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══════════════════ Conversation compacted · ctrl+o for history ═════════════════

> /compact 
  ⎿  Compacted (ctrl+o to see full summary)
  ⎿  Referenced file PLAN.md
  ⎿  Read options.m (448 lines)
  ⎿  Read ../../../../../tmp/hex_large.svg (40 lines)
  ⎿  Read ../../../../../tmp/sq_test.svg (24 lines)
  ⎿  Referenced file render.m

> Let's do a thorough review of our code for clarity and modularity. Think 
deeply about any ways in which we might avoid duplication, encapsulate 
design decisions, or simplify the interfaces. 

● I'll do a thorough review of the codebase. Let me start by reading the key
   modules to understand the current structure.

● Search(pattern: "*.m", path: "~/Documents/projects/amaze")
  ⎿  Found 17 files (ctrl+o to expand)

● Read(grid.m)
  ⎿  Read 227 lines

● Read(maze.m)
  ⎿  Read 262 lines

● Read(boundary.m)
  ⎿  Read 296 lines

● Read(render.m)
  ⎿  Read 799 lines

● Let me continue reading the remaining modules to get a complete picture.

● Read(generate.m)
  ⎿  Read 84 lines

● Read(amaze.m)
  ⎿  Read 139 lines

● Read(generate.dfs.m)
  ⎿  Read 121 lines

● Read(generate.kruskal.m)
  ⎿  Read 183 lines

● Read(generate.prim.m)
  ⎿  Read 168 lines

● Read(generate.hunt_and_kill.m)
  ⎿  Read 191 lines

● Read(generate.aldous_broder.m)
  ⎿  Read 132 lines

● Read(generate.wilson.m)
  ⎿  Read 210 lines

● Read(generate.binary_tree.m)
  ⎿  Read 109 lines

● Read(generate.sidewinder.m)
  ⎿  Read 161 lines

● Read(check.m)
  ⎿  Read 125 lines

● Read(dump.m)
  ⎿  Read 113 lines

● Now I have a complete picture of the codebase. Let me provide a thorough
  review:

  ---
  Code Review: Clarity, Modularity, and Refactoring Opportunities

  1. Duplicated choose_random predicate (High Priority)

  The identical choose_random/4 predicate is defined in 6 different modules:
  - generate.dfs.m:104-116
  - generate.prim.m:151-163
  - generate.hunt_and_kill.m:174-186
  - generate.aldous_broder.m:115-127
  - generate.wilson.m:193-205
  - generate.kruskal.m (as part of shuffle logic)

  Recommendation: Extract this to a shared utility module (e.g.,
  random_util.m or add to generate.m interface).

  ---
  2. Duplicated neighbour-filtering predicates (High Priority)

  Several variations of "get valid neighbours" exist:

  | Module                   | Predicate              | Purpose
            |
  |--------------------------|------------------------|---------------------
  ----------|
  | generate.dfs.m           | unvisited_neighbours/3 | Neighbours not in
  visited set |
  | generate.prim.m          | valid_neighbours/2     | Neighbours in maze
  bounds     |
  | generate.hunt_and_kill.m | unvisited_neighbours/3 | Neighbours not in
  visited set |
  | generate.hunt_and_kill.m | visited_neighbours/3   | Neighbours already
  visited    |
  | generate.aldous_broder.m | all_neighbours/2       | All neighbours in
  maze bounds |
  | generate.wilson.m        | all_neighbours/2       | All neighbours in
  maze bounds |

  Recommendation: Add these to maze.m interface:
  :- func valid_neighbours(maze, cell) = list(cell).           % All 
  in-bounds neighbours
  :- func filter_neighbours(maze, set(cell), cell) = list(cell). % Generic 
  filter

  ---
  3. Duplicated shuffle logic (Medium Priority)

  generate.kruskal.m contains a full Fisher-Yates shuffle implementation
  (lines 134-178). This could be useful elsewhere.

  Recommendation: Extract to random_util.m or a dedicated shuffle.m module.

  ---
  4. Hex geometry duplication in render.m (Medium Priority)

  The hex corner offsets are computed repeatedly throughout render.m:
  - hex_edge_endpoints/8 (lines 416-464)
  - hex_edge_start_point/6 (lines 600-662)
  - hex_edge_end_point/6 (lines 715-759)
  - render_hex_background_polygon/4 (lines 261-291)

  All these compute Sf / 2.0, Sf * sqrt3 / 2.0, Sf, etc.

  Recommendation: Define corner positions once and reference them:
  :- type hex_corner ---> right ; upper_right ; upper_left ; left ;
  lower_left ; lower_right.
  :- pred hex_corner_offset(float::in, hex_corner::in, float::out,
  float::out) is det.

  Then define edges as pairs of corners.

  ---
  5. wall_corner_point is unused indirection (Low Priority)

  render.m:542-545:
  wall_corner_point(Topology, Bounds, S, M, Wall) =
      wall_start_point(Topology, Bounds, S, M, Wall).

  This function just forwards to wall_start_point. Consider removing it.

  ---
  6. Inconsistent handling of invalid topology/direction combinations

  Some predicates return dummy values (0.0, 0.0) for invalid cases, while
  others call unexpected/2:

  Dummy values (silent failure):
  - wall_start_point for hex directions with square topology (lines 574-582)
  - wall_end_point for hex directions with square topology (lines 691-698)
  - hex_edge_start_point for left/right (lines 657-662)
  - hex_edge_end_point for left/right (lines 753-759)

  Unexpected calls (fail loud):
  - hex_edge_endpoints (line 463)
  - adjacent in grid.m (lines 138, 168)

  Recommendation: Be consistent—either all should call unexpected/2 or the
  type system should prevent invalid combinations. A better approach: make
  wall_start_point and wall_end_point parametric on topology so the switch
  is complete.

  ---
  7. Encapsulating the hex boundary traversal order

  The relationship between edge traversal order and start/end points is
  implicit. The comments explain it, but it would be clearer to define:
  :- func edge_corners(direction) = {hex_corner, hex_corner}.  % (start, 
  end)

  This would document that lower_left goes from lower_left corner to left
  corner.

  ---
  8. The options module conflates concerns

  The options.m module defines:
  1. Command-line parsing (parse_options/4)
  2. The algorithm type
  3. The topology type
  4. The options record

  The algorithm and topology types are used throughout the codebase and are
  not really "option" types—they're domain types.

  Recommendation: Consider moving topology to grid.m (where it's most used)
  and algorithm to generate.m. The options module would then only contain
  parsing logic and the options record.

  ---
  9. boundary.m segment construction is verbose

  The hex_boundary_walls/1 function (lines 134-228) constructs 13 segments
  with repetitive patterns. This could be simplified with a helper that
  takes a cell generator and direction pair:

  :- func edge_sequence(list(cell), list(direction)) = list(boundary_wall).

  ---
  10. The check.m path-building is inefficient

  In dfs_check/8, the solution path is built using list append:
  PathToHere ++ [Neighbour]

  This is O(n) per step, making the whole solution O(n²). Since this runs on
   every maze, it could matter for large mazes.

  Recommendation: Build the path in reverse and reverse at the end, or use a
   difference list.

  ---
  Summary of Recommended Refactorings

  | Priority | Change                                                   |
  |----------|----------------------------------------------------------|
  | High     | Extract choose_random/4 to shared module                 |
  | High     | Consolidate neighbour-filtering predicates in maze.m     |
  | Medium   | Extract shuffle to shared module                         |
  | Medium   | Define hex corners once and derive edge endpoints        |
  | Low      | Remove unused wall_corner_point                          |
  | Low      | Move topology to grid.m, algorithm to generate.m         |
  | Low      | Consistent error handling for invalid topology/direction |
  | Low      | Fix O(n²) path-building in check.m                       |

  Would you like me to implement any of these changes?

