purescript-lua · Unisay · Jul 7, 2026 · Jul 7, 2026 · Jul 7, 2026 · Jul 7, 2026
diff --git a/bench/goldens/fnew_Bench.CurriedStep.txt b/bench/goldens/fnew_Bench.CurriedStep.txt
@@ -9,4 +9,4 @@ function-body FNEW sites:
   Bench.CurriedStep.lua:3
   Bench.CurriedStep.lua:7
   Bench.CurriedStep.lua:10
-  Bench.CurriedStep.lua:21
+  Bench.CurriedStep.lua:23
diff --git a/bench/goldens/trace_curried_step.txt b/bench/goldens/trace_curried_step.txt
@@ -8,7 +8,7 @@ aborts (distinct site -- reason):
 bytecode end state (J*=compiled, I*=blacklisted):
   Bench.CurriedStep.lua:10 IFUNCF
   Bench.CurriedStep.lua:10 JFUNCF
-  Bench.CurriedStep.lua:15 IFUNCF
+  Bench.CurriedStep.lua:16 ILOOP
   Bench.CurriedStep.lua:3 IFUNCF
   Bench.CurriedStep.lua:3 JFUNCF
   Bench.CurriedStep.lua:7 IFUNCF

diff --git a/changelog.d/20260707_220000_unisay_loopification.md b/changelog.d/20260707_220000_unisay_loopification.md
@@ -0,0 +1,15 @@
+### Added
+
+- Self-recursive tail calls lower to `while true do` loops with parameter
+  reassignment (#181): a recursive binding — an uncurried worker or a plain
+  unary function, top-level or `let`-bound — whose tail position self-calls
+  becomes a loop, with `return go$w(e₁, e₂)` turning into the simultaneous
+  multiple assignment `p₁, p₂ = e₁, e₂`. Non-tail self-calls and other exits
+  are untouched; a body that captures a parameter inside a nested closure
+  (e.g. a CPS-style accumulator) is left recursive, since reassignment would
+  corrupt the captured environment. PUC Lua already runs these shapes in
+  constant stack via tail-call optimization, so the change is a constant
+  factor there (no per-iteration CALL/RET and argument shuffling); under
+  LuaJIT the loop is the shape the trace compiler wants, completing the
+  uncurrying story of #24 for hot recursive workers like `span` and the fold
+  fallbacks. The only observable difference is the shape of error tracebacks.
diff --git a/lib/Language/PureScript/Backend/Lua.hs b/lib/Language/PureScript/Backend/Lua.hs
@@ -25,6 +25,7 @@ import Language.PureScript.Backend.IR.Query (usesRuntimeLazy)
 import Language.PureScript.Backend.Lua.Fixture qualified as Fixture
 import Language.PureScript.Backend.Lua.Key qualified as Key
 import Language.PureScript.Backend.Lua.Linker.Foreign qualified as Foreign
+import Language.PureScript.Backend.Lua.Loopify qualified as Loopify
 import Language.PureScript.Backend.Lua.Name qualified as Lua
 import Language.PureScript.Backend.Lua.Name qualified as Name
 import Language.PureScript.Backend.Lua.Types (ParamF (..))
@@ -87,7 +88,13 @@ fromUberModule foreigns needsRuntimeLazy appOrModule uber = (`evalStateT` 0) do
               <$> fromIR foreigns Set.empty modname irExp
           pure $ DList.fromList do
             (modname, name, exp) ← recBinds
-            pure $ mkBinding modname (fromName name) exp
+            -- A self-recursive member references itself through the
+            -- module-scope table, mirroring the Ref case of 'fromIR'.
+            let self =
+                  Loopify.SelfField
+                    Fixture.moduleName
+                    (qualifyName modname (fromName name))
+            pure $ mkBinding modname (fromName name) (Loopify.loopify self exp)
 
     returnExp ←
       case appOrModule of
@@ -271,15 +278,20 @@ fromIR foreigns topLevelNames modname ir = case ir of
                         then qualifyName modname name
                         else name
                     )
-          assignments ← forM (toList grp) \(_ann, fromName → name, expr) →
+          assignments ← forM (toList grp) \(_ann, fromName → name, expr) → do
+            -- The self-reference mirrors the Ref case below: through the
+            -- module-scope table for a top-level name, plain otherwise.
+            let (target, self)
+                  | Set.member (qualifyName modname name) topLevelNames =
+                      ( qualifyName modname name
+                      , Loopify.SelfField
+                          Fixture.moduleName
+                          (qualifyName modname name)
+                      )
+                  | otherwise = (name, Loopify.SelfLocal name)
             goExp expr
-              <&> Lua.assign
-                ( Lua.VarName
-                    ( if Set.member (qualifyName modname name) topLevelNames
-                        then qualifyName modname name
-                        else name
-                    )
-                )
+              <&> Lua.assign (Lua.VarName target)
+              . Loopify.loopify self
           pure $ DList.fromList binds <> DList.fromList assignments
     pure . Left . DList.toList $
       recs <> either DList.fromList (DList.singleton . Lua.return) body