From ecdc42b307a8237f95c30e75d9e0268966ec41aa Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Thu, 22 Jun 2023 16:34:06 +0300
Subject: [PATCH 01/14] Semantics

---
 src/PureScript/Backend/Optimizer/Convert.purs |  2 +-
 .../Backend/Optimizer/Semantics.purs          | 20 +++++++++++++++----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/PureScript/Backend/Optimizer/Convert.purs b/src/PureScript/Backend/Optimizer/Convert.purs
index 04f68146..6cfaed93 100644
--- a/src/PureScript/Backend/Optimizer/Convert.purs
+++ b/src/PureScript/Backend/Optimizer/Convert.purs
@@ -234,7 +234,7 @@ toBackendTopLevelBindingGroup env = case _ of
 
 toTopLevelBackendBinding :: Array (Qualified Ident) -> ConvertEnv -> Binding Ann -> Accum ConvertEnv (Tuple Ident (WithDeps NeutralExpr))
 toTopLevelBackendBinding group env (Binding _ ident cfn) = do
-  let evalEnv = Env { currentModule: env.currentModule, evalExtern: makeExternEval env, locals: [], directives: env.directives }
+  let evalEnv = Env { currentModule: env.currentModule, evalExtern: makeExternEval env, locals: [], punt: Set.empty, directives: env.directives }
   let backendExpr = toBackendExpr cfn env
   let Tuple impl expr' = toExternImpl env group (optimize (getCtx env) evalEnv (Qualified (Just env.currentModule) ident) env.rewriteLimit backendExpr)
   { accum: env
diff --git a/src/PureScript/Backend/Optimizer/Semantics.purs b/src/PureScript/Backend/Optimizer/Semantics.purs
index 24f9d360..5062c72f 100644
--- a/src/PureScript/Backend/Optimizer/Semantics.purs
+++ b/src/PureScript/Backend/Optimizer/Semantics.purs
@@ -48,6 +48,7 @@ data BackendSemantics
   | NeutLocal (Maybe Ident) Level
   | NeutVar (Qualified Ident)
   | NeutStop (Qualified Ident)
+  | RecurseWithRecklessAbandon (Qualified Ident)
   | NeutData (Qualified Ident) ConstructorType ProperName Ident (Array (Tuple String BackendSemantics))
   | NeutCtorDef (Qualified Ident) ConstructorType ProperName Ident (Array String)
   | NeutApp BackendSemantics (Spine BackendSemantics)
@@ -86,6 +87,7 @@ data BackendRewrite
   | RewriteLetAssoc (Array (LetBindingAssoc BackendExpr)) BackendExpr
   | RewriteEffectBindAssoc (Array (EffectBindingAssoc BackendExpr)) BackendExpr
   | RewriteStop (Qualified Ident)
+  | RewriteRecurse (Qualified Ident)
   | RewriteUnpackOp (Maybe Ident) Level UnpackOp BackendExpr
   | RewriteDistBranchesLet (Maybe Ident) Level (NonEmptyArray (Pair BackendExpr)) BackendExpr BackendExpr
   | RewriteDistBranchesOp (NonEmptyArray (Pair BackendExpr)) BackendExpr DistOp
@@ -164,6 +166,7 @@ newtype Env = Env
   , evalExtern :: Env -> Qualified Ident -> Array ExternSpine -> Maybe BackendSemantics
   , locals :: Array (LocalBinding BackendSemantics)
   , directives :: InlineDirectiveMap
+  , punt :: Set.Set (Qualified Ident)
   }
 
 derive instance Newtype Env _
@@ -195,13 +198,18 @@ addStop (Env env) ref acc = Env env
       env.directives
   }
 
+puntMe :: Env -> Array (Qualified Ident) -> Env
+puntMe (Env env) quals = Env env
+  { punt = Set.union env.punt (Set.fromFoldable quals)
+  }
 class Eval f where
   eval :: Env -> f -> BackendSemantics
 
 instance Eval f => Eval (BackendSyntax f) where
-  eval env = case _ of
-    Var qual ->
-      evalExtern env qual []
+  eval env@(Env { punt }) = case _ of
+    Var qual
+      | qual `Set.member` punt -> RecurseWithRecklessAbandon qual
+      | otherwise -> evalExtern env qual []
     Local ident lvl ->
       case lookupLocal env lvl of
         Just (One sem) -> sem
@@ -279,6 +287,7 @@ instance Eval BackendExpr where
     go env = case _ of
       ExprRewrite _ rewrite ->
         case rewrite of
+          RewriteRecurse ident -> eval env (Var ident :: BackendSyntax BackendExpr)
           RewriteInline _ _ binding body ->
             go (bindLocal env (One (eval env binding))) body
           RewriteUncurry ident _ args binding body ->
@@ -846,7 +855,7 @@ evalExternFromImpl env@(Env e) qual (Tuple analysis impl) spine = case spine of
           Just InlineNever ->
             Just $ NeutStop qual
           Just InlineAlways ->
-            Just $ eval (envForGroup env ref InlineRef group) expr
+            Just $ eval (puntMe env group) expr
           Just (InlineArity _) ->
             Nothing
           _ ->
@@ -1056,6 +1065,7 @@ quote = go
       foldr (buildBranchCond ctx) (quote ctx <<< force $ def) branches'
 