> Please move choose_random to the generate module, as it will be visible to
 all submodules from there. Don't worry about extracting the shuffle. If the
 topology type is moved out of the options module then it would need to 
import it, which might cause other difficulties, so a good strategy is to 
define it in the `options` module and have every other module import that if
 they depend on the options. Leave error handling for the moment as we will 
deal with it later. Other than those things, please proceed as you 
suggested. 

● I'll implement these refactorings systematically.

● Update(generate.m)
  ⎿  Updated generate.m with 7 additions                                 
       23    :- include_module sidewinder.
       24    :- include_module wilson.
       25    
       26 +  :- import_module list.
       27    :- import_module maze.
       28    :- import_module options.
       29    :- import_module random.
     ...
       35    :- pred generate(algorithm::in, maze::in, maze::out,
       36        random.sfc16.random::in, random.sfc16.random::out) is 
            det.
       37    
       38 +      % Choose a random element from a non-empty list.
       39 +      % Throws an exception if the list is empty.
       40 +      %
       41 +  :- pred choose_random(list(T)::in, T::out,
       42 +      random.sfc16.random::in, random.sfc16.random::out) is 
          + det.
       43 +  
       44    %-----------------------------------------------------------
            ----------------%
       45    %-----------------------------------------------------------
            ----------------%
       46    

● Update(generate.m)
  ⎿  Updated generate.m with 3 additions                                 
       56    :- import_module generate.sidewinder.
       57    :- import_module generate.wilson.
       58    
       59 +  :- import_module int.
       60 +  :- import_module require.
       61 +  
       62    %-----------------------------------------------------------
            ----------------%
       63    
       64    generate(Algorithm, !Maze, !RNG) :-

● Update(generate.m)
  ⎿  Updated generate.m with 13 additions                                
        89        ).
        90    
        91    %----------------------------------------------------------
             -----------------%
        92 +  
        93 +  choose_random(List, Chosen, !RNG) :-
        94 +      (
        95 +          List = [],
        96 +          unexpected($pred, "empty list")
        97 +      ;
        98 +          List = [_ | _],
        99 +          Length = list.length(List),
       100 +          random.uniform_int_in_range(0, Length, Index, 
           + !RNG),
       101 +          list.det_index0(List, Index, Chosen)
       102 +      ).
       103 +  
       104 +  %----------------------------------------------------------
           + -----------------%
       105    :- end_module generate.
       106    %----------------------------------------------------------
             -----------------%

● Now let me add the neighbour-filtering predicates to maze.m:

● Update(maze.m)
  ⎿  Updated maze.m with 1 addition                                      
       17    :- import_module grid.
       18    :- import_module list.
       19    :- import_module options.
       20 +  :- import_module set_tree234.
       21    
       22    %-----------------------------------------------------------
            ----------------%
       23    

● Update(maze.m)
  ⎿  Updated maze.m with 14 additions                                    
        97        %
        98    :- func neighbours(maze, cell) = list(cell).
        99    
       100 +      % List all adjacent cells that are within the maze 
           + bounds.
       101 +      %
       102 +  :- func valid_neighbours(maze, cell) = list(cell).
       103 +  
       104 +      % List adjacent cells that are within the maze bounds 
           + and not in the
       105 +      % given set.
       106 +      %
       107 +  :- func unvisited_neighbours(maze, set_tree234(cell), cell)
           +  = list(cell).
       108 +  
       109 +      % List adjacent cells that are within the maze bounds 
           + and in the
       110 +      % given set.
       111 +      %
       112 +  :- func visited_neighbours(maze, set_tree234(cell), cell) =
           +  list(cell).
       113 +  
       114    %----------------------------------------------------------
             -----------------%
       115    %----------------------------------------------------------
             -----------------%
       116    

● Now I need to remove the duplicate import of set_tree234 in the
  implementation section:

● Update(maze.m)
  ⎿  Updated maze.m with 1 removal                                       
       117    :- implementation.
       118    
       119    :- import_module int.
       120 -  :- import_module set_tree234.
       120    :- import_module solutions.
       121    
       122    %----------------------------------------------------------
             -----------------%

● Now let me add the implementations of the new predicates at the end of the
   file:

● Read(maze.m)
  ⎿  Read 27 lines

● Update(maze.m)
  ⎿  Updated maze.m with 37 additions                                    
       271            Neighbours).
       272    
       273    %----------------------------------------------------------
             -----------------%
       274 +  
       275 +  valid_neighbours(Maze, Cell) = Neighbours :-
       276 +      Topology = Maze ^ m_topology,
       277 +      Dirs = directions(Topology),
       278 +      list.filter_map(
       279 +          ( pred(Dir::in, Neighbour::out) is semidet :-
       280 +              Neighbour = adjacent(Topology, Cell, Dir),
       281 +              in_maze(Maze, Neighbour)
       282 +          ),
       283 +          Dirs,
       284 +          Neighbours).
       285 +  
       286 +  unvisited_neighbours(Maze, Visited, Cell) = Unvisited :-
       287 +      Topology = Maze ^ m_topology,
       288 +      Dirs = directions(Topology),
       289 +      list.filter_map(
       290 +          ( pred(Dir::in, Neighbour::out) is semidet :-
       291 +              Neighbour = adjacent(Topology, Cell, Dir),
       292 +              in_maze(Maze, Neighbour),
       293 +              not set_tree234.member(Neighbour, Visited)
       294 +          ),
       295 +          Dirs,
       296 +          Unvisited).
       297 +  
       298 +  visited_neighbours(Maze, Visited, Cell) = VisitedNbrs :-
       299 +      Topology = Maze ^ m_topology,
       300 +      Dirs = directions(Topology),
       301 +      list.filter_map(
       302 +          ( pred(Dir::in, Neighbour::out) is semidet :-
       303 +              Neighbour = adjacent(Topology, Cell, Dir),
       304 +              in_maze(Maze, Neighbour),
       305 +              set_tree234.member(Neighbour, Visited)
       306 +          ),
       307 +          Dirs,
       308 +          VisitedNbrs).
       309 +  
       310 +  %----------------------------------------------------------
           + -----------------%
       311    :- end_module maze.
       312    %----------------------------------------------------------
             -----------------%

● Now let me work on the hex corners in render.m. First, I'll define the hex
   corner type and offset calculation:

● Update(render.m)
  ⎿  Updated render.m with 96 additions                                  
        84    :- func sqrt3 = float.
        85    sqrt3 = math.sqrt(3.0).
        86    
        87 +  %----------------------------------------------------------
           + -----------------%
        88 +  %
        89 +  % Hex corner geometry.
        90 +  %
        91 +  % A flat-topped hexagon has 6 corners, named by their 
           + position relative
        92 +  % to the centre. Going counter-clockwise from the right:
        93 +  %
        94 +  %              upper_left ----- upper_right
        95 +  %                       /         \
        96 +  %                      /           \
        97 +  %                 left               right
        98 +  %                      \           /
        99 +  %                       \         /
       100 +  %              lower_left ----- lower_right
       101 +  %
       102 +  
       103 +  :- type hex_corner
       104 +      --->    right
       105 +      ;       upper_right
       106 +      ;       upper_left
       107 +      ;       left
       108 +      ;       lower_left
       109 +      ;       lower_right.
       110 +  
       111 +      % Return the offset of a hex corner from the cell 
           + centre.
       112 +      % Sf is the cell spacing (distance from centre to 
           + left/right corners).
       113 +      %
       114 +  :- pred hex_corner_offset(float::in, hex_corner::in,
       115 +      float::out, float::out) is det.
       116 +  
       117 +  hex_corner_offset(Sf, Corner, DX, DY) :-
       118 +      (
       119 +          Corner = right,
       120 +          DX = Sf,
       121 +          DY = 0.0
       122 +      ;
       123 +          Corner = upper_right,
       124 +          DX = Sf / 2.0,
       125 +          DY = -Sf * sqrt3 / 2.0
       126 +      ;
       127 +          Corner = upper_left,
       128 +          DX = -Sf / 2.0,
       129 +          DY = -Sf * sqrt3 / 2.0
       130 +      ;
       131 +          Corner = left,
       132 +          DX = -Sf,
       133 +          DY = 0.0
       134 +      ;
       135 +          Corner = lower_left,
       136 +          DX = -Sf / 2.0,
       137 +          DY = Sf * sqrt3 / 2.0
       138 +      ;
       139 +          Corner = lower_right,
       140 +          DX = Sf / 2.0,
       141 +          DY = Sf * sqrt3 / 2.0
       142 +      ).
       143 +  
       144 +      % Return the two corners that bound an edge in the 
           + given direction.
       145 +      % The corners are ordered for counter-clockwise 
           + traversal around the cell
       146 +      % (which corresponds to clockwise traversal around the 
           + maze boundary).
       147 +      %
       148 +  :- pred hex_edge_corners(direction::in, hex_corner::out, 
           + hex_corner::out)
       149 +      is det.
       150 +  
       151 +  hex_edge_corners(Dir, StartCorner, EndCorner) :-
       152 +      (
       153 +          Dir = up,
       154 +          StartCorner = upper_left,
       155 +          EndCorner = upper_right
       156 +      ;
       157 +          Dir = upper_right,
       158 +          StartCorner = upper_right,
       159 +          EndCorner = right
       160 +      ;
       161 +          Dir = lower_right,
       162 +          StartCorner = right,
       163 +          EndCorner = lower_right
       164 +      ;
       165 +          Dir = down,
       166 +          StartCorner = lower_right,
       167 +          EndCorner = lower_left
       168 +      ;
       169 +          Dir = lower_left,
       170 +          StartCorner = lower_left,
       171 +          EndCorner = left
       172 +      ;
       173 +          Dir = upper_left,
       174 +          StartCorner = left,
       175 +          EndCorner = upper_left
       176 +      ;
       177 +          % Square directions - not valid for hex, but we 
           + need complete coverage
       178 +          ( Dir = left ; Dir = right ),
       179 +          StartCorner = right,
       180 +          EndCorner = right
       181 +      ).
       182 +  
       183        % Calculate viewbox dimensions based on topology.
       184        %
       185    :- pred viewbox_dimensions(topology::in, bounds::in, 
             int::in, int::in,

● Now let's update hex_edge_endpoints to use the new corner functions:

● Read(render.m)
  ⎿  Read 100 lines

● I notice the hex_edge_endpoints has different corner orderings than what
  hex_edge_corners specifies. Let me check what ordering makes sense.
  Looking at the existing code:
  - up: upper-left to upper-right (matches hex_edge_corners if we swap)
  - upper_right: upper-right to right (matches hex_edge_corners if we swap)

  It seems hex_edge_endpoints uses a different corner ordering (the ends are
   swapped from what hex_edge_corners would give for boundary traversal).
  Let me re-read the original hex_edge_endpoints to understand its usage.

  The internal wall edges just need both endpoints, order doesn't matter. So
   we can simplify:

● Update(render.m)
  ⎿  Updated render.m with 8 additions and 48 removals                   
       505    
       506        % Calculate hex edge endpoints for a given direction.
       507        % The direction is from the cell centre outward.
       508 +      % Uses hex_edge_corners to determine which corners 
           + bound the edge.
       509        %
       510    :- pred hex_edge_endpoints(float::in, float::in, float::in,
              direction::in,
       511        float::out, float::out, float::out, float::out) is det.
       512    
       513    hex_edge_endpoints(Sf, CX, CY, Dir, PX1, PY1, PX2, PY2) :-
       514 -      (
       515 -          Dir = up,
       516 -          % up edge: upper-left to upper-right corner
       517 -          PX1 = CX - Sf / 2.0,
       518 -          PY1 = CY - Sf * sqrt3 / 2.0,
       519 -          PX2 = CX + Sf / 2.0,
       520 -          PY2 = CY - Sf * sqrt3 / 2.0
       521 -      ;
       522 -          Dir = down,
       523 -          % down edge: lower-right to lower-left corner
       524 -          PX1 = CX + Sf / 2.0,
       525 -          PY1 = CY + Sf * sqrt3 / 2.0,
       526 -          PX2 = CX - Sf / 2.0,
       527 -          PY2 = CY + Sf * sqrt3 / 2.0
       528 -      ;
       529 -          Dir = upper_right,
       530 -          % upper_right edge: upper-right to right corner
       531 -          PX1 = CX + Sf / 2.0,
       532 -          PY1 = CY - Sf * sqrt3 / 2.0,
       533 -          PX2 = CX + Sf,
       534 -          PY2 = CY
       535 -      ;
       536 -          Dir = lower_left,
       537 -          % lower_left edge: left to lower-left corner
       538 -          PX1 = CX - Sf,
       539 -          PY1 = CY,
       540 -          PX2 = CX - Sf / 2.0,
       541 -          PY2 = CY + Sf * sqrt3 / 2.0
       542 -      ;
       543 -          Dir = upper_left,
       544 -          % upper_left edge: left to upper-left corner
       545 -          PX1 = CX - Sf,
       546 -          PY1 = CY,
       547 -          PX2 = CX - Sf / 2.0,
       548 -          PY2 = CY - Sf * sqrt3 / 2.0
       549 -      ;
       550 -          Dir = lower_right,
       551 -          % lower_right edge: right to lower-right corner
       552 -          PX1 = CX + Sf,
       553 -          PY1 = CY,
       554 -          PX2 = CX + Sf / 2.0,
       555 -          PY2 = CY + Sf * sqrt3 / 2.0
       556 -      ;
       557 -          ( Dir = left
       558 -          ; Dir = right
       559 -          ),
       560 -          unexpected($pred, "square direction used with hex 
           - topology")
       561 -      ).
       514 +      hex_edge_corners(Dir, Corner1, Corner2),
       515 +      hex_corner_offset(Sf, Corner1, DX1, DY1),
       516 +      hex_corner_offset(Sf, Corner2, DX2, DY2),
       517 +      PX1 = CX + DX1,
       518 +      PY1 = CY + DY1,
       519 +      PX2 = CX + DX2,
       520 +      PY2 = CY + DY2.
       521    
       522    :- func format_coord(float) = string.
       523    

● Now let me update hex_edge_start_point and hex_edge_end_point to use the
  corner functions:

● Read(render.m)
  ⎿  Read 150 lines

● I see that hex_edge_start_point and hex_edge_end_point use a different
  corner ordering than hex_edge_corners. Looking at the comments in
  hex_edge_start_point, the boundary traversal goes counter-clockwise around
   each cell. Let me check what hex_edge_corners defines:

  Looking at my hex_edge_corners:
  - lower_left: StartCorner = lower_left, EndCorner = left

  And hex_edge_start_point:
  - lower_left: start at lower-left corner (matches!)

