[iter] Add hb_chop()

src/hb-iter.hh

@@ -748,6 +748,7 @@ struct
   ( hb_zip (hb_iota (start), it) )
 }
 HB_FUNCOBJ (hb_enumerate);
+
 struct
 { HB_PARTIALIZE(2);
   template <typename Iterable,
@@ -767,6 +768,19 @@ struct
 }
 HB_FUNCOBJ (hb_take);
 
+struct
+{ HB_PARTIALIZE(2);
+  template <typename Iter,
+	    hb_requires (hb_is_iterator (Iter))>
+  auto operator () (Iter it, unsigned count) const HB_AUTO_RETURN
+  (
+    + hb_iota (it, hb_partial<2> (hb_add, count))
+    | hb_map (hb_partial<2> (hb_take, count))
+    | hb_take ((hb_len (it) + count - 1) / count)
+  )
+}
+HB_FUNCOBJ (hb_chop);
+
 /* hb_sink() */
 
 template <typename Sink>

src/test-iter.cc

@@ -271,7 +271,7 @@ main (int argc, char **argv)
   hb_range ();
   hb_repeat (7u);
   hb_repeat (nullptr);
-  hb_repeat (vl);
+  hb_repeat (vl) | hb_chop (3);
   assert (hb_len (hb_range (10) | hb_take (3)) == 3);
   assert (hb_range (9).len () == 9);
   assert (hb_range (2, 9).len () == 7);