\useMPlibrary[txt]

\startuseMPgraphic{shape}
  % Shape of the paragraph
  path p ; p := ((0,1)..(-1,0)..(1,0)--cycle) scaled 5cm ;
 
  
  build_parshape
  ( p,                     % shape path
   .5*\baselinedistance,  % offset
   .5*\baselinedistance,  % x offset
   .5*\baselinedistance,  % y offset
   \baselinedistance,     % distance between lines
   \strutheight,          % height of a line
   \strutdepth,           % depth of a line
   \strutheight           % height of the first line
  ) ;

% For visualization purposes only
  draw p;
 \stopuseMPgraphic

% For visualization purposes only
\defineoverlay[shape][\useMPgraphic{shape}]

\setupshapetexts%
  [bodyfont=10pt]

\starttext
\startshapetext[shape]
  \input knuth \endgraf
\stopshapetext


% The \type{background} is set only to visualize the parshape
\startTEXpage[background=shape,offset=2mm]
{\getshapetext}
\stopTEXpage
\stoptext