Trap succeed in blocks that signature-bind $_

src/NAMOutput.pm6

@@ -16,7 +16,11 @@ method run($*unit) {
 }
 
 sub nam_sub($s) {
-    @*subsnam[$s.xref[1]] = $s.code.cgop($s);
+    my $code = $s.code;
+    if $s.topicalizer {
+        $code = ::Op::TopicalHook.new(inner => $code);
+    }
+    @*subsnam[$s.xref[1]] = $code.cgop($s);
     if $s.parametric_role_hack {
         for @( $*unit.deref($s.parametric_role_hack).methods ) -> $me {
             if $me.name ~~ ::GLOBAL::Op {

src/NieczaPassBeta.pm6

@@ -106,5 +106,9 @@ sub beta_optimize($body, $op, $inv, $cbody) {
         $nop = ::Op::Let.new(var => $a.[1], to => $a.[0], in => $nop);
     }
 
+    if $cbody.topicalizer {
+        $nop = ::Op::TopicalHook.new(inner => $nop);
+    }
+
     $nop;
 }

src/niecza

@@ -18,6 +18,7 @@ use MONKEY_TYPING;
 
 use NieczaActions;
 use Operator;
+use CgOp;
 sub node($M) { { line => $M.cursor.lineof($M.to) } }
 
 sub mklet($value, $body) {
@@ -38,6 +39,27 @@ augment class NieczaActions {
     method infix:sym<~~> ($/) { make ::Operator::SmartMatch.new }
 }
 
+augment class Metamodel::StaticSub { #OK exist
+    method topicalizer() {
+        $.signature && ?( grep { .slot && .slot eq '$_' }, @( $.signature.params ) )
+    }
+}
+
+augment class Op {
+class TopicalHook is Op {
+    has $.inner;
+    method zyg() { $.inner }
+
+    method code($body) {
+        my $id = ::GLOBAL::NieczaActions.genid;
+
+        CgOp.prog(
+            CgOp.ehspan(6, '', 0, "start$id", "end$id", "end$id"),
+            CgOp.span("start$id", "end$id", 0, $.inner.cgop($body)));
+    }
+}
+}
+
 augment class Operator {
 class SmartMatch is Operator {
     method as_function($/) { mklex($/, '&infix:<~~>') }