Is there a different approach to use boxes.mp?

MNWE:

\startMPpage
input boxes.mp;
  boxit.bl("left");
  boxit.br("right");
  br.sw - bl.ne = (20,0);
  drawboxed(bl,br);
\stopMPpage

LOG snippets:

system          > ConTeXt  ver: 2020.04.10 19:11 MKIV beta  fmt: 2020.4.19  int: english/english

metapost log    > loading metafun, including plain.mp version 1.004 for metafun iv and xl
metapost log    > 
metapost log    > >> _dojoin
metapost log    > ! Isolated expression.