Implement .tail(*-N) for all but first N elements

rakudo · Apr 8, 2017 · 188b7b1 · 188b7b1
1 parent d673ea7
commit 188b7b1
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Showing 3 changed files with 25 additions and 7 deletions.
diff --git a/src/core/Any-iterable-methods.pm b/src/core/Any-iterable-methods.pm
@@ -1878,7 +1878,15 @@ Did you mean to add a stub (\{...\}) or did you mean to .classify?"
     }
     multi method tail(Any:D: $n) {
         Seq.new(
-          Rakudo::Iterator.LastNValues(self.iterator,$n,'tail')
+          nqp::if(
+            nqp::istype($n,Callable)
+              && nqp::isgt_i((my $skip := -($n(0).Int)),0),
+            nqp::stmts(
+              (my $iterator := self.iterator).skip-at-least($skip),
+              $iterator
+            ),
+            Rakudo::Iterator.LastNValues(self.iterator,$n,'tail')
+          )
         )
     }
 

diff --git a/src/core/Array.pm b/src/core/Array.pm
@@ -1050,9 +1050,14 @@ my class Array { # declared in BOOTSTRAP
                 && nqp::elems($reified),
               nqp::stmts(
                 (my $iterator := Rakudo::Iterator.ReifiedArray(self)),
-                nqp::unless(
-                  nqp::istype($n,Whatever) || $n == Inf,
-                  $iterator.skip-at-least(nqp::elems($reified) - $n)
+                nqp::if(
+                  nqp::istype($n,Callable)
+                    && nqp::isgt_i((my $skip := -($n(0).Int)),0),
+                  $iterator.skip-at-least($skip),
+                  nqp::unless(
+                    nqp::istype($n,Whatever) || $n == Inf,
+                    $iterator.skip-at-least(nqp::elems($reified) - $n)
+                  )
                 ),
                 $iterator
               ),

diff --git a/src/core/List.pm b/src/core/List.pm
@@ -1285,9 +1285,14 @@ my class List does Iterable does Positional { # declared in BOOTSTRAP
               $!reified.DEFINITE && nqp::elems($!reified),
               nqp::stmts(
                 (my $iterator := Rakudo::Iterator.ReifiedList(self)),
-                nqp::unless(
-                  nqp::istype($n,Whatever) || $n == Inf,
-                  $iterator.skip-at-least(nqp::elems($!reified) - $n)
+                nqp::if(
+                  nqp::istype($n,Callable)
+                    && nqp::isgt_i((my $skip := -($n(0).Int)),0),
+                  $iterator.skip-at-least($skip),
+                  nqp::unless(
+                    nqp::istype($n,Whatever) || $n == Inf,
+                    $iterator.skip-at-least(nqp::elems($!reified) - $n)
+                  )
                 ),
                 $iterator
               ),