From e224fb2db01ab6cca4dce4ed0dedb0dadb81349c Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Fri, 24 Apr 2026 18:05:35 +0000
Subject: [PATCH] lua: pcall/xpcall/error via guard+raise; arity-dispatch
 lua-apply +9 tests

---
 lib/lua/runtime.sx | 52 ++++++++++++++++++++++++++++++++++++++++++++--
 lib/lua/test.sh    | 33 +++++++++++++++++++++++++++++
 plans/lua-on-sx.md |  3 ++-
 3 files changed, 85 insertions(+), 3 deletions(-)

diff --git a/lib/lua/runtime.sx b/lib/lua/runtime.sx
index 445852b2..6a6f2fc7 100644
--- a/lib/lua/runtime.sx
+++ b/lib/lua/runtime.sx
@@ -384,6 +384,24 @@
 
 (define sx-apply-ref apply)
 
+(define
+  lua-apply
+  (fn
+    (f rargs)
+    (let
+      ((n (len rargs)))
+      (cond
+        ((= n 0) (f))
+        ((= n 1) (f (nth rargs 0)))
+        ((= n 2) (f (nth rargs 0) (nth rargs 1)))
+        ((= n 3) (f (nth rargs 0) (nth rargs 1) (nth rargs 2)))
+        ((= n 4) (f (nth rargs 0) (nth rargs 1) (nth rargs 2) (nth rargs 3)))
+        ((= n 5) (f (nth rargs 0) (nth rargs 1) (nth rargs 2) (nth rargs 3) (nth rargs 4)))
+        ((= n 6) (f (nth rargs 0) (nth rargs 1) (nth rargs 2) (nth rargs 3) (nth rargs 4) (nth rargs 5)))
+        ((= n 7) (f (nth rargs 0) (nth rargs 1) (nth rargs 2) (nth rargs 3) (nth rargs 4) (nth rargs 5) (nth rargs 6)))
+        ((= n 8) (f (nth rargs 0) (nth rargs 1) (nth rargs 2) (nth rargs 3) (nth rargs 4) (nth rargs 5) (nth rargs 6) (nth rargs 7)))
+        (else (sx-apply-ref f rargs))))))
+
 (define
   lua-call
   (fn
@@ -392,11 +410,41 @@
       ((f (first args)) (rargs (rest args)))
       (cond
         ((or (= (type-of f) "function") (= (type-of f) "lambda"))
-          (sx-apply-ref f rargs))
+          (lua-apply f rargs))
         ((= (type-of f) "dict")
           (let
             ((m (lua-get-mm f "__call")))
             (cond
               ((= m nil) (error "lua: attempt to call non-function"))
-              (else (sx-apply-ref m (cons f rargs))))))
+              (else (lua-apply m (cons f rargs))))))
         (else (error "lua: attempt to call non-function"))))))
+
+(define lua-error (fn (&rest args) (raise (first args))))
+
+(define error lua-error)
+
+(define
+  pcall
+  (fn
+    (&rest args)
+    (let
+      ((f (first args)) (rargs (rest args)))
+      (guard
+        (e (true (list (quote lua-multi) false e)))
+        (let
+          ((r (lua-apply f rargs)))
+          (cond
+            ((lua-multi? r) (cons (quote lua-multi) (cons true (rest r))))
+            (else (list (quote lua-multi) true r))))))))
+
+(define
+  xpcall
+  (fn
+    (f msgh)
+    (guard
+      (e (true (list (quote lua-multi) false (lua-first (lua-apply msgh (list e))))))
+      (let
+        ((r (lua-apply f (list))))
+        (cond
+          ((lua-multi? r) (cons (quote lua-multi) (cons true (rest r))))
+          (else (list (quote lua-multi) true r)))))))
diff --git a/lib/lua/test.sh b/lib/lua/test.sh
index f75e0262..e390bf6b 100755
--- a/lib/lua/test.sh
+++ b/lib/lua/test.sh
@@ -659,6 +659,28 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 880)
 (eval "(lua-eval-ast \"local Animal = {} Animal.__index = Animal function Animal:new(name) local o = setmetatable({name = name}, self) return o end function Animal:getName() return self.name end local a = Animal:new(\\\"Rex\\\") return a:getName()\")")
 