  So hex_edge_corners already has the correct ordering for boundary
  traversal. Let me simplify these functions:

● Update(render.m)
  ⎿  Updated render.m with 5 additions and 62 removals                   
       649    
       650        % Get the starting point of a hex edge when tracing 
             clockwise around the maze.
       651        % This is counter-clockwise around the cell itself.
       652 +      % Uses hex_edge_corners to determine the start corner.
       653        %
       654    :- pred hex_edge_start_point(float::in, float::in, 
             float::in, direction::in,
       655        float::out, float::out) is det.
       656    
       657    hex_edge_start_point(Sf, CX, CY, Dir, PX, PY) :-
       658 -      % When tracing clockwise around the maze, we traverse 
           - each cell's boundary
       659 -      % edges counter-clockwise. The start point is where we 
           - enter the edge.
       660 -      %
       661 -      % Hex corners (relative to centre, with right = 0 
           - degrees):
       662 -      %   right:       (+S, 0)
       663 -      %   upper-right: (+S/2, -S*sqrt3/2)
       664 -      %   upper-left:  (-S/2, -S*sqrt3/2)
       665 -      %   left:        (-S, 0)
       666 -      %   lower-left:  (-S/2, +S*sqrt3/2)
       667 -      %   lower-right: (+S/2, +S*sqrt3/2)
       668 -      %
       669 -      % Edge traversal (counter-clockwise around cell = 
           - clockwise around maze):
       670 -      %   down:        lower-left → lower-right
       671 -      %   lower_right: lower-right → right
       672 -      %   upper_right: right → upper-right
       673 -      %   up:          upper-right → upper-left
       674 -      %   upper_left:  upper-left → left  [wait, should be: 
           - left → upper-left]
       675 -      %   lower_left:  left → lower-left  [wait, should be: 
           - lower-left → left]
       676 -      %
       677 -      % Actually, going counter-clockwise around the cell:
       678 -      %   From lower-left corner, the edges in order are:
       679 -      %   lower_left (lower-left → left), upper_left (left → 
           - upper-left),
       680 -      %   up (upper-left → upper-right), upper_right 
           - (upper-right → right),
       681 -      %   lower_right (right → lower-right), down 
           - (lower-right → lower-left)
       682 -      %
       683 -      (
       684 -          Dir = lower_left,
       685 -          % lower_left edge: lower-left corner → left corner
       686 -          PX = CX - Sf / 2.0,
       687 -          PY = CY + Sf * sqrt3 / 2.0
       688 -      ;
       689 -          Dir = upper_left,
       690 -          % upper_left edge: left corner → upper-left corner
       691 -          PX = CX - Sf,
       692 -          PY = CY
       693 -      ;
       694 -          Dir = up,
       695 -          % up edge: upper-left corner → upper-right corner
       696 -          PX = CX - Sf / 2.0,
       697 -          PY = CY - Sf * sqrt3 / 2.0
       698 -      ;
       699 -          Dir = upper_right,
       700 -          % upper_right edge: upper-right corner → right 
           - corner
       701 -          PX = CX + Sf / 2.0,
       702 -          PY = CY - Sf * sqrt3 / 2.0
       703 -      ;
       704 -          Dir = lower_right,
       705 -          % lower_right edge: right corner → lower-right 
           - corner
       706 -          PX = CX + Sf,
       707 -          PY = CY
       708 -      ;
       709 -          Dir = down,
       710 -          % down edge: lower-right corner → lower-left corner
       711 -          PX = CX + Sf / 2.0,
       712 -          PY = CY + Sf * sqrt3 / 2.0
       713 -      ;
       714 -          ( Dir = left
       715 -          ; Dir = right
       716 -          ),
       717 -          PX = 0.0,
       718 -          PY = 0.0
       719 -      ).
       658 +      hex_edge_corners(Dir, StartCorner, _EndCorner),
       659 +      hex_corner_offset(Sf, StartCorner, DX, DY),
       660 +      PX = CX + DX,
       661 +      PY = CY + DY.
       662    
       663        % Get the end point of a wall (clockwise direction).
       664        % This is the point we reach last when tracing the 
             boundary clockwise.

● Now let me update hex_edge_end_point:

● Read(render.m)
  ⎿  Read 80 lines

● Update(render.m)
  ⎿  Updated render.m with 5 additions and 44 removals                   
       707    
       708        % Get the ending point of a hex edge when tracing 
             clockwise around the maze.
       709        % This is counter-clockwise around the cell itself.
       710 +      % Uses hex_edge_corners to determine the end corner.
       711        %
       712    :- pred hex_edge_end_point(float::in, float::in, float::in,
              direction::in,
       713        float::out, float::out) is det.
       714    
       715    hex_edge_end_point(Sf, CX, CY, Dir, PX, PY) :-
       716 -      % End points matching the start points 
           - (counter-clockwise around cell):
       717 -      %   lower_left: lower-left → left (end = left)
       718 -      %   upper_left: left → upper-left (end = upper-left)
       719 -      %   up: upper-left → upper-right (end = upper-right)
       720 -      %   upper_right: upper-right → right (end = right)
       721 -      %   lower_right: right → lower-right (end = 
           - lower-right)
       722 -      %   down: lower-right → lower-left (end = lower-left)
       723 -      (
       724 -          Dir = lower_left,
       725 -          % lower_left edge: end at left corner
       726 -          PX = CX - Sf,
       727 -          PY = CY
       728 -      ;
       729 -          Dir = upper_left,
       730 -          % upper_left edge: end at upper-left corner
       731 -          PX = CX - Sf / 2.0,
       732 -          PY = CY - Sf * sqrt3 / 2.0
       733 -      ;
       734 -          Dir = up,
       735 -          % up edge: end at upper-right corner
       736 -          PX = CX + Sf / 2.0,
       737 -          PY = CY - Sf * sqrt3 / 2.0
       738 -      ;
       739 -          Dir = upper_right,
       740 -          % upper_right edge: end at right corner
       741 -          PX = CX + Sf,
       742 -          PY = CY
       743 -      ;
       744 -          Dir = lower_right,
       745 -          % lower_right edge: end at lower-right corner
       746 -          PX = CX + Sf / 2.0,
       747 -          PY = CY + Sf * sqrt3 / 2.0
       748 -      ;
       749 -          Dir = down,
       750 -          % down edge: end at lower-left corner
       751 -          PX = CX - Sf / 2.0,
       752 -          PY = CY + Sf * sqrt3 / 2.0
       753 -      ;
       754 -          ( Dir = left
       755 -          ; Dir = right
       756 -          ),
       757 -          PX = 0.0,
       758 -          PY = 0.0
       759 -      ).
       716 +      hex_edge_corners(Dir, _StartCorner, EndCorner),
       717 +      hex_corner_offset(Sf, EndCorner, DX, DY),
       718 +      PX = CX + DX,
       719 +      PY = CY + DY.
       720    
       721    %----------------------------------------------------------
             -----------------%
       722    

● Now let me also update render_hex_background_polygon to use the corner
  functions. First let me find it:

● Read(render.m)
  ⎿  Read 90 lines

● Let me update render_hex_background_polygon to use the corner functions.
  However, looking at this more carefully, the 12 o'clock and 6 o'clock
  points are not simple corner offsets - they're at the top of an upper
  corner and bottom of a lower corner (the topmost and bottommost points of
  the hex). Let me be more careful here.

  Looking at the code:
  - P10 (10 o'clock): left corner of cell (0, 0) → left corner
  - P12 (12 o'clock): top point → upper_right corner (the point at top,
  which has min Y)
  - P2 (2 o'clock): right corner of cell (W-1, HalfW) → right corner
  - P4 (4 o'clock): right corner of cell (W-1, HalfW+H-1) → right corner
  - P6 (6 o'clock): bottom point → lower_right corner (the point at bottom,
  which has max Y)
  - P8 (8 o'clock): left corner of cell (0, H-1) → left corner

  Wait, looking more carefully at P12: C12Y - Sf * sqrt3 / 2.0 is the Y of
  the upper_left or upper_right corners (they have the same Y). The X is
  just the cell centre X. So P12 is not exactly a corner, but is equivalent
  to the upper corner Y with the cell centre X.

