fed-sx-m1: Step 5d-pure — define_registry meta-projection fold + 16 tests

next/kernel/define_registry.erl

@@ -0,0 +1,68 @@
+-module(define_registry).
+-export([fold/2, fold_fn/0, define_kind/1]).
+
+%% Define-registry projection fold — Erlang-fun stand-in for the
+%% genesis `define-registry.sx` body. The intent is identical: a
+%% projection whose state is a registry-shaped property list, fed
+%% by every `Create{Define*{...}}` activity. The SX body would
+%% eventually replace this once an SX-source eval bridge lets the
+%% kernel evaluate the genesis fold directly; until then this
+%% Erlang module proves the meta-projection mechanism wires
+%% through `projection:fold_fn` and `nx_kernel` cleanly.
+%%
+%% State shape mirrors `registry:new()` exactly:
+%%   [{Kind, [{Name, Entry}, ...]}, ...]
+%% so callers can use `registry:lookup/3` etc. on the result.
+%%
+%% Type discrimination uses atoms (`define_activity`, …). Real SX
+%% would carry the string forms ("DefineActivity", …); the bridge
+%% will translate. See define_kind/1 for the mapping.
+
+fold(Activity, State) ->
+    case envelope:get_field(type, Activity) of
+        {ok, create} -> fold_create(Activity, State);
+        _ -> State
+    end.
+
+fold_create(Activity, State) ->
+    case envelope:get_field(object, Activity) of
+        {ok, Obj} ->
+            case envelope:get_field(type, Obj) of
+                {ok, ObjType} ->
+                    case define_kind(ObjType) of
+                        not_a_define -> State;
+                        Kind -> fold_register(Kind, Obj, State)
+                    end;
+                _ -> State
+            end;
+        _ -> State
+    end.
+
+fold_register(Kind, Obj, State) ->
+    case envelope:get_field(name, Obj) of
+        {ok, Name} ->
+            case registry:register(Kind, Name, Obj, State) of
+                {ok, NewState}     -> NewState;
+                {error, unknown_kind} -> State
+            end;
+        not_found -> State
+    end.
+
+%% fold_fn/0 — a 2-arity Erlang fun the projection module plants
+%% in its record's :fold slot. Lets `projection:start_link/3`
+%% wire define-registry directly.
+fold_fn() ->
+    fun (Activity, State) -> fold(Activity, State) end.
+
+%% define_kind/1 — discriminator from the inner Define* object's
+%% :type atom to the registry kind atom. Anything unrecognised
+%% returns not_a_define so the fold treats it as a pass-through.
+
+define_kind(define_activity)   -> activity_types;
+define_kind(define_object)     -> object_types;
+define_kind(define_projection) -> projections;
+define_kind(define_validator)  -> validators;
+define_kind(define_codec)      -> codecs;
+define_kind(define_sig_suite)  -> sig_suites;
+define_kind(define_audience)   -> audience;
+define_kind(_)                 -> not_a_define.