing/1218-stride-command.yaml
@ -78,7 +78,6 @@ entities:
  capabilities: [movemultiple]
 known: [tree, flower, boulder, water]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/1234-push-command.yaml
+++ b/data/scenarios/Testing/1234-push-command.yaml
@ -51,7 +51,6 @@ entities:
  properties: [known, portable, unwalkable]
 known: [tree, flower, boulder, water]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    'j': [stone, null, judge]
--- a/data/scenarios/Testing/1256-halt-command.yaml
+++ b/data/scenarios/Testing/1256-halt-command.yaml
@ -41,7 +41,6 @@ robots:
      def forever = \c. c ; forever c end;
      forever ( turn right )
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '^': [grass, null, infinitebot]
--- a/data/scenarios/Testing/1295-density-command.yaml
+++ b/data/scenarios/Testing/1295-density-command.yaml
@ -35,7 +35,8 @@ robots:
      char: J
 known: []
 world:
-  default: [blank, boulder]
+  dsl: |
+    {blank, boulder}
  palette:
    'Ω': [grass, tree, base]
    'J': [grass, tree, judge]
--- a/data/scenarios/Testing/1320-world-DSL/00-ORDER.txt
+++ b/data/scenarios/Testing/1320-world-DSL/00-ORDER.txt
@ -0,0 +1,3 @@
+constant.yaml
+erase.yaml
+override.yaml
--- a/data/scenarios/Testing/1320-world-DSL/constant.yaml
+++ b/data/scenarios/Testing/1320-world-DSL/constant.yaml
@ -0,0 +1,23 @@
+version: 1
+name: Constant (uniform) world description
+description: |
+  Test that we can describe a uniform world by giving a
+  single cell value.
+objectives:
+  - condition: |
+      as base { n <- count "tree"; return (n >= 4) }
+    goal:
+    - Get 4 trees
+solution: |
+  grab; move; grab; move; grab; move; grab
+robots:
+  - name: base
+    loc: [0,0]
+    dir: [1,0]
+    devices:
+      - logger
+      - treads
+      - grabber
+world:
+  dsl: |
+    {terrain: ice} <> {entity: tree}
--- a/data/scenarios/Testing/1320-world-DSL/erase.yaml
+++ b/data/scenarios/Testing/1320-world-DSL/erase.yaml
@ -0,0 +1,30 @@
+version: 1
+name: Overlay with erasure
+description: |
+  Test that we can erase entities when overlaying
+objectives:
+  - condition: |
+      as base { n <- count "tree"; return (n == 0) }
+    goal:
+    - Get rid of your trees.
+solution: |
+  place "tree"; move; move;
+  place "tree"; move; move;
+  place "tree"; move; move;
+  place "tree"
+robots:
+  - name: base
+    loc: [0,0]
+    dir: [1,0]
+    devices:
+      - logger
+      - treads
+      - grabber
+    inventory:
+      - [4, tree]
+world:
+  dsl: |
+    overlay
+    [ {terrain: ice} <> {entity: tree}
+    , if (x + y) % 2 == 0 then {erase} else {blank}
+    ]
--- a/data/scenarios/Testing/1320-world-DSL/override.yaml
+++ b/data/scenarios/Testing/1320-world-DSL/override.yaml
@ -0,0 +1,25 @@
+version: 1
+name: Overlay with overriding
+description: |
+  Test that later entities override earlier ones when overlaying
+objectives:
+  - condition: |
+      as base { n <- count "tree"; return (n == 1) }
+    goal:
+    - Get a tree.