     -- Non-block constructors
+    RecurseWithRecklessAbandon ident -> ExprRewrite (withRewrite (analyzeDefault ctx (Var ident))) $ RewriteRecurse ident
     SemExtern _ _ sem ->
       go ctx (force sem)
     SemLam ident k -> do
@@ -1529,6 +1539,8 @@ freeze init = Tuple (analysisOf init) (go init)
           NeutralExpr $ Let ident level (NeutralExpr (Abs args (go binding))) (go body)
         RewriteStop qual ->
           NeutralExpr $ Var qual
+        RewriteRecurse qual ->
+          NeutralExpr $ Var qual
         RewriteLetAssoc bindings body ->
           case NonEmptyArray.fromArray bindings of
             Just bindings' -> do

From 258d1ad1951d2dc1bd1584632e8fa3eb36198665 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Thu, 22 Jun 2023 16:36:22 +0300
Subject: [PATCH 02/14] Adds test

---
 .../Snapshot.RecursionInlined01.js            | 24 +++++++++++++++++++
 .../Snapshot.RecursionInlined01.purs          | 14 +++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
 create mode 100644 backend-es/test/snapshots/Snapshot.RecursionInlined01.purs

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
new file mode 100644
index 00000000..7549c484
--- /dev/null
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
@@ -0,0 +1,24 @@
+// @inline Snapshot.RecursionInlined01.append always
+import * as $runtime from "../runtime.js";
+const $List = (tag, _1, _2) => ({tag, _1, _2});
+const Nil = /* #__PURE__ */ $List("Nil");
+const Cons = value0 => value1 => $List("Cons", value0, value1);
+const append = v => v1 => {
+  if (v.tag === "Nil") { return v1; }
+  if (v.tag === "Cons") { return $List("Cons", v._1, append(v._2)(v1)); }
+  $runtime.fail();
+};
+const main = /* #__PURE__ */ $List(
+  "Cons",
+  "a",
+  /* #__PURE__ */ $List(
+    "Cons",
+    "b",
+    /* #__PURE__ */ $List(
+      "Cons",
+      "c",
+      /* #__PURE__ */ $List("Cons", "d", /* #__PURE__ */ $List("Cons", "e", /* #__PURE__ */ $List("Cons", "f", /* #__PURE__ */ $List("Cons", "g", Nil))))
+    )
+  )
+);
+export {$List, Cons, Nil, append, main};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
new file mode 100644
index 00000000..ff3a3297
--- /dev/null
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
@@ -0,0 +1,14 @@
+-- @inline Snapshot.RecursionInlined01.append always
+module Snapshot.RecursionInlined01 where
+
+data List a = Nil | Cons a (List a)
+infixr 5 Cons as :
+
+append :: forall a. List a -> List a -> List a
+append Nil ys = ys
+append (Cons x xs) ys = Cons x (append xs ys)
+
+infixr 4 append as <>
+
+main :: List String
+main = ("a" : "b" : "c" : "d" : "e" : "f" : "g" : Nil) <> Nil
\ No newline at end of file

From a379b41e3435597e92cbd8b089b1c477d791deb5 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Thu, 22 Jun 2023 18:31:22 +0300
Subject: [PATCH 03/14] Adds a couple more cases

---
 src/PureScript/Backend/Optimizer/Semantics.purs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/PureScript/Backend/Optimizer/Semantics.purs b/src/PureScript/Backend/Optimizer/Semantics.purs
index 5062c72f..3c834e5a 100644
--- a/src/PureScript/Backend/Optimizer/Semantics.purs
+++ b/src/PureScript/Backend/Optimizer/Semantics.purs
@@ -861,9 +861,9 @@ evalExternFromImpl env@(Env e) qual (Tuple analysis impl) spine = case spine of
           _ ->
             case expr of
               NeutralExpr (Lit lit) | shouldInlineExternLiteral lit ->
-                Just $ eval (envForGroup env ref InlineRef group) expr
+                Just $ eval (puntMe env group) expr
               _ | shouldInlineExternReference qual analysis expr ->
-                Just $ eval (envForGroup env ref InlineRef group) expr
+                Just $ eval (puntMe env group) expr
               _ ->
                 Nothing
       ExternCtor _ ct ty tag [] ->

From 504b08d625820ff6b90ade2864510dc1add8f9a6 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Sun, 25 Jun 2023 10:57:12 +0300
Subject: [PATCH 04/14] Renames main to test1

