Initial version of Seq.sort . Seems to have issues with

arity-1 blocks; working on those a bit more.

src/core/Seq.pm

@@ -4,6 +4,36 @@ augment class Seq {
     method Str() {
         pir::join(' ', self!fill);
     }
+
+    multi method sort(&by = pir::get_hll_global__Ps('&infix:<cmp>')) {
+        # Parrot already provides a sort method that works on
+        # ResizablePMCArray, so we aim to make use of that here.
+        # Instead of sorting the elements directly, we sort an RPA
+        # of indices, then use that RPA as a slice into self.
+
+        # If &by.arity < 2, then it represents a block to be applied
+        # to the elements to obtain the values for sorting.
+        my ($list, &cmp);
+        if (&by.?arity // 2) < 2 {
+            $list = self.map(&by);
+            &cmp  = pir::get_hll_global__Ps('&infix:<cmp>');
+        }
+        else {
+            $list = self.eager;
+            &cmp = &by;
+        }
+
+        # Now we sort the list.  We create a RPA (Parcel) list of
+        # indices from 0 to $list.elems - 1, sort those using
+        # RPA.sort and &cmp, and slice the result.  (If &cmp
+        # indicates two elements are equal, we use the indices
+        # for the comparison, producing a stable sort.)
+        self[
+            (^pir::elements($list)).eager.sort( 
+                -> $a, $b { &cmp($list[$a], $list[$b]) || $a <=> $b }
+            )
+        ];
+    }
 }
 
 # vim: ft=perl6