+solution: |
+  grab
+robots:
+  - name: base
+    loc: [0,0]
+    dir: [1,0]
+    devices:
+      - logger
+      - treads
+      - grabber
+world:
+  dsl: |
+    overlay
+    [ {terrain: ice} <> {entity: rock}
+    , {entity: tree}
+    ]
--- a/data/scenarios/Testing/1356-portals/automatic-waypoint-patrol.yaml
+++ b/data/scenarios/Testing/1356-portals/automatic-waypoint-patrol.yaml
@ -18,7 +18,6 @@ robots:
 known: [flower, boulder]
 world:
  upperleft: [-1, 1]
-  default: [blank]
  palette:
    '.': [grass]
    '*': [stone, flower]
--- a/data/scenarios/Testing/1356-portals/portals-and-waypoints.yaml
+++ b/data/scenarios/Testing/1356-portals/portals-and-waypoints.yaml
@ -32,7 +32,6 @@ robots:
 known: [tree, flower, sand, bit (0), bit (1)]
 world:
  upperleft: [-4, 7]
-  default: [blank]
  palette:
    '.': [grass]
    '*': [stone, flower]
--- a/data/scenarios/Testing/1356-portals/portals-flip-and-rotate.yaml
+++ b/data/scenarios/Testing/1356-portals/portals-flip-and-rotate.yaml
@ -50,7 +50,6 @@ robots:
      - treads
 known: [flower, bit (0), bit (1), bitcoin]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    '*': [stone, flower]
--- a/data/scenarios/Testing/201-require/201-require-device-creative.yaml
+++ b/data/scenarios/Testing/201-require/201-require-device-creative.yaml
@ -25,7 +25,6 @@ robots:
      - logger
 known: [water]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '~': [dirt, water]
--- a/data/scenarios/Testing/201-require/201-require-device-creative1.yaml
+++ b/data/scenarios/Testing/201-require/201-require-device-creative1.yaml
@ -26,7 +26,6 @@ robots:
    inventory:
      - [1, boat]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '~': [dirt, knownwater]
--- a/data/scenarios/Testing/201-require/201-require-device.yaml
+++ b/data/scenarios/Testing/201-require/201-require-device.yaml
@ -28,7 +28,6 @@ robots:
      - [1, treads]
 known: [water]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '~': [dirt, water]
--- a/data/scenarios/Testing/201-require/201-require-entities-def.yaml
+++ b/data/scenarios/Testing/201-require/201-require-entities-def.yaml
@ -30,7 +30,6 @@ robots:
      - [1, grabber]
      - [1, logger]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '┌': [stone, upper left corner]
--- a/data/scenarios/Testing/201-require/201-require-entities.yaml
+++ b/data/scenarios/Testing/201-require/201-require-entities.yaml
@ -28,7 +28,6 @@ robots:
      - [1, grabber]
      - [1, logger]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '┌': [stone, upper left corner]
--- a/data/scenarios/Testing/201-require/533-reprogram-simple.yaml
+++ b/data/scenarios/Testing/201-require/533-reprogram-simple.yaml
@ -46,7 +46,6 @@ robots:
      - [50, rock]
 known: [water]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '~': [dirt, water]
--- a/data/scenarios/Testing/201-require/533-reprogram.yaml
+++ b/data/scenarios/Testing/201-require/533-reprogram.yaml
@ -46,7 +46,6 @@ robots:
      - [50, rock]
 known: [water]
 world:
-  default: [blank, null]
  palette:
    '.': [grass]
    '~': [dirt, water]
--- a/data/scenarios/Testing/373-drill.yaml
+++ b/data/scenarios/Testing/373-drill.yaml
@ -40,10 +40,11 @@ robots:
      - [5, grabber]
 known: [water, wavy water]
 world:
-  default: [ice, water]
+  dsl: |
+    {ice, water}
  palette:
-    'Ω': [grass, null, base]
-    '.': [grass]
+    'Ω': [grass, erase, base]
+    '.': [grass, erase]
    ' ': [ice, water]
    '~': [ice, wavy water]
    'L': [grass, Linux]
--- a/data/scenarios/Testing/378-objectives.yaml
+++ b/data/scenarios/Testing/378-objectives.yaml
@ -46,7 +46,6 @@ robots:
      - [10, solar panel]
      - [0, harvester]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/394-build-drill.yaml
+++ b/data/scenarios/Testing/394-build-drill.yaml
@ -41,7 +41,6 @@ robots:
    inventory:
      - [1, detonator] # used to mark win
 world:
-  default: [blank]
  palette:
    '.': [grass]
    'M': [stone, mountain]
--- a/data/scenarios/Testing/397-wrong-missing.yaml
+++ b/data/scenarios/Testing/397-wrong-missing.yaml
@ -28,7 +28,6 @@ robots:
      - [1, treads]
      - [1, solar panel]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/428-drowning-destroy.yaml
+++ b/data/scenarios/Testing/428-drowning-destroy.yaml
@ -35,7 +35,6 @@ robots:
    program: "move"
 known: [water]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    ' ': [ice, water]
--- a/data/scenarios/Testing/475-wait-one.yaml
+++ b/data/scenarios/Testing/475-wait-one.yaml
@ -32,7 +32,6 @@ robots:
    program: |
      log "I shall sleep"; wait 1; log "I have awoken"
 world:
-  default: [blank]
  palette:
    '.': [grass]
    '┌': [stone, upper left corner]
--- a/data/scenarios/Testing/479-atomic-race.yaml
+++ b/data/scenarios/Testing/479-atomic-race.yaml
@ -77,7 +77,6 @@ entities:
      - You win!