---
 backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js | 4 ++--
 backend-es/test/snapshots/Snapshot.RecursionInlined01.purs   | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
index 7549c484..344e9e68 100644
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
@@ -8,7 +8,7 @@ const append = v => v1 => {
   if (v.tag === "Cons") { return $List("Cons", v._1, append(v._2)(v1)); }
   $runtime.fail();
 };
-const main = /* #__PURE__ */ $List(
+const test1 = /* #__PURE__ */ $List(
   "Cons",
   "a",
   /* #__PURE__ */ $List(
@@ -21,4 +21,4 @@ const main = /* #__PURE__ */ $List(
     )
   )
 );
-export {$List, Cons, Nil, append, main};
+export {$List, Cons, Nil, append, test1};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
index ff3a3297..8fb8624d 100644
--- a/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
@@ -10,5 +10,5 @@ append (Cons x xs) ys = Cons x (append xs ys)
 
 infixr 4 append as <>
 
-main :: List String
-main = ("a" : "b" : "c" : "d" : "e" : "f" : "g" : Nil) <> Nil
\ No newline at end of file
+test1 :: List String
+test1 = ("a" : "b" : "c" : "d" : "e" : "f" : "g" : Nil) <> Nil
\ No newline at end of file

From c10bc8e834d9274d38a04958f2dc86d5fa9a2447 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 11:22:23 +0300
Subject: [PATCH 05/14] Adds first guard

---
 src/PureScript/Backend/Optimizer/Convert.purs |  2 +-
 .../Backend/Optimizer/Semantics.purs          | 29 +++++++++++++++----
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/PureScript/Backend/Optimizer/Convert.purs b/src/PureScript/Backend/Optimizer/Convert.purs
index 6cfaed93..b21c56a5 100644
--- a/src/PureScript/Backend/Optimizer/Convert.purs
+++ b/src/PureScript/Backend/Optimizer/Convert.purs
@@ -234,7 +234,7 @@ toBackendTopLevelBindingGroup env = case _ of
 
 toTopLevelBackendBinding :: Array (Qualified Ident) -> ConvertEnv -> Binding Ann -> Accum ConvertEnv (Tuple Ident (WithDeps NeutralExpr))
 toTopLevelBackendBinding group env (Binding _ ident cfn) = do
-  let evalEnv = Env { currentModule: env.currentModule, evalExtern: makeExternEval env, locals: [], punt: Set.empty, directives: env.directives }
+  let evalEnv = Env { currentModule: env.currentModule, evalExtern: makeExternEval env, locals: [], punt: Set.empty, directives: env.directives, blockNextRecursion: false }
   let backendExpr = toBackendExpr cfn env
   let Tuple impl expr' = toExternImpl env group (optimize (getCtx env) evalEnv (Qualified (Just env.currentModule) ident) env.rewriteLimit backendExpr)
   { accum: env
diff --git a/src/PureScript/Backend/Optimizer/Semantics.purs b/src/PureScript/Backend/Optimizer/Semantics.purs
index 3c834e5a..94475803 100644
--- a/src/PureScript/Backend/Optimizer/Semantics.purs
+++ b/src/PureScript/Backend/Optimizer/Semantics.purs
@@ -167,6 +167,7 @@ newtype Env = Env
   , locals :: Array (LocalBinding BackendSemantics)
   , directives :: InlineDirectiveMap
   , punt :: Set.Set (Qualified Ident)
+  , blockNextRecursion :: Boolean
   }
 
 derive instance Newtype Env _
@@ -186,6 +187,15 @@ insertDirective ref acc dir = Map.alter
       Just $ Map.singleton acc dir
   ref
 
+recursable :: Array BackendSemantics -> Boolean
+recursable = go
+  where
+  go arr
+    | Just { head, tail } <- Array.uncons arr = case head of
+        NeutData _ _ _ _ _ -> true && go tail
+        _ -> false
+    | otherwise = true
+
 addStop :: Env -> EvalRef -> InlineAccessor -> Env
 addStop (Env env) ref acc = Env env
   { directives = Map.alter
@@ -202,11 +212,12 @@ puntMe :: Env -> Array (Qualified Ident) -> Env
 puntMe (Env env) quals = Env env
   { punt = Set.union env.punt (Set.fromFoldable quals)
   }
+
 class Eval f where
   eval :: Env -> f -> BackendSemantics
 
 instance Eval f => Eval (BackendSyntax f) where
-  eval env@(Env { punt }) = case _ of
+  eval env@(Env envx@{ punt }) = case _ of
     Var qual
       | qual `Set.member` punt -> RecurseWithRecklessAbandon qual
       | otherwise -> evalExtern env qual []
@@ -217,8 +228,11 @@ instance Eval f => Eval (BackendSyntax f) where
           force sem
         _ ->
           unsafeCrashWith $ "Unbound local at level " <> show (unwrap lvl)
-    App hd tl ->
-      evalApp env (eval env hd) (NonEmptyArray.toArray (eval env <$> tl))
+    App hd tl -> do
+      let tailEvaled = NonEmptyArray.toArray (eval env <$> tl)
+      let canRecurse = recursable tailEvaled
+      let headEvaled = eval (Env envx { blockNextRecursion = not canRecurse }) hd
+      evalApp env headEvaled tailEvaled
     UncurriedApp hd tl ->
       evalUncurriedApp env (eval env hd) (eval env <$> tl)
     UncurriedAbs idents body -> do
@@ -282,12 +296,12 @@ instance Eval f => Eval (BackendSyntax f) where
       guardFailOver snd (map (eval env) <$> fields) $ NeutData qual ct ty tag
 
 instance Eval BackendExpr where
-  eval = go
+  eval (Env e@{ blockNextRecursion }) = go (Env e { blockNextRecursion = false })
     where
     go env = case _ of
       ExprRewrite _ rewrite ->
         case rewrite of
-          RewriteRecurse ident -> eval env (Var ident :: BackendSyntax BackendExpr)
+          RewriteRecurse ident -> if blockNextRecursion then mkSemExtern ident [] else eval env (Var ident :: BackendSyntax BackendExpr)
           RewriteInline _ _ binding body ->
             go (bindLocal env (One (eval env binding))) body
           RewriteUncurry ident _ args binding body ->
@@ -835,9 +849,12 @@ primOpOrdNot = case _ of
   OpGt -> OpLte
   OpGte -> OpLt
 