+;; ── Phase 4: pcall / xpcall / error ────────────────────────────
+(epoch 900)
+(eval "(lua-eval-ast \"local ok, err = pcall(function() error(\\\"boom\\\") end) if ok then return 0 else return err end\")")
+(epoch 901)
+(eval "(lua-eval-ast \"local ok, v = pcall(function() return 42 end) if ok then return v else return -1 end\")")
+(epoch 902)
+(eval "(lua-eval-ast \"local ok, a, b = pcall(function() return 1, 2 end) return (ok and a + b) or 0\")")
+(epoch 903)
+(eval "(lua-eval-ast \"local function div(a, b) if b == 0 then error(\\\"div by zero\\\") end return a / b end local ok, r = pcall(div, 10, 2) if ok then return r else return -1 end\")")
+(epoch 904)
+(eval "(lua-eval-ast \"local function div(a, b) if b == 0 then error(\\\"div by zero\\\") end return a / b end local ok, e = pcall(div, 10, 0) if ok then return \\\"no\\\" else return e end\")")
+(epoch 905)
+(eval "(lua-eval-ast \"local function f() error({code = 42}) end local ok, err = pcall(f) return err.code\")")
+(epoch 906)
+(eval "(lua-eval-ast \"local ok1, e1 = pcall(function() local ok2, e2 = pcall(function() error(\\\"inner\\\") end) if not ok2 then error(\\\"outer:\\\" .. e2) end end) return e1\")")
+
+;; xpcall
+(epoch 910)
+(eval "(lua-eval-ast \"local function f() error(\\\"raw\\\") end local function handler(e) return \\\"H:\\\" .. e end local ok, v = xpcall(f, handler) if ok then return \\\"no\\\" else return v end\")")
+(epoch 911)
+(eval "(lua-eval-ast \"local function f() return 99 end local function handler(e) return e end local ok, v = xpcall(f, handler) return v\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -989,6 +1011,17 @@ check 860 "__call"                          '105'
 check 870 "__len"                           '99'
 check 880 "OO pattern self:m()"             '"Rex"'
 
+# ── Phase 4: pcall / xpcall / error ───────────────────────────
+check 900 "pcall catches error(msg)"        '"boom"'
+check 901 "pcall ok path single val"        '42'
+check 902 "pcall ok path multi val"         '3'
+check 903 "pcall with args, ok"             '5'
+check 904 "pcall with args, err"            '"div by zero"'
+check 905 "error(table) preserved"          '42'
+check 906 "nested pcall"                    '"outer:inner"'
+check 910 "xpcall invokes handler"          '"H:raw"'
+check 911 "xpcall ok path"                  '99'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL Lua-on-SX tests passed"
diff --git a/plans/lua-on-sx.md b/plans/lua-on-sx.md
index a99eb41b..fc3766b4 100644
--- a/plans/lua-on-sx.md
+++ b/plans/lua-on-sx.md
@@ -61,7 +61,7 @@ Each item: implement → tests → tick box → update progress log.
 
 ### Phase 4 — metatables + error handling (next run)
 - [x] Metatable dispatch: `__index`, `__newindex`, `__add`/`__sub`/…, `__eq`, `__lt`, `__call`, `__tostring`, `__len`
-- [ ] `pcall`/`xpcall`/`error` via handler-bind
+- [x] `pcall`/`xpcall`/`error` via handler-bind
 - [ ] Generic `for … in …`
 
 ### Phase 5 — coroutines (the showcase)
@@ -82,6 +82,7 @@ Each item: implement → tests → tick box → update progress log.
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-24: lua: `pcall`/`xpcall`/`error` via SX `guard` + `raise`. Added `lua-apply` (arity-dispatch 0-8, apply fallback) because SX `apply` re-wraps raises as "Unhandled exception". Table payloads preserved (`error({code = 42})`). 256 total tests.
 - 2026-04-24: lua: phase 4 — metatable dispatch (`__index`/`__newindex`/arith/compare/`__call`/`__len`), `setmetatable`/`getmetatable`/`type` globals, OO `self:method` pattern. Transpile routes all calls through `lua-call` (stashed `sx-apply-ref` to dodge user-shadowing of SX `apply`). Skipped `__tostring` (needs `tostring()` builtin). 247 total tests.
 - 2026-04-24: lua: PUC-Rio scoreboard baseline — 0/16 runnable pass (0.0%). Top modes: 14× parse error, 1× `print` undef, 1× vararg transpile. Phase 3 complete.
 - 2026-04-24: lua: conformance runner — `conformance.sh` shim + `conformance.py` (long-lived sx_server, epoch protocol, classify_error, writes scoreboard.{json,md}). 24 files classified in full run: 8 skip / 16 fail / 0 timeout.