  Actually, looking at hex_corner_offset for upper_right: DY = -Sf * sqrt3 /
   2.0, which matches. And for a regular pointy-topped hexagon shape, at 12
  o'clock the polygon vertex is between the upper_left and upper_right
  corners of the topmost cell - it's at the cell centre X with the upper
  corner Y.

  This is not a corner offset - it's a special case. Let me just use corner
  offsets where applicable:

● Update(render.m)
  ⎿  Updated render.m with 27 additions and 22 removals                  
       338    
       339        % The six corner cells and their outermost hex corners:
       340        % 10 o'clock (0, 0): left corner
       341 -      % 12 o'clock (HalfW, 0): upper-left and upper-right
           -   corners
       342 -      % 2 o'clock (W-1, HalfW): upper-right corner
       343 -      % 4 o'clock (W-1, HalfW + H - 1): right 
           -  and lower-right corners
       344 -      % 6 o'clock (HalfW, HalfW + H - 1): lower-right
           -   and lower-left corners
       345 -      % 8 o'clock (0, H - 1): lower-left corner
       341 +      % 12 o'clock (HalfW, 0): top point (between 
           +  upper-left and upper-right)
       342 +      % 2 o'clock (W-1, HalfW): right corner
       343 +      % 4 o'clock (W-1, HalfW + H - 1): right corner
       344 +      % 6 o'clock (HalfW, HalfW + H - 1): 
           +  bottom point (between lower-left and lower-right)
       345 +      % 8 o'clock (0, H - 1): left corner
       346    
       347 -      % Get the boundary polygon vertices
       348 -      % We trace clockwise around the outside of the hex maze
       347 +      % Get the cell centres for each corner of the maze
       348        hex_cell_centre(S, M, Bounds, cell(0, 0), C10X, C10Y),
       349        hex_cell_centre(S, M, Bounds, cell(HalfW, 0), C12X, 
             C12Y),
       350        hex_cell_centre(S, M, Bounds, cell(W - 1, HalfW), C2X, 
             C2Y),
     ...
       353        hex_cell_centre(S, M, Bounds, cell(HalfW, HalfW + H - 
             1), C6X, C6Y),
       354        hex_cell_centre(S, M, Bounds, cell(0, H - 1), C8X, 
             C8Y),
       355    
       356 -      % Calculate the 6 polygon vertices (outermost points)
       356 +      % Calculate the 6 polygon vertices using 
           +  corner offsets where applicable
       357        % 10 o'clock: left corner of cell (0, 0)
       358 -      P10X = C10X - Sf,
       359 -      P10Y = C10Y,
       360 -      % 12 o'clock: top point between cells
       358 +      hex_corner_offset(Sf, left, D10X, D10Y),
       359 +      P10X = C10X + D10X,
       360 +      P10Y = C10Y + D10Y,
       361 +      % 12 o'clock: top point (at upper corner Y, cell centre
           +  X)
       362 +      hex_corner_offset(Sf, upper_right, _, D12Y),
       363        P12X = C12X,
       364 -      P12Y = C12Y - Sf * sqrt3 / 2.0,
       365 -      % 2 o'clock: upper-right corner of cell (W-1, HalfW)
       366 -      P2X = C2X + Sf,
       367 -      P2Y = C2Y,
       364 +      P12Y = C12Y + D12Y,
       365 +      % 2 o'clock: right corner of cell (W-1, HalfW)
       366 +      hex_corner_offset(Sf, right, D2X, D2Y),
       367 +      P2X = C2X + D2X,
       368 +      P2Y = C2Y + D2Y,
       369        % 4 o'clock: right corner of cell (W-1, HalfW + H - 1)
       370 -      P4X = C4X + Sf,
       371 -      P4Y = C4Y,
       372 -      % 6 o'clock: bottom point between cells
       370 +      hex_corner_offset(Sf, right, D4X, D4Y),
       371 +      P4X = C4X + D4X,
       372 +      P4Y = C4Y + D4Y,
       373 +      % 6 o'clock: bottom point (at lower corner Y, cell 
           + centre X)
       374 +      hex_corner_offset(Sf, lower_right, _, D6Y),
       375        P6X = C6X,
       376 -      P6Y = C6Y + Sf * sqrt3 / 2.0,
       377 -      % 8 o'clock: lower-left corner of cell (0, H - 1)
       378 -      P8X = C8X - Sf,
       379 -      P8Y = C8Y,
       376 +      P6Y = C6Y + D6Y,
       377 +      % 8 o'clock: left corner of cell (0, H - 1)
       378 +      hex_corner_offset(Sf, left, D8X, D8Y),
       379 +      P8X = C8X + D8X,
       380 +      P8Y = C8Y + D8Y,
       381    
       382        % Format the polygon points
       383        PointsStr = string.format("%s,%s %s,%s %s,%s %s,%s 
             %s,%s %s,%s",

● Now let me remove the unused wall_corner_point function:

● Search(pattern: "wall_corner_point", path: "~/Documents/projects/amaze",
        output_mode: "content")
  ⎿  Found 27 lines (ctrl+o to expand)

● The function is only defined in render.m and only used in transcripts
  (historical). Let me confirm it's not used in the actual code:

● Search(pattern: "wall_corner_point", path: "~/Documents/projects/amaze", glob:
         "*.m", output_mode: "content")
  ⎿  Found 2 lines (ctrl+o to expand)

● Good, it's only defined and not used elsewhere. Let me remove it:

● Read(render.m)
  ⎿  Read 20 lines

● Update(render.m)
  ⎿  Updated render.m with 8 removals                                   
       597            [s(PointsStr), s(RenderOpts ^ 
             ro_boundary_wall_color),
       598             i(RenderOpts ^ ro_boundary_wall_width)], !IO).
       599    
       600 -      % Get the corner point for a boundary wall.
       601 -      % This is the corner at the "start" of the wall when 
           - tracing clockwise.
       602 -      %
       603 -  :- func wall_corner_point(topology, bounds, int, int, 
           - boundary_wall) = string.
       604 -  
       605 -  wall_corner_point(Topology, Bounds, S, M, Wall) =
       606 -      wall_start_point(Topology, Bounds, S, M, Wall).
       607 -  
       600        % Get the start point of a wall (clockwise direction).
       601        % This is the point we reach first when tracing the 
             boundary clockwise.
       602        %

● Now let me fix the O(n²) path-building in check.m:

● Read(check.m)
  ⎿  Read 125 lines

● The problem is on line 114: PathToHere ++ [Neighbour] which is O(n) for
  each step. I'll change it to build the path in reverse (prepend which is
  O(1)), and reverse at the end:

● Update(check.m)
  ⎿  Updated check.m with 12 additions and 10 removals                   
       48        StartCell = get_start_cell(Maze),
       49        TargetCell = get_target_cell(Maze),
       50        Visited0 = set_tree234.init,
       51 -      PathToHere = [StartCell],
       52 -      dfs_check(Maze, TargetCell, StartCell, PathToHere, 
          - Visited0, Visited,
       53 -          no, MaybeSolution),
       51 +      % Build path in reverse for O(1) prepend, reverse at end
       52 +      RevPathToHere = [StartCell],
       53 +      dfs_check(Maze, TargetCell, StartCell, RevPathToHere, 
          + Visited0, Visited,
       54 +          no, MaybeRevSolution),
       55    
       56        % Check that all cells were visited
       57        AllCells = cells(Maze),
     ...
       66    
       67        % Check that we found a solution
       68        (
       69 -          MaybeSolution = yes(Solution)
       69 +          MaybeRevSolution = yes(RevSolution),
       70 +          Solution = list.reverse(RevSolution)
       71        ;
       72 -          MaybeSolution = no,
       72 +          MaybeRevSolution = no,
       73            throw("no solution found" : string)
       74        ).
       75    
       76        % DFS traversal to check the maze and find the solution.
       77        %
       78 -      % PathToHere
          -   is the path from start to Current (inclusive), in order.
       79 -      % We pass it to record the solution when we reach the 
          - target.
       78 +      % RevPathToHere
          +   is the path from start to Current (inclusive), in reverse.
       79 +      % We build it in reverse for O(1) prepend, then reverse 
          + at the end.
       80        %
       81    :- pred dfs_check(maze::in, cell::in, cell::in, 
            list(cell)::in,
       82        set_tree234(cell)::in, set_tree234(cell)::out,
       83        maybe(list(cell))::in, maybe(list(cell))::out) is det.
       84    
       85 -  dfs_check(Maze, TargetCell, Current, PathToHere
          -  , !Visited, !MaybeSolution) :-
       85 +  dfs_check(Maze, TargetCell, Current, RevPathToHere
          +  , !Visited, !MaybeSolution) :-
       86        Current = cell(X, Y),
       87    
       88        % Check for loop (cell already visited)
     ...
        97    
        98        % Check if we reached the target
        99        ( if Current = TargetCell then
       100 -          !:MaybeSolution = yes(PathToHere)
       100 +          !:MaybeSolution = yes(RevPathToHere)
       101        else
       102            true
       103        ),
     ...
       111                    V = V0,
       112                    S = S0
       113                else
       114 -                  dfs_check(Maze, TargetCell, Neighbour, 
           -  PathToHere ++ [Neighbour],
       114 +                  dfs_check(Maze, TargetCell, Neighbour, 
           +  [Neighbour | RevPathToHere],
       115                        V0, V, S0, S)
       116                )
       117            ),

● Now let me update all the generate submodules to use the shared
  predicates. I'll start with generate.dfs.m:

● Update(generate.dfs.m)
  ⎿  Updated generate.dfs.m with 1 addition and 2 removals               
       30    
       31    :- implementation.
       32    
       33 +  :- import_module generate.
       34    :- import_module grid.
       35    :- import_module options.
       36    
       37 -  :- import_module int.
       37    :- import_module list.
       38 -  :- import_module require.
       38    :- import_module set_tree234.
       39    
       40    %-----------------------------------------------------------
            ----------------%

● Now remove the local unvisited_neighbours and choose_random from
  generate.dfs.m:

● Update(generate.dfs.m)
  ⎿  Updated generate.dfs.m with 32 removals                             
        82            )
        83        ).
        84    
        85 -      % Get neighbours of a cell that are within the maze and
           -  not yet visited.
        86 -      %
        87 -  :- func unvisited_neighbours(maze, set_tree234(cell), cell)
           -  = list(cell).
        88 -  
        89 -  unvisited_neighbours(Maze, Visited, Cell) = Unvisited :-
        90 -      Topology = get_topology(Maze),
        91 -      Dirs = directions(Topology),
        92 -      list.filter_map(
        93 -          ( pred(Dir::in, Neighbour::out) is semidet :-
        94 -              Neighbour = adjacent(Topology, Cell, Dir),
        95 -              in_maze(Maze, Neighbour),
        96 -              not set_tree234.member(Neighbour, Visited)
        97 -          ),
        98 -          Dirs,
        99 -          Unvisited).
       100 -  
       101 -      % Choose a random element from a non-empty list.
       102 -      %
       103 -  :- pred choose_random(list(T)::in, T::out,
       104 -      random.sfc16.random::in, random.sfc16.random::out) is 
           - det.
       105 -  
       106 -  choose_random(List, Chosen, !RNG) :-
       107 -      (
       108 -          List = [],
       109 -          unexpected($pred, "empty list")
       110 -      ;
       111 -          List = [_ | _],
       112 -          Length = list.length(List),
       113 -          random.uniform_int_in_range(0, Length, Index, 
           - !RNG),
       114 -          list.det_index0(List, Index, Chosen)
       115 -      ).
       116 -  
        85    %----------------------------------------------------------
             -----------------%
        86    :- end_module generate.dfs.
        87    %----------------------------------------------------------
             -----------------%

● Now let me update generate.prim.m:

● Update(generate.prim.m)
  ⎿  Updated generate.prim.m with 1 addition and 1 removal               
       41    
       42    :- implementation.
       43    
       44 +  :- import_module generate.
       45    :- import_module grid.
       46    :- import_module options.
       47    
       48    :- import_module list.
       49 -  :- import_module require.
       49    :- import_module set_tree234.
       50    
       51    %-----------------------------------------------------------
            ----------------%

● Now remove the local valid_neighbours and choose_random from
  generate.prim.m:

● Update(generate.prim.m)
  ⎿  Updated generate.prim.m with 5 additions and 46 removals            
       83            set_tree234.delete(ChosenCell, !Frontier),
       84    
       85            % Find neighbours of chosen cell that are in the 
            maze
       86 -          AllNeighbours = valid_neighbours(!.Maze, 
          - ChosenCell),
       87 -          InMazeNeighbours = list.filter(
       88 -              ( pred(C::in) is semidet :- 
          - set_tree234.member(C, !.InMaze) ),
       89 -              AllNeighbours),
       86 +          InMazeNeighbours = visited_neighbours(!.Maze, 
          + !.InMaze, ChosenCell),
       87    
       88            % Pick one randomly and carve a door
       89 -          (
       90 -              InMazeNeighbours = [],
       91 -              % This shouldn't happen if frontier is 
          - maintained correctly
       92 -              unexpected($pred, "frontier cell has no in-maze 
          - neighbours")
       93 -          ;
       94 -              InMazeNeighbours = [_ | _],
       95 -              choose_random(InMazeNeighbours, ConnectTo, 
          - !RNG),
       96 -              Topology = get_topology(!.Maze),
       97 -              Edge = get_edge_between(Topology, ChosenCell, 
          - ConnectTo),
       98 -              !:Maze = add_door(!.Maze, Edge)
       99 -          ),
       89 +          choose_random(InMazeNeighbours, ConnectTo, !RNG),
       90 +          Topology = get_topology(!.Maze),
       91 +          Edge = get_edge_between(Topology, ChosenCell, 
          + ConnectTo),
       92 +          !:Maze = add_door(!.Maze, Edge),
       93    
       94            % Add chosen cell to the maze
       95            set_tree234.insert(ChosenCell, !InMaze),
     ...
       111            prim_loop(!InMaze, !Frontier, !Maze, !RNG)
       112        ).
       113    
       114 -      % Get all neighbours of a cell that are within the maze
           -  bounds.
       115 -      %
       116 -  :- func valid_neighbours(maze, cell) = list(cell).
       117 -  
       118 -  valid_neighbours(Maze, Cell) = Neighbours :-
       119 -      Topology = get_topology(Maze),
       120 -      Dirs = directions(Topology),
       121 -      list.filter_map(
       122 -          ( pred(Dir::in, Neighbour::out) is semidet :-
       123 -              Neighbour = adjacent(Topology, Cell, Dir),
       124 -              in_maze(Maze, Neighbour)
       125 -          ),
       126 -          Dirs,
       127 -          Neighbours).
       128 -  
       114        % Add unvisited neighbours of a cell to the frontier.
       115        %
       116    :- pred add_unvisited_to_frontier(maze::in, 
             set_tree234(cell)::in, cell::in,
     ...
       146            Neighbours,
       147            !Frontier).
       148    
       149 -      % Choose a random element from a non-empty list.
       150 -      %
       151 -  :- pred choose_random(list(T)::in, T::out,
       152 -      random.sfc16.random::in, random.sfc16.random::out) is 
           - det.
       153 -  
       154 -  choose_random(List, Chosen, !RNG) :-
       155 -      (
       156 -          List = [],
       157 -          unexpected($pred, "empty list")
       158 -      ;
       159 -          List = [_ | _],
       160 -          Length = list.length(List),
       161 -          random.uniform_int_in_range(0, Length, Index, 
           - !RNG),
       162 -          list.det_index0(List, Index, Chosen)
       163 -      ).
       164 -  
       149    %----------------------------------------------------------
             -----------------%
       150    :- end_module generate.prim.
       151    %----------------------------------------------------------
             -----------------%