+mkSemExtern :: Qualified Ident -> Array ExternSpine -> BackendSemantics
+mkSemExtern qual spine = SemExtern qual spine (defer \_ -> neutralSpine (NeutVar qual) spine)
+
 evalExtern :: Env -> Qualified Ident -> Array ExternSpine -> BackendSemantics
 evalExtern env@(Env e) qual spine = case e.evalExtern env qual spine of
-  Nothing -> SemExtern qual spine (defer \_ -> neutralSpine (NeutVar qual) spine)
+  Nothing -> mkSemExtern qual spine
   Just sem -> sem
 
 envForGroup :: Env -> EvalRef -> InlineAccessor -> Array (Qualified Ident) -> Env

From 30b82a5b480fea81efe18e92a7875f20a87cedfa Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 11:26:05 +0300
Subject: [PATCH 06/14] Adds test

---
 .../Snapshot.RecursionInlined02.js            | 44 +++++++++++++++++++
 .../Snapshot.RecursionInlined02.purs          | 14 ++++++
 2 files changed, 58 insertions(+)
 create mode 100644 backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
 create mode 100644 backend-es/test/snapshots/Snapshot.RecursionInlined02.purs

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
new file mode 100644
index 00000000..d5871c39
--- /dev/null
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
@@ -0,0 +1,44 @@
+// @inline Snapshot.RecursionInlined02.append always
+import * as $runtime from "../runtime.js";
+const $List = (tag, _1, _2) => ({tag, _1, _2});
+const Nil = /* #__PURE__ */ $List("Nil");
+const Cons = value0 => value1 => $List("Cons", value0, value1);
+const append = v => v1 => {
+  if (v.tag === "Nil") { return v1; }
+  if (v.tag === "Cons") { return $List("Cons", v._1, append(v._2)(v1)); }
+  $runtime.fail();
+};
+const test1 = z => $List(
+  "Cons",
+  "a",
+  $List(
+    "Cons",
+    "b",
+    $List(
+      "Cons",
+      "c",
+      $List(
+        "Cons",
+        "d",
+        $List(
+          "Cons",
+          "e",
+          $List(
+            "Cons",
+            "f",
+            $List(
+              "Cons",
+              "g",
+              (() => {
+                if (z.tag === "Nil") { return Nil; }
+                if (z.tag === "Cons") { return $List("Cons", z._1, append(z._2)(Nil)); }
+                $runtime.fail();
+              })()
+            )
+          )
+        )
+      )
+    )
+  )
+);
+export {$List, Cons, Nil, append, test1};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
new file mode 100644
index 00000000..8478a151
--- /dev/null
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
@@ -0,0 +1,14 @@
+-- @inline Snapshot.RecursionInlined02.append always
+module Snapshot.RecursionInlined02 where
+
+data List a = Nil | Cons a (List a)
+infixr 5 Cons as :
+
+append :: forall a. List a -> List a -> List a
+append Nil ys = ys
+append (Cons x xs) ys = Cons x (append xs ys)
+
+infixr 4 append as <>
+
+test1 :: List String -> List String
+test1 z = ("a" : "b" : "c" : "d" : "e" : "f" : "g" : z) <> Nil
\ No newline at end of file

From daf524124c161128ab5060fbc02cceff8a3a089f Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 11:42:56 +0300
Subject: [PATCH 07/14] Removes spurious true

---
 src/PureScript/Backend/Optimizer/Semantics.purs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/PureScript/Backend/Optimizer/Semantics.purs b/src/PureScript/Backend/Optimizer/Semantics.purs
index 94475803..133bc707 100644
--- a/src/PureScript/Backend/Optimizer/Semantics.purs
+++ b/src/PureScript/Backend/Optimizer/Semantics.purs
@@ -192,7 +192,7 @@ recursable = go
   where
   go arr
     | Just { head, tail } <- Array.uncons arr = case head of
-        NeutData _ _ _ _ _ -> true && go tail
+        NeutData _ _ _ _ _ -> go tail
         _ -> false
     | otherwise = true
 

From 4e2603482728a02dc6394519dddc9ddf234600da Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 12:01:00 +0300
Subject: [PATCH 08/14] Shrinks to one test

---
 .../Snapshot.RecursionInlined01.js            | 19 +++++++-
 .../Snapshot.RecursionInlined02.js            | 44 -------------------
 .../Snapshot.RecursionInlined01.purs          |  4 +-
 .../Snapshot.RecursionInlined02.purs          | 14 ------
 4 files changed, 21 insertions(+), 60 deletions(-)
 delete mode 100644 backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
 delete mode 100644 backend-es/test/snapshots/Snapshot.RecursionInlined02.purs