    properties: [known, portable]
 world:
-  default: [blank]
  palette:
    '.': [grass]
  upperleft: [0,0]
--- a/data/scenarios/Testing/479-atomic.yaml
+++ b/data/scenarios/Testing/479-atomic.yaml
@ -59,7 +59,6 @@ entities:
    properties: [known, portable, growable]
    growth: [1,2]
 world:
-  default: [blank]
  palette:
    '.': [grass]
  upperleft: [0,0]
--- a/data/scenarios/Testing/490-harvest.yaml
+++ b/data/scenarios/Testing/490-harvest.yaml
@ -26,7 +26,6 @@ robots:
      - grabber
      - boat
 world:
-  default: [blank]
  palette:
    '.': [grass]
    'T': [stone, tree]
--- a/data/scenarios/Testing/504-teleport-self.yaml
+++ b/data/scenarios/Testing/504-teleport-self.yaml
@ -23,7 +23,6 @@ robots:
    inventory:
    - [1, tree]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    '┌': [stone, upper left corner]
--- a/data/scenarios/Testing/508-capability-subset.yaml
+++ b/data/scenarios/Testing/508-capability-subset.yaml
@ -37,9 +37,10 @@ robots:
      - [1, ADT calculator]
 known: [water]
 world:
-  default: [ice, water]
+  dsl: |
+    {ice, water}
  palette:
-    '.': [grass]
+    '.': [grass, erase]
    ' ': [ice, water]
    '┌': [stone, upper left corner]
    '┐': [stone, upper right corner]
--- a/data/scenarios/Testing/555-teleport-location.yaml
+++ b/data/scenarios/Testing/555-teleport-location.yaml
@ -24,4 +24,5 @@ robots:
    inventory:
      - [1, rock]
 world:
-  default: [grass, null]
+  dsl: |
+    {grass}
--- a/data/scenarios/Testing/562-lodestone.yaml
+++ b/data/scenarios/Testing/562-lodestone.yaml
@ -42,9 +42,10 @@ robots:
      - [0, bit (1)]
 known: [water, wavy water]
 world:
-  default: [ice, water]
+  dsl: |
+    {ice, water}
  palette:
-    '.': [grass]
+    '.': [grass, erase]
    ' ': [ice, water]
    '~': [ice, wavy water]
    'L': [grass, Linux]
@ -58,7 +59,7 @@ world:
    'A': [stone, magnetic vein]
    'o': [stone, lodestone]
    '0': [grass, bit (0)]
-    'B': [grass, null, base]
+    'B': [grass, erase, base]
  upperleft: [-1, 1]
  map: |
    ┌─────┐                                                                ~~
--- a/data/scenarios/Testing/684-swap.yaml
+++ b/data/scenarios/Testing/684-swap.yaml
@ -45,7 +45,6 @@ robots:
        )
      )
 world:
-  default: [blank]
  palette:
    '┌': [stone, upper left corner]
    '┐': [stone, upper right corner]
--- a/data/scenarios/Testing/687-watch-command.yaml
+++ b/data/scenarios/Testing/687-watch-command.yaml
@ -64,7 +64,6 @@ robots:
      doN 7 (move; wait 4; place "tree";);
 known: []
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    p : [grass, null, planter]
--- a/data/scenarios/Testing/699-movement-fail/699-move-blocked.yaml
+++ b/data/scenarios/Testing/699-movement-fail/699-move-blocked.yaml
@ -29,7 +29,6 @@ robots:
    program: |
      try {move} {say "Fatal error: two was unable to move into a boulder even though it is system robot!"}
