haskell: runtime constructor registry (+24 tests, 250/250)

plans/haskell-on-sx.md

@@ -69,7 +69,7 @@ Key mappings:
 
 ### Phase 2 — desugar + eager-ish eval + ADTs (untyped)
 - [x] Desugar: guards → nested `if`s; `where` → `let`; list comp → `concatMap`-based; do-notation stays for now (desugared in phase 3)
-- [ ] `data` declarations register constructors in runtime
+- [x] `data` declarations register constructors in runtime
 - [ ] Pattern match (tag-based, value-level): atoms, vars, wildcards, constructor patterns, `as` patterns, nested
 - [ ] Evaluator (still strict internally — laziness in phase 3): `let`, `lambda`, application, `case`, literals, constructors
 - [ ] 30+ eval tests in `lib/haskell/tests/eval.sx`
@@ -114,6 +114,26 @@ Key mappings:
 
 _Newest first._
 
+- **2026-04-24** — Phase 2: runtime constructor registry
+  (`lib/haskell/runtime.sx`). A mutable dict `hk-constructors` keyed
+  by constructor name, each entry carrying arity and owning type.
+  `hk-register-data!` walks a `:data` AST and registers every
+  `:con-def` with its arity (= number of field types) and the type
+  name; `hk-register-newtype!` does the one-constructor variant;
+  `hk-register-decls!` / `hk-register-program!` filter a decls list
+  (or a `:program` / `:module` AST) and call the appropriate
+  registrar. `hk-load-source!` composes it with `hk-core`
+  (tokenize → layout → parse → desugar → register). Pre-registers
+  five built-ins tied to Haskell syntactic forms: `True` / `False`
+  (Bool), `[]` and `:` (List), `()` (Unit) — everything else comes
+  from user declarations or the eventual Prelude. Query helpers:
+  `hk-is-con?`, `hk-con-arity`, `hk-con-type`, `hk-con-names`. 24
+  new tests in `lib/haskell/tests/runtime.sx` cover each built-in
+  (arity + type), unknown-name probes, registration of `MyBool` /
+  `Maybe` / `Either` / recursive `Tree` / `newtype Age`, multi-data
+  programs, a module-header body, ignoring non-data decls, and
+  last-wins re-registration. 250/250 green.
+
 - **2026-04-24** — Phase 2 kicks off with `lib/haskell/desugar.sx` — a
   tree-walking rewriter that eliminates the three surface-only forms
   produced by the parser, leaving a smaller core AST for the evaluator: