my take on infix:<,>(a,b) so far

gistfile1.txt

diff --git a/src/core/List.pm b/src/core/List.pm
index 8bd7c66..21086ed 100644
--- a/src/core/List.pm
+++ b/src/core/List.pm
@@ -1443,41 +1443,39 @@ my class List does Iterable does Positional { # declared in BOOTSTRAP
 # The , operator produces a List.
 proto sub infix:<,>(|) is pure {*}
 multi sub infix:<,>() { nqp::create(List) }
-multi sub infix:<,>(|) {
-
-    # look for a Slip in the parameters
-    my \in := nqp::p6argvmarray();
-    my int $i     = -1;
-    my int $elems = nqp::elems(in);
-    nqp::while(
-      (nqp::islt_i(($i = nqp::add_i($i,1)),$elems)
-        && nqp::not_i(nqp::istype(nqp::atpos(in,$i),Slip))),
-      nqp::null
-    );
-
+multi sub infix:<,>(\a) {
+    nqp::if(
+      nqp::istype(a,Slip),
+      Rakudo::Internals.UPGRADE-LIST-WITH-SLIP(nqp::p6argvmarray,0),
+      nqp::p6bindattrinvres(nqp::create(List),List,'$!reified',nqp::p6argvmarray)
+    )
+}
+multi sub infix:<,>(\a,\b) {
     nqp::if(
-      nqp::iseq_i($i,$elems),  # no Slip seen, so just alias input params
-      nqp::p6bindattrinvres(nqp::create(List),List,'$!reified',in),
-      nqp::stmts(  # Slip seen, first copy non-slippy things
-        ($elems = $i),
-        ($i     = -1),
-        (my $reified := nqp::setelems(nqp::create(IterationBuffer),$elems)),
-        nqp::while(
-          nqp::islt_i(($i = nqp::add_i($i,1)),$elems),
-          nqp::bindpos($reified,$i,nqp::shift(in))
-        ),
-        # now set up the List with a future
-        (my $list :=
-          nqp::p6bindattrinvres(nqp::create(List),List,'$!reified',$reified)),
-        nqp::bindattr($list,List,'$!todo',
-          my $todo:= nqp::create(List::Reifier)),
-        nqp::bindattr($todo,List::Reifier,'$!reified',$reified),
-        nqp::bindattr($todo,List::Reifier,'$!future',in),
-        nqp::bindattr($todo,List::Reifier,'$!reification-target',$reified),
-        $list
+      nqp::istype(a,Slip),
+      Rakudo::Internals.UPGRADE-LIST-WITH-SLIP(nqp::p6argvmarray,0),
+      nqp::if(
+        nqp::istype(b,Slip),
+        Rakudo::Internals.UPGRADE-LIST-WITH-SLIP(nqp::p6argvmarray,1),
+        nqp::p6bindattrinvres(nqp::create(List),List,'$!reified',nqp::p6argvmarray)
       )
     )
 }
+multi sub infix:<,>(|) {
+    nqp::stmts(
+      (my \in := nqp::p6argvmarray),
+      (my int $elems = nqp::elems(in)),
+      (my int $i = -1),
+      nqp::while(                                # look for Slip in parameters
+        nqp::islt_i(($i = nqp::add_i($i,1)),$elems),
+        nqp::if(
+          nqp::istype(nqp::atpos(in,$i),Slip),   # found a Slip, use slow-path
+          (return Rakudo::Internals.UPGRADE-LIST-WITH-SLIP(in,$i))
+        )
+      ),
+      nqp::p6bindattrinvres(nqp::create(List),List,'$!reified',in)
+    )
+}
 
 sub combinations(Int() $n, Int() $k) {
     Seq.new(Rakudo::Iterator.Combinations($n,$k,0))
diff --git a/src/core/Rakudo/Internals.pm b/src/core/Rakudo/Internals.pm
index 5e5f940..5957775 100644
--- a/src/core/Rakudo/Internals.pm
+++ b/src/core/Rakudo/Internals.pm
@@ -2,6 +2,7 @@ my class DateTime { ... }
 my role  IO { ... }
 my class IO::Handle { ... }
 my class IO::Path { ... }
+my class List::Reifier { ... }
 my class Rakudo::Metaops { ... }
 
 my class X::Assignment::ToShaped { ... }
@@ -208,6 +209,27 @@ my class Rakudo::Internals {
         )
     }
 
+    # Upgrade the given (auto-HLLized) List with an p6argvmarray to a proper
+    # List with a reified and a todo part, and return the given List.
+    method UPGRADE-LIST-WITH-SLIP(List:D $list, int $from --> List:D) {
+        nqp::stmts(
+          (my \in := nqp::getattr($list,List,'$!reified')),
+          # reuse autogenned List object
+          nqp::bindattr($list,List,'$!reified',my $reified := nqp::list),
+          (my int $i = -1),
+          nqp::while(                            # copy already reified stuff
+            nqp::islt_i(($i = nqp::add_i($i,1)),$from),
+            nqp::push($reified,nqp::shift(in))
+          ),
+          # now set up the List with a future
+          nqp::bindattr($list,List,'$!todo',my $todo:= nqp::create(List::Reifier)),
+          nqp::bindattr($todo,List::Reifier,'$!reified',$reified),
+          nqp::bindattr($todo,List::Reifier,'$!future',in),
+          nqp::bindattr($todo,List::Reifier,'$!reification-target',$reified),
+          $list
+        )
+    }
+
     # fast whitespace trim: str to trim, str to store trimmed str
     method TRIM(\string, \trimmed --> Nil) {
         my int $pos  = nqp::chars(string) - 1;