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
index 344e9e68..1a780ffd 100644
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined01.js
@@ -21,4 +21,21 @@ const test1 = /* #__PURE__ */ $List(
     )
   )
 );
-export {$List, Cons, Nil, append, test1};
+const test2 = z => $List(
+  "Cons",
+  "a",
+  $List(
+    "Cons",
+    "b",
+    $List(
+      "Cons",
+      "c",
+      (() => {
+        if (z.tag === "Nil") { return $List("Cons", "d", $List("Cons", "e", $List("Cons", "f", $List("Cons", "g", Nil)))); }
+        if (z.tag === "Cons") { return $List("Cons", z._1, append(z._2)($List("Cons", "d", $List("Cons", "e", $List("Cons", "f", $List("Cons", "g", Nil)))))); }
+        $runtime.fail();
+      })()
+    )
+  )
+);
+export {$List, Cons, Nil, append, test1, test2};
diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
deleted file mode 100644
index d5871c39..00000000
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
+++ /dev/null
@@ -1,44 +0,0 @@
-// @inline Snapshot.RecursionInlined02.append always
-import * as $runtime from "../runtime.js";
-const $List = (tag, _1, _2) => ({tag, _1, _2});
-const Nil = /* #__PURE__ */ $List("Nil");
-const Cons = value0 => value1 => $List("Cons", value0, value1);
-const append = v => v1 => {
-  if (v.tag === "Nil") { return v1; }
-  if (v.tag === "Cons") { return $List("Cons", v._1, append(v._2)(v1)); }
-  $runtime.fail();
-};
-const test1 = z => $List(
-  "Cons",
-  "a",
-  $List(
-    "Cons",
-    "b",
-    $List(
-      "Cons",
-      "c",
-      $List(
-        "Cons",
-        "d",
-        $List(
-          "Cons",
-          "e",
-          $List(
-            "Cons",
-            "f",
-            $List(
-              "Cons",
-              "g",
-              (() => {
-                if (z.tag === "Nil") { return Nil; }
-                if (z.tag === "Cons") { return $List("Cons", z._1, append(z._2)(Nil)); }
-                $runtime.fail();
-              })()
-            )
-          )
-        )
-      )
-    )
-  )
-);
-export {$List, Cons, Nil, append, test1};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
index 8fb8624d..38657386 100644
--- a/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined01.purs
@@ -11,4 +11,6 @@ append (Cons x xs) ys = Cons x (append xs ys)
 infixr 4 append as <>
 
 test1 :: List String
-test1 = ("a" : "b" : "c" : "d" : "e" : "f" : "g" : Nil) <> Nil
\ No newline at end of file
+test1 = ("a" : "b" : "c" : Nil) <> ("d" : "e" : "f" : "g" : Nil)
+test2 :: List String -> List String
+test2 z = ("a" : "b" : "c" : z) <> ("d" : "e" : "f" : "g" : Nil)
\ No newline at end of file
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
deleted file mode 100644
index 8478a151..00000000
--- a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
+++ /dev/null
@@ -1,14 +0,0 @@
--- @inline Snapshot.RecursionInlined02.append always
-module Snapshot.RecursionInlined02 where
-
-data List a = Nil | Cons a (List a)
-infixr 5 Cons as :
-
-append :: forall a. List a -> List a -> List a
-append Nil ys = ys
-append (Cons x xs) ys = Cons x (append xs ys)
-
-infixr 4 append as <>
-
-test1 :: List String -> List String
-test1 z = ("a" : "b" : "c" : "d" : "e" : "f" : "g" : z) <> Nil
\ No newline at end of file

From fa03c933ea999c3e5db5054727de6c950cd81fd2 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 12:12:48 +0300
Subject: [PATCH 09/14] Adds NeutLit to guard

---
 .../Snapshot.RecursionInlined02.js              | 16 ++++++++++++++++
 .../snapshots/Snapshot.RecursionInlined02.purs  | 17 +++++++++++++++++
 src/PureScript/Backend/Optimizer/Semantics.purs |  1 +
 3 files changed, 34 insertions(+)
 create mode 100644 backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
 create mode 100644 backend-es/test/snapshots/Snapshot.RecursionInlined02.purs

