Well, the direct equivalent* of mine, above, would be:
(* other than scoping issues of $i)

  my $i = 0;
  while ( $i <= $#a ) {
      push @b, [ @a[ $i .. $i+$n-1 ] ];
  }
  continue {
      $i += $n;
  }
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Thing I don't like about yours is the incessant multiplication by $n.