grep.patch

--- c/src/core/Any.pm
+++ w/src/core/Any.pm
@@ -256,7 +256,21 @@ my class Any { # declared in BOOTSTRAP
         self.map({ next unless .match($test); $_ });
     }
     multi method grep(Callable:D $test) is rw {
-        self.map({ next unless $test($_); $_ });
+        if ($test.count == 1) {
+            self.map({next unless $test($_); $_});
+        } else {
+            my role CheatArity[$a,$c] {
+                has $.arity = $a;
+                has $.count = $c;
+            }
+
+            my &tester = -> |c {
+                next unless $test(|c);
+                c.list
+            } but CheatArity[$test.arity, $test.count];
+
+            self.map(&tester);
+        }
     }
     multi method grep(Mu $test) is rw {
         self.map({ next unless $_ ~~ $test; $_ });