● Now let me update generate.hunt_and_kill.m:

● Update(generate.hunt_and_kill.m)
  ⎿  Updated generate.hunt_and_kill.m with 1 addition and 2 removals     
       37    
       38    :- implementation.
       39    
       40 +  :- import_module generate.
       41    :- import_module grid.
       42    :- import_module options.
       43    
       44 -  :- import_module int.
       44    :- import_module list.
       45    :- import_module maybe.
       46 -  :- import_module require.
       46    :- import_module set_tree234.
       47    
       48    %-----------------------------------------------------------
            ----------------%

● Update(generate.hunt_and_kill.m)
  ⎿  Updated generate.hunt_and_kill.m with 3 additions and 51 removals   
       124            find_hunt_target_loop(Maze, Visited, Rest, 
             MaybeTarget)
       125        else
       126            % Cell is unvisited - check if it has any visited 
             neighbours
       127 -          VisitedNeighbours
           -   = visited_neighbours(Maze, Visited, Cell),
       127 +          VisitedNbrs
           +   = visited_neighbours(Maze, Visited, Cell),
       128            (
       129 -              VisitedNeighbours = [Neighbour | _],
       129 +              VisitedNbrs = [Neighbour | _],
       130                % Found a target
       131                MaybeTarget = yes({Cell, Neighbour})
       132            ;
       133 -              VisitedNeighbours = [],
       133 +              VisitedNbrs = [],
       134                % No visited neighbours, keep searching
       135                find_hunt_target_loop(Maze, Visited, Rest, 
             MaybeTarget)
       136            )
       137        ).
       138    
       139 -      % Get neighbours of a cell that are within the maze and
           -  not yet visited.
       140 -      %
       141 -  :- func unvisited_neighbours(maze, set_tree234(cell), cell)
           -  = list(cell).
       142 -  
       143 -  unvisited_neighbours(Maze, Visited, Cell) = Unvisited :-
       144 -      Topology = get_topology(Maze),
       145 -      Dirs = directions(Topology),
       146 -      list.filter_map(
       147 -          ( pred(Dir::in, Neighbour::out) is semidet :-
       148 -              Neighbour = adjacent(Topology, Cell, Dir),
       149 -              in_maze(Maze, Neighbour),
       150 -              not set_tree234.member(Neighbour, Visited)
       151 -          ),
       152 -          Dirs,
       153 -          Unvisited).
       154 -  
       155 -      % Get neighbours of a cell that are within the maze and
           -  already visited.
       156 -      %
       157 -  :- func visited_neighbours(maze, set_tree234(cell), cell) =
           -  list(cell).
       158 -  
       159 -  visited_neighbours(Maze, Visited, Cell) = VisitedNbrs :-
       160 -      Topology = get_topology(Maze),
       161 -      Dirs = directions(Topology),
       162 -      list.filter_map(
       163 -          ( pred(Dir::in, Neighbour::out) is semidet :-
       164 -              Neighbour = adjacent(Topology, Cell, Dir),
       165 -              in_maze(Maze, Neighbour),
       166 -              set_tree234.member(Neighbour, Visited)
       167 -          ),
       168 -          Dirs,
       169 -          VisitedNbrs).
       170 -  
       171 -      % Choose a random element from a non-empty list.
       172 -      %
       173 -  :- pred choose_random(list(T)::in, T::out,
       174 -      random.sfc16.random::in, random.sfc16.random::out) is 
           - det.
       175 -  
       176 -  choose_random(List, Chosen, !RNG) :-
       177 -      (
       178 -          List = [],
       179 -          unexpected($pred, "empty list")
       180 -      ;
       181 -          List = [_ | _],
       182 -          Length = list.length(List),
       183 -          random.uniform_int_in_range(0, Length, Index, 
           - !RNG),
       184 -          list.det_index0(List, Index, Chosen)
       185 -      ).
       186 -  
       139    %----------------------------------------------------------
             -----------------%
       140    :- end_module generate.hunt_and_kill.
       141    %----------------------------------------------------------
             -----------------%

● Now let me update generate.aldous_broder.m:

● Update(generate.aldous_broder.m)
  ⎿  Updated generate.aldous_broder.m with 1 addition and 1 removal      
       40    
       41    :- implementation.
       42    
       43 +  :- import_module generate.
       44    :- import_module grid.
       45    :- import_module options.
       46    
       47    :- import_module int.
       48    :- import_module list.
       49 -  :- import_module require.
       49    :- import_module set_tree234.
       50    
       51    %-----------------------------------------------------------
            ----------------%

● Update(generate.aldous_broder.m)
  ⎿  Updated generate.aldous_broder.m with 1 addition and 32 removals    
       79            true
       80        else
       81            % Choose a random neighbour (must be in maze)
       82 -          Neighbours = all_neighbours(!.Maze, Current),
       82 +          Neighbours = valid_neighbours(!.Maze, Current),
       83            choose_random(Neighbours, Next, !RNG),
       84            % Check if next cell is unvisited
       85            ( if set_tree234.member(Next, !.Visited) then
     ...
        95            )
        96        ).
        97    
        98 -      % Get all neighbours of a cell that are within the 
           - maze.
        99 -      %
       100 -  :- func all_neighbours(maze, cell) = list(cell).
       101 -  
       102 -  all_neighbours(Maze, Cell) = Neighbours :-
       103 -      Topology = get_topology(Maze),
       104 -      Dirs = directions(Topology),
       105 -      list.filter_map(
       106 -          ( pred(Dir::in, Neighbour::out) is semidet :-
       107 -              Neighbour = adjacent(Topology, Cell, Dir),
       108 -              in_maze(Maze, Neighbour)
       109 -          ),
       110 -          Dirs,
       111 -          Neighbours).
       112 -  
       113 -      % Choose a random element from a non-empty list.
       114 -      %
       115 -  :- pred choose_random(list(T)::in, T::out,
       116 -      random.sfc16.random::in, random.sfc16.random::out) is 
           - det.
       117 -  
       118 -  choose_random(List, Chosen, !RNG) :-
       119 -      (
       120 -          List = [],
       121 -          unexpected($pred, "empty list")
       122 -      ;
       123 -          List = [_ | _],
       124 -          Length = list.length(List),
       125 -          random.uniform_int_in_range(0, Length, Index, 
           - !RNG),
       126 -          list.det_index0(List, Index, Chosen)
       127 -      ).
       128 -  
        98    %----------------------------------------------------------
             -----------------%
        99    :- end_module generate.aldous_broder.
       100    %----------------------------------------------------------
             -----------------%

● Now let me update generate.wilson.m:

● Update(generate.wilson.m)
  ⎿  Updated generate.wilson.m with 1 addition and 2 removals            
       40    
       41    :- implementation.
       42    
       43 +  :- import_module generate.
       44    :- import_module grid.
       45    :- import_module options.
       46    
       47 -  :- import_module assoc_list.
       47    :- import_module int.
       48    :- import_module list.
       49    :- import_module map.
       50 -  :- import_module require.
       50    :- import_module set_tree234.
       51    
       52    %-----------------------------------------------------------
            ----------------%

● Update(generate.wilson.m)
  ⎿  Updated generate.wilson.m with 1 addition and 1 removal            
       117            true
       118        else
       119            % Choose a random neighbour
       120 -          Neighbours = all_neighbours(Maze, Current),
       120 +          Neighbours = valid_neighbours(Maze, Current),
       121            choose_random(Neighbours, Next, !RNG),
       122            % If we've visited Current before, this creates a 
             loop.
       123            % By updating the map, we effectively erase the 
             loop.

