apl: dfn complete — guards, locals, ∇ recursion, ⍺← default (+9 tests, 235/235)

plans/apl-on-sx.md

@@ -86,8 +86,8 @@ Core mapping:
 - [x] 40+ tests in `lib/apl/tests/operators.sx`
 
 ### Phase 5 — dfns + tradfns + control flow
-- [ ] Dfn `{…}` with `⍺` (left arg, may be absent → niladic/monadic), `⍵` (right arg), `∇` (recurse), guards `cond:expr`, default left arg `⍺←default`
-- [ ] Local assignment via `←` (lexical inside dfn)
+- [x] Dfn `{…}` with `⍺` (left arg, may be absent → niladic/monadic), `⍵` (right arg), `∇` (recurse), guards `cond:expr`, default left arg `⍺←default`
+- [x] Local assignment via `←` (lexical inside dfn)
 - [ ] Tradfn `∇` header: `R←L F R;l1;l2`, statement-by-statement, branch via `→linenum`
 - [ ] Dyalog control words: `:If/:Else/:EndIf`, `:While/:EndWhile`, `:For X :In V :EndFor`, `:Select/:Case/:EndSelect`, `:Trap`/`:EndTrap`
 - [ ] Niladic / monadic / dyadic dispatch (function valence at definition time)
@@ -118,6 +118,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 2026-05-07: Phase 5 dfn complete — apl-eval-stmts (guards, locals, ⍺←default), ∇ recursion via env "nabla"; +9 tests (factorial, guards, defaults, locals); 235/235 tests
 - 2026-05-07: Phase 5 dfn foundation — lib/apl/transpile.sx with apl-eval-ast (handles :num :vec :name :monad :dyad :program :dfn) + glyph→fn lookup tables; apl-call-dfn / apl-call-dfn-m bind ⍺/⍵; ∇/guards/defaults/locals pending; 226/226 tests
 - 2026-05-07: Phase 4 step 10 — at @ (apl-at-replace + apl-at-apply); linear-index lookup, scalar-vals broadcast; 211/211 tests
 - 2026-05-07: Phase 4 step 9 — rank f⍤k (apl-rank); cell decomposition + reassembly via frame/cell shapes; 201/201 tests