Refactor to be functional

1 files changed, 15 insertions, 16 deletions

diff --git a/docs/entities.org b/docs/entities.org
index 048cd8e..3766522 100644
--- a/docs/entities.org
+++ b/docs/entities.org
@@ -126,19 +126,19 @@ The engine recognizes these standard keys. Use them to integrate with the physic
 | ~#:anim-tick~ | integer | Tick counter for frame timing (0 to ~#:duration - 1~). Incremented by ~animate-entity~; resets when frame advances. |
 | ~#:group-id~ | symbol | Shared id for one rigid assembly (from ~instantiate-group-prefab~). All parts and the origin share the same symbol. |
 | ~#:group-origin?~ | boolean | When ~#t~, this entity is the assembly’s pose origin; world ~#:x~ / ~#:y~ drive the group. Members should not set this. |
-| ~#:group-local-x~, ~#:group-local-y~ | number | Offset from the origin’s top-left corner; members’ world position is origin + local (updated by ~scene-sync-groups!~). |
+| ~#:group-local-x~, ~#:group-local-y~ | number | Offset from the origin’s top-left corner; members’ world position is origin + local (updated by ~scene-sync-groups~). |
 | ~#:skip-render~ | boolean | When ~#t~, ~render-scene!~ skips drawing this entity (used for invisible origins). |
 
 * Entity groups (prefab assemblies)
 
 A **group prefab** describes one *origin* entity plus several *parts* with local offsets. Data lives in the optional ~group-prefabs~ section of the prefab file (alongside ~mixins~ and ~prefabs~). Each group entry has the shape ~(name #:type-members SYMBOL #:parts (part ...) ...)~ with two optional flags:
 
-- ~#:pose-only-origin?~ — when ~#t~ (typical for tweened platforms), the origin is invisible, does not run physics pipelines, and is driven by tweens or scripts. When ~#f~ (default), the origin uses a small *physics-driving* profile (~#:gravity? #t~, no ~#:skip-pipelines~): integrate the origin like a mover, then call ~scene-sync-groups!~ so parts stay glued as a rigid body. For that case, set ~#:origin-width~ and ~#:origin-height~ to the full assembly size (same box as the combined parts); otherwise the origin stays 0×0 and tile collision only sees a point at the reference corner, which can leave the raft overlapping solid floor tiles.
+- ~#:pose-only-origin?~ — when ~#t~ (typical for tweened platforms), the origin is invisible, does not run physics pipelines, and is driven by tweens or scripts. When ~#f~ (default), the origin uses a small *physics-driving* profile (~#:gravity? #t~, no ~#:skip-pipelines~): integrate the origin like a mover, then call ~scene-sync-groups~ so parts stay glued as a rigid body. For that case, set ~#:origin-width~ and ~#:origin-height~ to the full assembly size (same box as the combined parts); otherwise the origin stays 0×0 and tile collision only sees a point at the reference corner, which can leave the raft overlapping solid floor tiles.
 - ~#:static-parts?~ — when ~#t~, each part gets static rigid-body defaults (no gravity on parts; pose comes from the origin). When ~#f~ (default), parts only have what you put in each part plist.
 
 Each ~part~ is a plist using ~#:local-x~ / ~#:local-y~ (or ~#:group-local-x~ / ~#:group-local-y~) and the usual ~#:width~, ~#:height~, ~#:tile-id~, physics keys, etc.
 
-Use ~(instantiate-group-prefab registry 'name origin-x origin-y)~ from ~downstroke-prefabs~ to obtain ~(origin member ...)~. Append all of them to the scene. After moving origins (tweens and/or physics), ensure updated origins are in ~scene-entities~, then call ~(scene-sync-groups! scene)~ so every part’s ~#:x~ / ~#:y~ matches the origin plus local offsets (see ~docs/api.org~ for ordering).
+Use ~(instantiate-group-prefab registry 'name origin-x origin-y)~ from ~downstroke-prefabs~ to obtain ~(origin member ...)~. Append all of them to the scene. After moving origins (tweens and/or physics), ensure updated origins are in ~scene-entities~, then call ~(scene-sync-groups scene)~ so every part’s ~#:x~ / ~#:y~ matches the origin plus local offsets (see ~docs/api.org~ for ordering).
 
 * Entities in Scenes
 
@@ -152,17 +152,17 @@ Returns the list of all entities in the scene.
 (define all-entities (scene-entities scene))
 #+end_src
 
-** ~scene-entities-set! scene entities~
+** ~update-scene~
 
-Mutates the scene to replace the entity list. Use after ~scene-update-entities~ or batch operations.
+Returns a new scene with the specified fields changed. Preferred over the mutating ~scene-entities-set!~.
 
 #+begin_src scheme
-(scene-entities-set! scene (list updated-player updated-enemy))
+(update-scene scene entities: (list updated-player updated-enemy))
 #+end_src
 
 ** ~scene-add-entity scene entity~
 
-Adds an entity to the scene and returns the scene. Appends to the entity list.
+Returns a new scene with the entity appended to the entity list.
 
 #+begin_src scheme
 (scene-add-entity scene new-enemy)
@@ -183,17 +183,15 @@ Maps each procedure over the scene's entities, applying them in sequence. Each p
 The result is equivalent to:
 
 #+begin_src scheme
-(let* ((es (scene-entities scene))
-       (es (map apply-gravity es))
-       (es (map apply-velocity-x es))
-       (es (map apply-velocity-y es)))
-  (scene-entities-set! scene es)
-  scene)
+(chain scene
+  (scene-update-entities _ apply-gravity)
+  (scene-update-entities _ apply-velocity-x)
+  (scene-update-entities _ apply-velocity-y))
 #+end_src
 
 ** ~scene-filter-entities scene pred~
 
-Removes all entities that do not satisfy the predicate. Use to despawn dead enemies, collected items, etc.
+Keeps only entities satisfying the predicate; returns a new scene. Use to despawn dead enemies, collected items, etc.
 
 #+begin_src scheme
 ;; Remove all entities with #:health <= 0:
@@ -392,7 +390,8 @@ Here is a full example showing entity creation, initialization in the scene, and
       (let ((player (if (< (entity-ref player #:vx 0) 0)
                         (entity-set player #:facing -1)
                         (entity-set player #:facing 1))))
-        (scene-entities-set! scene (list player))))))
+        (game-scene-set! game
+          (update-scene scene entities: (list player)))))))
 #+end_src
 
-Note the let*-chaining pattern: each update builds on the previous result, keeping the data flow clear and each step testable.
+Note the let*-chaining pattern: each update builds on the previous result, keeping the data flow clear and each step testable. The single ~game-scene-set!~ at the boundary stores the final scene back on the game struct.