sanity check parameters List.rotor

gistfile1.txt

diff --git a/src/core/List.pm b/src/core/List.pm
index 17bf04b..5d3cc5f 100644
--- a/src/core/List.pm
+++ b/src/core/List.pm
@@ -563,15 +563,23 @@ my class List does Positional { # declared in BOOTSTRAP
     }
 
     method rotor(*@cycle, :$partial) {
-        my $finished = 0;
+
+        die "Must specify at least one pattern of cyclism" unless @cycle;
+
         # (Note, the xx should be harmless if the cycle is already infinite by accident.)
         my @c := @cycle.infinite ?? @cycle !! @cycle xx *;
+        my $finished = 0;
         gather for @c -> $s {
             my $elems;
             my $gap;
             if $s ~~ Pair { $elems = +$s.key; $gap = +$s.value; }
             else          { $elems = +$s;     $gap = 0; }
 
+            fail X::OutOfRange.new(:what<Elements>,:got($elems),:range<1..Inf>)
+              if $elems < 1;
+            fail X::OutOfRange.new(:what<Start>,:got($finished),:range(0..Inf))
+              if $finished < 0;
+
             if $finished + $elems <= self.gimme($finished + $elems) {
                 take self[$finished ..^ $finished + $elems];
                 $finished += $elems + $gap;

gistfile2.txt

$ 6 '{ (^10).rotor(-1 => 1) }' | pbcopy
Unhandled exception: Could not find symbol '&Return'
   at src/gen/m-CORE.setting:14576  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:throw:121)
 from src/gen/m-CORE.setting:16449  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:<anon>:33)
 from src/gen/m-Metamodel.nqp:2914  (blib/Perl6/Metamodel.moarvm:find_method_fallback:69)
 from src/gen/m-Metamodel.nqp:1053  (blib/Perl6/Metamodel.moarvm:find_method:110)
 from src/gen/m-BOOTSTRAP.nqp:2732  (blib/Perl6/BOOTSTRAP.moarvm::85)
 from src/gen/m-CORE.setting:889  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:EXHAUST:32)
 from src/gen/m-CORE.setting:16462  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:fail:36)
 from src/gen/m-CORE.setting:16458  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:fail:25)
 from src/gen/m-CORE.setting:10813  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::133)
 from src/gen/m-CORE.setting:10036  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::558)
 from src/gen/m-CORE.setting:9959  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:reify:58)
 from src/gen/m-CORE.setting:9875  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::95)
 from src/gen/m-CORE.setting:9846  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::0)
 from src/gen/m-CORE.setting:9846  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:reify:58)
 from src/gen/m-CORE.setting:10372  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:gimme:4294967295)
 from src/gen/m-CORE.setting:10914  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:sink:4294967295)
 from src/gen/m-CORE.setting:10807  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::31)
 from src/gen/m-CORE.setting:10179  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::18)
 from src/gen/m-CORE.setting:10183  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::10)
 from src/gen/m-CORE.setting:10210  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::48)
 from src/gen/m-CORE.setting:10203  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:reify:52)
 from src/gen/m-CORE.setting:9875  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::95)
 from src/gen/m-CORE.setting:9846  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm::0)
 from src/gen/m-CORE.setting:9846  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:reify:58)
 from src/gen/m-CORE.setting:10372  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:gimme:4294967295)
 from src/gen/m-CORE.setting:10914  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/./CORE.setting.moarvm:sink:4294967295)
 from src/gen/m-main.nqp:41  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/perl6.moarvm:MAIN:40)
 from src/gen/m-main.nqp:35  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/perl6.moarvm:<mainline>:197)
 from <unknown>:1  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/perl6.moarvm:<main>:8)
 from <unknown>:1  (/Users/liz/Github/rakudo.moar/install/share/perl6/runtime/perl6.moarvm:<entry>:9)