Refactor METAOP_ASSIGN_NEW

It now takes the name and the op, making things simpler and allows it to
also be used for priming.

src/core/metaops.pm6

@@ -1,25 +1,25 @@
 
 my $METAOP_ASSIGN := nqp::hash;
+sub METAOP_ASSIGN_NEW(\name, \op) {
+    nqp::if(
+      name,
+      nqp::stmts(
+        nqp::bindkey($METAOP_ASSIGN,name,op),
+        op.set_name(name.substr(0,*-1) ~ "=>"),
+      )
+    );
+    op
+}
+
 sub METAOP_ASSIGN(\op) {
     nqp::ifnull(
       nqp::atkey($METAOP_ASSIGN,op.name),
-      METAOP_ASSIGN_NEW(op)
+      METAOP_ASSIGN_NEW(
+        op.name,
+        -> Mu \a, Mu \b { a = op.((a.DEFINITE ?? a !! op.()), b) }
+      )
     )
 }
-sub METAOP_ASSIGN_NEW(\op) {
-    # Fast path the case where there is *no* name for the op.  If we *do* have
-    # a name, then we'll only be here once for that op, so it doesn't matter
-    # that we call op.name multiple times.
-    op.name
-      ?? nqp::bindkey($METAOP_ASSIGN,op.name,nqp::stmts(
-           (my \metaop :=
-             -> Mu \a, Mu \b { a = op.((a.DEFINITE ?? a !! op.()), b) }
-           ),
-           metaop.set_name(op.name.substr(0,*-1) ~ "=>"),
-           metaop
-         ))
-      !! -> Mu \a, Mu \b { a = op.((a.DEFINITE ?? a !! op.()), b) }
-}
 
 sub METAOP_TEST_ASSIGN:<//>(\lhs, $rhs) is raw { lhs // (lhs = $rhs()) }
 sub METAOP_TEST_ASSIGN:<||>(\lhs, $rhs) is raw { lhs || (lhs = $rhs()) }