Minimal Seq.AT-POS attempt

gistfile1.txt

diff --git a/src/core.c/Seq.pm6 b/src/core.c/Seq.pm6
index 8b06b1628..f9d5f1643 100644
--- a/src/core.c/Seq.pm6
+++ b/src/core.c/Seq.pm6
@@ -5,6 +5,9 @@ my class Seq is Cool does Iterable does Sequence {
     # way through. Can only be obtained once.
     has Iterator $!iter;
 
+    # The number of values that have been produced
+    has int $!produced;
+
     # The only valid way to create a Seq directly is by giving it the
     # iterator it will consume and maybe memoize.
     multi method new(Seq: Iterator:D $iter) {
@@ -41,6 +44,20 @@ my class Seq is Cool does Iterable does Sequence {
         )
     }
 
+    proto method AT-POS(|) {*}
+    multi method AT-POS(int $pos) is raw {
+        if $pos < $!produced {
+            die "asked $pos, which was already produced";
+        }
+        else {
+            my int $skip = $pos - $!produced;
+            $!produced = $pos;
+            $!iter.skip($skip)
+              ?? $!iter.pull-one
+              !! Nil
+        }
+    }
+
     multi method Seq(Seq:D:)   { self }
 
     method Capture() {