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
new file mode 100644
index 00000000..6a873805
--- /dev/null
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
@@ -0,0 +1,16 @@
+// @inline Snapshot.RecursionInlined02.addStuff always
+const $List = (tag, _1, _2) => ({tag, _1, _2});
+const Nil = /* #__PURE__ */ $List("Nil");
+const Cons = value0 => value1 => $List("Cons", value0, value1);
+const addStuff = x => ys => {
+  if (x === 0) { return ys; }
+  return 1 + addStuff(x - 1 | 0)(ys) | 0;
+};
+const test1 = 7;
+const test2 = z => 2 + addStuff(1)((() => {
+  if (z === 0) { return 5; }
+  const $0 = z - 1 | 0;
+  if ($0 === 0) { return 6; }
+  return 2 + addStuff($0 - 1 | 0)(5) | 0;
+})()) | 0;
+export {$List, Cons, Nil, addStuff, test1, test2};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
new file mode 100644
index 00000000..e9d90507
--- /dev/null
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
@@ -0,0 +1,17 @@
+-- @inline Snapshot.RecursionInlined02.addStuff always
+module Snapshot.RecursionInlined02 where
+
+import Prelude
+
+data List a = Nil | Cons a (List a)
+infixr 5 Cons as :
+
+addStuff :: Int -> Int -> Int
+addStuff x ys = if x == zero then ys else one + addStuff (x - one) ys
+
+infixr 4 addStuff as ++
+
+test1 :: Int
+test1 = 3 ++ 4
+test2 :: Int -> Int
+test2 z = 3 ++ z ++ 5
\ No newline at end of file
diff --git a/src/PureScript/Backend/Optimizer/Semantics.purs b/src/PureScript/Backend/Optimizer/Semantics.purs
index 133bc707..eb07f81a 100644
--- a/src/PureScript/Backend/Optimizer/Semantics.purs
+++ b/src/PureScript/Backend/Optimizer/Semantics.purs
@@ -193,6 +193,7 @@ recursable = go
   go arr
     | Just { head, tail } <- Array.uncons arr = case head of
         NeutData _ _ _ _ _ -> go tail
+        NeutLit _ -> go tail
         _ -> false
     | otherwise = true
 

From 1f61d1c2889f6a041c8b8a34cd01f75f81833014 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 12:16:09 +0300
Subject: [PATCH 10/14] Smarter function

---
 .../Snapshot.RecursionInlined02.js            | 22 ++++++++++++++-----
 .../Snapshot.RecursionInlined02.purs          |  5 ++++-
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
index 6a873805..64399cee 100644
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
@@ -3,14 +3,24 @@ const $List = (tag, _1, _2) => ({tag, _1, _2});
 const Nil = /* #__PURE__ */ $List("Nil");
 const Cons = value0 => value1 => $List("Cons", value0, value1);
 const addStuff = x => ys => {
-  if (x === 0) { return ys; }
-  return 1 + addStuff(x - 1 | 0)(ys) | 0;
+  if (x > 0) { return 1 + addStuff(x - 1 | 0)(ys) | 0; }
+  if (x < 0) { return -1 + addStuff(x + 1 | 0)(ys) | 0; }
+  return ys;
 };
 const test1 = 7;
 const test2 = z => 2 + addStuff(1)((() => {
-  if (z === 0) { return 5; }
-  const $0 = z - 1 | 0;
-  if ($0 === 0) { return 6; }
-  return 2 + addStuff($0 - 1 | 0)(5) | 0;
+  if (z > 0) {
+    const $0 = z - 1 | 0;
+    if ($0 > 0) { return 2 + addStuff($0 - 1 | 0)(5) | 0; }
+    if ($0 < 0) { return 0 + addStuff($0 + 1 | 0)(5) | 0; }
+    return 6;
+  }
+  if (z < 0) {
+    const $0 = z + 1 | 0;
+    if ($0 > 0) { return 0 + addStuff($0 - 1 | 0)(5) | 0; }
+    if ($0 < 0) { return -2 + addStuff($0 + 1 | 0)(5) | 0; }
+    return 4;
+  }
+  return 5;
 })()) | 0;
 export {$List, Cons, Nil, addStuff, test1, test2};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
index e9d90507..6703dc9e 100644
--- a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
@@ -7,7 +7,10 @@ data List a = Nil | Cons a (List a)
 infixr 5 Cons as :
 
 addStuff :: Int -> Int -> Int
-addStuff x ys = if x == zero then ys else one + addStuff (x - one) ys
+addStuff x ys
+  | x > 0 = 1 + addStuff (x - 1) ys
+  | x < 0 = (-1) + addStuff (x + 1) ys
+  | otherwise = ys
 
 infixr 4 addStuff as ++
 

From e3c89426dbb856b9bfe5b84178773f7e70485c5f Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 12:21:35 +0300
Subject: [PATCH 11/14] Adds test for non-terminating recursion