 world:
-  default: [blank]
  palette:
    '@': [stone, boulder]
    'B': [grass, null, base]
--- a/data/scenarios/Testing/699-movement-fail/699-move-liquid.yaml
+++ b/data/scenarios/Testing/699-movement-fail/699-move-liquid.yaml
@ -35,7 +35,6 @@ robots:
    program: |
      try {move} {say "Fatal error: three was unable to move into water even though it is system robot!"}
 world:
-  default: [blank]
  palette:
    '~': [stone, water]
    'B': [grass, null, base]
--- a/data/scenarios/Testing/699-movement-fail/699-teleport-blocked.yaml
+++ b/data/scenarios/Testing/699-movement-fail/699-teleport-blocked.yaml
@ -33,7 +33,6 @@ robots:
    dir: [0,-1]
    system: true
 world:
-  default: [blank]
  palette:
    '@': [stone, boulder]
    'B': [grass, null, base]
--- a/data/scenarios/Testing/710-multi-robot.yaml
+++ b/data/scenarios/Testing/710-multi-robot.yaml
@ -23,7 +23,6 @@ objectives:
 solution: |
  move;move;move; move;move;move; move;move;move;
 world:
-  default: [blank]
  palette:
    '.': [blank]
    # FIRST ROOM
--- a/data/scenarios/Testing/795-prerequisite/795-prerequisite-and.yaml
+++ b/data/scenarios/Testing/795-prerequisite/795-prerequisite-and.yaml
@ -42,7 +42,6 @@ robots:
      - [2, board]
      - [5, rock]
 world:
-  default: [blank]
  palette:
    'x': [grass, null, base]
  upperleft: [0, 0]
--- a/data/scenarios/Testing/795-prerequisite/795-prerequisite-cycle-with-not.yaml
+++ b/data/scenarios/Testing/795-prerequisite/795-prerequisite-cycle-with-not.yaml
@ -34,7 +34,6 @@ robots:
      - [2, board]
      - [5, rock]
 world:
-  default: [blank]
  palette:
    'x': [grass, null, base]
  upperleft: [0, 0]
--- a/data/scenarios/Testing/795-prerequisite/795-prerequisite-mutually-exclusive.yaml
+++ b/data/scenarios/Testing/795-prerequisite/795-prerequisite-mutually-exclusive.yaml
@ -53,7 +53,6 @@ robots:
      - [2, board]
      - [5, rock]
 world:
-  default: [blank]
  palette:
    'x': [grass, flower, base]
  upperleft: [0, 0]
--- a/data/scenarios/Testing/795-prerequisite/795-prerequisite-or.yaml
+++ b/data/scenarios/Testing/795-prerequisite/795-prerequisite-or.yaml
@ -41,7 +41,6 @@ robots:
      - [2, board]
      - [5, rock]
 world:
-  default: [blank]
  palette:
    'x': [grass, flower, base]
  upperleft: [0, 0]
--- a/data/scenarios/Testing/858-inventory/858-counting-objective.yaml
+++ b/data/scenarios/Testing/858-inventory/858-counting-objective.yaml
@ -26,11 +26,10 @@ solution: |
  grab;
 known: [tree]
 world:
-  default: [blank]
  palette:
    'B': [grass, null, base]
    'w': [grass, tree]
  upperleft: [0, 0]
  map: |-
    w
-    B
+    B
--- a/data/scenarios/Testing/858-inventory/858-nonpossession-objective.yaml
+++ b/data/scenarios/Testing/858-inventory/858-nonpossession-objective.yaml
@ -25,7 +25,6 @@ solution: |
  place "tree";
 known: [tree]
 world:
-  default: [blank]
  palette:
    'B': [grass, null, base]
    'w': [grass]
--- a/data/scenarios/Testing/858-inventory/858-possession-objective.yaml
+++ b/data/scenarios/Testing/858-inventory/858-possession-objective.yaml
@ -23,11 +23,10 @@ solution: |
  grab;
 known: [tree]
 world:
-  default: [blank]
  palette:
    'B': [grass, null, base]
    'w': [grass, tree]
  upperleft: [0, 0]
  map: |-
    w
-    B
+    B
--- a/data/scenarios/Testing/920-meet.yaml
+++ b/data/scenarios/Testing/920-meet.yaml
@ -32,7 +32,6 @@ robots:
  - name: other
    dir: [1,0]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    'Ω': [grass, null]
--- a/data/scenarios/Testing/955-heading.yaml
+++ b/data/scenarios/Testing/955-heading.yaml
@ -17,7 +17,6 @@ robots:
      - treads
      - compass
 world:
-  default: [blank]
  palette:
    '^': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/956-GPS.yaml
+++ b/data/scenarios/Testing/956-GPS.yaml
@ -47,7 +47,6 @@ robots:
      y <- random 11;
      teleport base (x-5, y-5)
 world:
-  default: [blank]
  palette:
    '.': [grass]
  upperleft: [-5, 5]
--- a/data/scenarios/Testing/958-isempty.yaml
+++ b/data/scenarios/Testing/958-isempty.yaml
@ -39,7 +39,6 @@ entities:
    - A thing that everyone needs!
    properties: [portable]
 world:
-  default: [blank]
  palette:
    '.': [grass]
    '>': [grass, tree, base]
--- a/data/scenarios/Testing/961-custom-capabilities.yaml
+++ b/data/scenarios/Testing/961-custom-capabilities.yaml
@ -32,7 +32,6 @@ robots:
      - [1, wheels]
      - [1, solar panel]
 world:
-  default: [blank]
  palette:
    'Ω': [grass, null, base]
    '.': [grass]
--- a/data/scenarios/Testing/_Validation/1221-duplicate-entities.yaml
+++ b/data/scenarios/Testing/_Validation/1221-duplicate-entities.yaml
@ -15,7 +15,6 @@ entities:
    description:
      - Your scooter
 world:
-  default: [blank]
  palette:
    'x': [grass, null, base]
  upperleft: [0, 0]
--- a/data/scenarios/Testing/_Validation/1356-ambiguous-portal-entrance.yaml
+++ b/data/scenarios/Testing/_Validation/1356-ambiguous-portal-entrance.yaml
@ -30,7 +30,6 @@ robots:
 known: [tree]
 world:
  upperleft: [-1, 1]
-  default: [blank]
  palette:
    '.': [grass]
    'B': [grass, null, base]
--- a/data/scenarios/Testing/_Validation/1356-ambiguous-portal-exit.yaml
+++ b/data/scenarios/Testing/_Validation/1356-ambiguous-portal-exit.yaml
@ -30,7 +30,6 @@ robots:
 known: [tree]
 world:
  upperleft: [1, -1]
-  default: [blank]
  palette:
    '.': [grass]
    'B': [grass, null, base]
--- a/data/scenarios/Testing/_Validation/1356-waypoint-uniqueness-enforcement.yaml
+++ b/data/scenarios/Testing/_Validation/1356-waypoint-uniqueness-enforcement.yaml
@ -20,7 +20,6 @@ robots:
 known: [tree]
 world:
  upperleft: [1, -1]
-  default: [blank]
  palette:
    '.': [grass]
    'B': [grass, null, base]
--- a/Show More
+++ b/Show More