towards @_ support and increasing seqs by default

if the arity of the code for the limit is 0 and the count
is Inf, I try to pass all values so far into the code.

in addition, lists that start with a single number and then
have a limit block will now be increasing, rather than
decreasing (strange to have ... * be increasing and ... * > 5
be decreasing instead)

src/core/operators.pm

@@ -86,9 +86,13 @@ sub SEQUENCE($left, Mu $right, :$exclude_end) {
     my $infinite = $endpoint ~~ Whatever || $endpoint === $Inf;
     $endpoint = Bool::False if $infinite;
     my $tail := ().list;
-    my int $end_code_arity = -1;
+    my $end_code_arity = 0;
     my $end_tail := ().list;
-    $end_code_arity = $endpoint.arity if $endpoint ~~ Code;
+    if $endpoint ~~ Code {
+        $end_code_arity = $endpoint.arity;
+        $end_code_arity = $endpoint.count if $end_code_arity == 0;
+        $end_code_arity = -Inf if $end_code_arity ~~ Inf;
+    }
 
     my sub succpred($cmp) {
         ($cmp < 0) ?? { $^x.succ } !! ( $cmp > 0 ?? { $^x.pred } !! { $^x } )
@@ -105,10 +109,10 @@ sub SEQUENCE($left, Mu $right, :$exclude_end) {
         while @left {
             $value = @left.shift;
             if $value ~~ Code { $code = $value; last }
-            if $end_code_arity > 1 {
+            if $end_code_arity != 0 {
                 $end_tail.push($value);
                 if +@$end_tail >= $end_code_arity {
-                    $end_tail.munch($end_tail.elems - $end_code_arity);
+                    $end_tail.munch($end_tail.elems - $end_code_arity) unless $end_code_arity ~~ -Inf;
                     if $endpoint(|@$end_tail) { $stop = 1; last }
                 }
             } elsif $value ~~ $endpoint  { $stop = 1; last }
@@ -165,7 +169,7 @@ sub SEQUENCE($left, Mu $right, :$exclude_end) {
                 }
             }
             elsif $tail.elems == 1 {
-                $code = $a cmp $endpoint > 0 ?? { $^x.pred } !! { $^x.succ }
+                $code = ($a cmp $endpoint > 0 || $endpoint ~~ Code)?? { $^x.pred } !! { $^x.succ }
             }
             elsif $tail.elems == 0 {
                 $code = {()}
@@ -176,10 +180,10 @@ sub SEQUENCE($left, Mu $right, :$exclude_end) {
                 while 1 {
                     $tail.munch($tail.elems - $count);
                     $value := $code(|$tail);
-                    if $end_code_arity > 1 {
+                    if $end_code_arity != 0 {
                         $end_tail.push($value);
                         unless $end_tail.elems < $end_code_arity {
-                            $end_tail.munch($end_tail.elems - $end_code_arity);
+                            $end_tail.munch($end_tail.elems - $end_code_arity) unless $end_code_arity ~~ -Inf;
                             last if $endpoint(|@$end_tail);
                         }
                     } else {