---
 .../Snapshot.RecursionInlinedBroken.js        | 17 +++++++++++++++++
 .../Snapshot.RecursionInlinedBroken.purs      | 19 +++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js
 create mode 100644 backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js
new file mode 100644
index 00000000..c4d23a39
--- /dev/null
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js
@@ -0,0 +1,17 @@
+// @inline Snapshot.RecursionInlinedBroken.addStuffBroken always
+// This will recurse out of control and stop when it hits the recursion limit
+const $List = (tag, _1, _2) => ({tag, _1, _2});
+const Nil = /* #__PURE__ */ $List("Nil");
+const Cons = value0 => value1 => $List("Cons", value0, value1);
+const addStuffBroken = v => v1 => {
+  if (v === 0) { return v1; }
+  return 1 + addStuffBroken(v - 1 | 0)(v1) | 0;
+};
+const test1 = /* #__PURE__ */ (() => 2 + addStuffBroken(-5)(4) | 0)();
+const test2 = z => 2 + addStuffBroken(-5)((() => {
+  if (z === 0) { return 5; }
+  const $0 = z - 1 | 0;
+  if ($0 === 0) { return 6; }
+  return 2 + addStuffBroken($0 - 1 | 0)(5) | 0;
+})()) | 0;
+export {$List, Cons, Nil, addStuffBroken, test1, test2};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs b/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs
new file mode 100644
index 00000000..1cb71e46
--- /dev/null
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs
@@ -0,0 +1,19 @@
+-- @inline Snapshot.RecursionInlinedBroken.addStuffBroken always
+-- This will recurse out of control and stop when it hits the recursion limit
+module Snapshot.RecursionInlinedBroken where
+
+import Prelude
+
+data List a = Nil | Cons a (List a)
+infixr 5 Cons as :
+
+addStuffBroken :: Int -> Int -> Int
+addStuffBroken 0 ys = ys
+addStuffBroken x ys = 1 + addStuffBroken (x - 1) ys
+
+infixr 4 addStuffBroken as ++
+
+test1 :: Int
+test1 = (-3) ++ 4
+test2 :: Int -> Int
+test2 z = (-3) ++ z ++ 5
\ No newline at end of file

From d92b4f19e55ad8d0537dddd871a5258b008d23d2 Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 13:28:32 +0300
Subject: [PATCH 12/14] Adds broken test

---
 .../test/snapshots-out/Snapshot.RecursionInlined02.js      | 2 +-
 .../test/snapshots-out/Snapshot.RecursionInlinedBroken.js  | 2 +-
 backend-es/test/snapshots/Snapshot.RecursionInlined02.purs | 2 +-
 .../test/snapshots/Snapshot.RecursionInlinedBroken.purs    | 7 +++++--
 4 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
index 64399cee..9c8a958e 100644
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined02.js
@@ -7,7 +7,7 @@ const addStuff = x => ys => {
   if (x < 0) { return -1 + addStuff(x + 1 | 0)(ys) | 0; }
   return ys;
 };
-const test1 = 7;
+const test1 = 42;
 const test2 = z => 2 + addStuff(1)((() => {
   if (z > 0) {
     const $0 = z - 1 | 0;
diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js
index c4d23a39..d3aabe35 100644
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlinedBroken.js
@@ -7,7 +7,7 @@ const addStuffBroken = v => v1 => {
   if (v === 0) { return v1; }
   return 1 + addStuffBroken(v - 1 | 0)(v1) | 0;
 };
-const test1 = /* #__PURE__ */ (() => 2 + addStuffBroken(-5)(4) | 0)();
+const test1 = v => 2 + addStuffBroken(-5)(4) | 0;
 const test2 = z => 2 + addStuffBroken(-5)((() => {
   if (z === 0) { return 5; }
   const $0 = z - 1 | 0;
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
index 6703dc9e..cb3425b0 100644
--- a/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined02.purs
@@ -15,6 +15,6 @@ addStuff x ys
 infixr 4 addStuff as ++
 
 test1 :: Int
-test1 = 3 ++ 4
+test1 = 38 ++ 4
 test2 :: Int -> Int
 test2 z = 3 ++ z ++ 5
\ No newline at end of file
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs b/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs
index 1cb71e46..9628c151 100644
--- a/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlinedBroken.purs
@@ -13,7 +13,10 @@ addStuffBroken x ys = 1 + addStuffBroken (x - 1) ys
 
 infixr 4 addStuffBroken as ++
 
-test1 :: Int
-test1 = (-3) ++ 4
+-- we make this Unit -> Int so that the module can be loaded with an
+-- import statement. otherwise, it will execute the broken (-3) ++ 4 and the
+-- tests will fail
+test1 :: Unit -> Int
+test1 _ = (-3) ++ 4
 test2 :: Int -> Int
 test2 z = (-3) ++ z ++ 5
\ No newline at end of file

From 0282279c0158e9dcd39116f9bb69ba87ef2c942f Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 13:39:47 +0300
Subject: [PATCH 13/14] Adds composition test

---
 .../snapshots-out/Snapshot.RecursionInlined03.js    |  6 ++++++
 .../test/snapshots/Snapshot.RecursionInlined03.purs | 13 +++++++++++++
 2 files changed, 19 insertions(+)
 create mode 100644 backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js
 create mode 100644 backend-es/test/snapshots/Snapshot.RecursionInlined03.purs

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js
new file mode 100644
index 00000000..2fe576f0
--- /dev/null
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js
@@ -0,0 +1,6 @@
+// @inline Snapshot.RecursionInlined03.compose always
+const id = a => a;
+const compose = ab => bc => a => bc(ab(a));
+const test1 = a => a;
+const test2 = z => a => z(a);
+export {compose, id, test1, test2};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs
new file mode 100644
index 00000000..ad98ead8
--- /dev/null
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs
@@ -0,0 +1,13 @@
+-- @inline Snapshot.RecursionInlined03.compose always
+module Snapshot.RecursionInlined03 where
+
+compose :: forall a b c. (a -> b) -> (b -> c) -> (a -> c)
+compose ab bc a = bc (ab a)
+
+id :: forall a. a -> a
+id a = a
+
+test1 :: Int -> Int
+test1 =compose id (compose id (compose id (compose id id)))
+test2 :: (Int -> Int) -> Int -> Int
+test2 z = compose id (compose id (compose z (compose id id)))
\ No newline at end of file