● Now remove the local all_neighbours and choose_random from the end of
  generate.wilson.m:

● Read(generate.wilson.m)
  ⎿  Read 45 lines

● Update(generate.wilson.m)
  ⎿  Updated generate.wilson.m with 31 removals                          
       172            )
       173        ).
       174    
       175 -      % Get all neighbours of a cell that are within the maze
           -  bounds.
       176 -      %
       177 -  :- func all_neighbours(maze, cell) = list(cell).
       178 -  
       179 -  all_neighbours(Maze, Cell) = Neighbours :-
       180 -      Topology = get_topology(Maze),
       181 -      Dirs = directions(Topology),
       182 -      list.filter_map(
       183 -          ( pred(Dir::in, Neighbour::out) is semidet :-
       184 -              Neighbour = adjacent(Topology, Cell, Dir),
       185 -              in_maze(Maze, Neighbour)
       186 -          ),
       187 -          Dirs,
       188 -          Neighbours).
       189 -  
       190 -      % Choose a random element from a non-empty list.
       191 -      %
       192 -  :- pred choose_random(list(T)::in, T::out,
       193 -      random.sfc16.random::in, random.sfc16.random::out) is 
           - det.
       194 -  
       195 -  choose_random(List, Chosen, !RNG) :-
       196 -      (
       197 -          List = [],
       198 -          unexpected($pred, "empty list")
       199 -      ;
       200 -          List = [_ | _],
       201 -          Length = list.length(List),
       202 -          random.uniform_int_in_range(0, Length, Index, 
           - !RNG),
       203 -          list.det_index0(List, Index, Chosen)
       204 -      ).
       205 -  
       175    %----------------------------------------------------------
             -----------------%
       176    :- end_module generate.wilson.
       177    %----------------------------------------------------------
             -----------------%

● I need to add require import back for unexpected:

● Update(generate.wilson.m)
  ⎿  Updated generate.wilson.m with 1 addition                           
       47    :- import_module int.
       48    :- import_module list.
       49    :- import_module map.
       50 +  :- import_module require.
       51    :- import_module set_tree234.
       52    
       53    %-----------------------------------------------------------
            ----------------%

● Now let me update generate.kruskal.m. This one has choose_random inline in
   the shuffle logic, but it uses its own shuffle, so I'll just import
  generate for choose_random if needed:

● Read(generate.kruskal.m)
  ⎿  Read 183 lines

● generate.kruskal.m doesn't use choose_random - it uses its own shuffle,
  which doesn't need choose_random. No changes needed for this file.

  Now let me update the todo list and build/test:

● Bash(mmc --make amaze 2>&1)
  ⎿  Making Mercury/int3s/amaze.int3   
     Making Mercury/int3s/boundary.int3
     Making Mercury/int3s/grid.int3
     … +87 lines (ctrl+o to expand)

● The build succeeded with only ambiguity warnings. Now let me test with
  various algorithms and topologies:

● Bash(for algo in dfs kruskal prim aldous-broder wilson hunt-and-kill; do echo
      "=== Testing $algo (square) ===" && ./amaze -a $algo -s 5 -r 42 -p
      /tmp/test_sq_$algo.s…)
  ⎿  === Testing dfs (square) ===    
     OK
     === Testing kruskal (square) ===
     … +9 lines (ctrl+o to expand)

● Bash(for algo in dfs kruskal prim aldous-broder wilson hunt-and-kill; do echo
      "=== Testing $algo (hex) ===" && ./amaze -t hex -a $algo -s 3 -r 42 -p
      /tmp/test_hex_$a…)
  ⎿  === Testing dfs (hex) ===    
     OK
     === Testing kruskal (hex) ===
     … +9 lines (ctrl+o to expand)

● Bash(for algo in binary-tree sidewinder; do echo "=== Testing $algo (square)
      ===" && ./amaze -a $algo -s 5 -r 42 -p /tmp/test_sq_$algo.svg && echo
      "OK"; done)
  ⎿  === Testing binary-tree (square) ===
     OK
     === Testing sidewinder (square) ===
     OK

● Let me visually verify one of each topology by looking at the SVG:

● Read(/tmp/test_sq_dfs.svg)
  ⎿  Read 24 lines

● Read(/tmp/test_hex_dfs.svg)
  ⎿  Read 32 lines

● Both look good! The SVGs have the expected structure. Let me update the
  todo list:

● All refactoring tasks are complete. Here's a summary of the changes:

  Summary of Refactoring Changes

  1. Consolidated choose_random/4 in generate.m

  - Added choose_random/4 to the generate.m interface (visible to all
  submodules)
  - Removed duplicate implementations from: generate.dfs.m, generate.prim.m,
   generate.hunt_and_kill.m, generate.aldous_broder.m, generate.wilson.m

  2. Added neighbour-filtering predicates to maze.m

  - Added valid_neighbours/2 - all neighbours within maze bounds
  - Added unvisited_neighbours/3 - neighbours not in a given set
  - Added visited_neighbours/3 - neighbours in a given set
  - Updated all generate submodules to use these instead of local
  implementations

  3. Defined hex corner geometry in render.m

  - Added hex_corner type with 6 positions
  - Added hex_corner_offset/4 - calculates X,Y offset from cell centre for
  any corner
  - Added hex_edge_corners/3 - returns the two corners bounding an edge
  - Simplified hex_edge_endpoints/8, hex_edge_start_point/6,
  hex_edge_end_point/6 to use these primitives
  - Updated render_hex_background_polygon/4 to use corner offsets

  4. Removed unused wall_corner_point from render.m

  - This was just forwarding to wall_start_point and was never called

  5. Fixed O(n²) path-building in check.m

  - Changed from PathToHere ++ [Neighbour] (O(n) per step) to [Neighbour | 
  RevPathToHere] (O(1))
  - Reverse the path once at the end

  Code reduction

  - Removed ~150 lines of duplicated code across the generate submodules
  - The hex rendering code is now more maintainable with centralized corner
  geometry

> /context 
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     SlashCommand Tool · 0 commands
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> /export transcript8.txt 
  ⎿  Conversation exported to: transcript8.txt

> Let's add a subsection for Iteration 7, the goal of which is to add final 
polish to the project. Our checklist should be as follows (the first two 
items are already complete):
- review codebase
- implement refactorings and cleanup
- graceful error handling
- write README.md 

● I'll add Iteration 7 to the PLAN.md file. Let me first read the current
  plan to see where to add it.

● Read(PLAN.md)
  ⎿  Read 1052 lines

● Now I'll add Iteration 7 at the end of the file:

● Update(PLAN.md)
  ⎿  Updated PLAN.md with 13 additions                                  
       1049    - [x] Add error handling for Binary Tree and Sidewinder 
              with hex topology
       1050    - [x] Add direction_delta to grid.m for consistent basis 
              handling
       1051    - [x] Update size option interpretation for hex (N means 
              W=2N-1, H=N)
       1052 +  
       1053 +  ### Iteration 7 (In Progress)
       1054 +  
       1055 +  **Goals:**
       1056 +  
       1057 +  Add final polish to the project.
       1058 +  
       1059 +  **Tasks:**
       1060 +  
       1061 +  - [x] Review codebase for clarity and modularity
       1062 +  - [x] Implement refactorings and cleanup
       1063 +  - [ ] Graceful error handling
       1064 +  - [ ] Write README.md

● Iteration 7 has been added to the plan with the first two items already
  checked off (the code review and refactoring we just completed). The
  remaining tasks are:

  1. Graceful error handling - Replace exceptions with proper error
  reporting to stderr
  2. Write README.md - Document how to build and use the program