From a93cd811f6651e4be1a8c19f709df125e21bde4f Mon Sep 17 00:00:00 2001
From: Mike Solomon <mike@meeshkan.com>
Date: Mon, 26 Jun 2023 15:12:43 +0300
Subject: [PATCH 14/14] Adds test that does not work yet for variants

---
 .../Snapshot.RecursionInlined03.js            | 54 ++++++++++++++++---
 .../Snapshot.RecursionInlined03.purs          | 36 +++++++++----
 2 files changed, 75 insertions(+), 15 deletions(-)

diff --git a/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js b/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js
index 2fe576f0..97adba14 100644
--- a/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js
+++ b/backend-es/test/snapshots-out/Snapshot.RecursionInlined03.js
@@ -1,6 +1,48 @@
-// @inline Snapshot.RecursionInlined03.compose always
-const id = a => a;
-const compose = ab => bc => a => bc(ab(a));
-const test1 = a => a;
-const test2 = z => a => z(a);
-export {compose, id, test1, test2};
+// @inline Snapshot.RecursionInlined03.append always
+// This doesn't quite work yet, because the inlining of append depends
+// on the analysis of the local `b`, which we don't have (easy) access to.
+// If we can somehow grab its usage, we'd likely see that access + case == total
+import * as Partial from "../Partial/index.js";
+const List = x => x;
+const nil = {type: "nil", value: undefined};
+const cons = head => tail => ({type: "cons", value: {head, tail}});
+const append = v => b => {
+  if (v.type === "cons") { return {type: "cons", value: {head: v.value.head, tail: append(v.value.tail)(b)}}; }
+  if (v.type === "nil") { return b; }
+  return Partial._crashWith("Data.Variant: pattern match failure [" + v.type + "]");
+};
+const test1 = {
+  type: "cons",
+  value: {
+    head: "a",
+    tail: {
+      type: "cons",
+      value: {
+        head: "b",
+        tail: /* #__PURE__ */ append({type: "cons", value: {head: "c", tail: nil}})({
+          type: "cons",
+          value: {head: "d", tail: {type: "cons", value: {head: "e", tail: {type: "cons", value: {head: "f", tail: {type: "cons", value: {head: "g", tail: nil}}}}}}}
+        })
+      }
+    }
+  }
+};
+const test2 = z => (
+  {
+    type: "cons",
+    value: {
+      head: "a",
+      tail: {
+        type: "cons",
+        value: {
+          head: "b",
+          tail: append({type: "cons", value: {head: "c", tail: z}})({
+            type: "cons",
+            value: {head: "d", tail: {type: "cons", value: {head: "e", tail: {type: "cons", value: {head: "f", tail: {type: "cons", value: {head: "g", tail: nil}}}}}}}
+          })
+        }
+      }
+    }
+  }
+);
+export {List, append, cons, nil, test1, test2};
diff --git a/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs b/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs
index ad98ead8..aefd068a 100644
--- a/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs
+++ b/backend-es/test/snapshots/Snapshot.RecursionInlined03.purs
@@ -1,13 +1,31 @@
--- @inline Snapshot.RecursionInlined03.compose always
+-- @inline Snapshot.RecursionInlined03.append always
+-- This doesn't quite work yet, because the inlining of append depends
+-- on the analysis of the local `b`, which we don't have (easy) access to.
+-- If we can somehow grab its usage, we'd likely see that access + case == total
 module Snapshot.RecursionInlined03 where
 
-compose :: forall a b c. (a -> b) -> (b -> c) -> (a -> c)
-compose ab bc a = bc (ab a)
+import Prelude
 
-id :: forall a. a -> a
-id a = a
+import Data.Variant (Variant, inj, case_, on)
+import Type.Proxy (Proxy(..))
 
-test1 :: Int -> Int
-test1 =compose id (compose id (compose id (compose id id)))
-test2 :: (Int -> Int) -> Int -> Int
-test2 z = compose id (compose id (compose z (compose id id)))
\ No newline at end of file
+newtype List a = List (Variant (nil :: Unit, cons :: { head :: a, tail :: List a }))
+
+cons :: forall a. a -> List a -> List a
+cons head tail = List $ inj (Proxy :: _ "cons") {head, tail}
+nil :: forall a. List a
+nil = List $ inj (Proxy :: _ "nil") unit
+infixr 5 cons as :
+
+append :: forall a. List a -> List a -> List a
+append (List a) b = (case_
+  # on (Proxy :: _ "nil") (\_ -> b)
+  # on (Proxy :: _ "cons") (\{head, tail} -> cons head (append tail b))) a
+
+infixr 4 append as <>
+
+test1 :: List String
+test1 = ("a" : "b" : "c" : nil) <> ("d" : "e" : "f" : "g" : nil)
+
+test2 :: List String -> List String
+test2 z = ("a" : "b" : "c" : z) <> ("d" : "e" : "f" : "g" : nil)
\ No newline at end of file