Volume of mesh

Calculates the volume of a point-face triangel mesh. 
points=[[0,0,0], ... ]
faces=[[0,1,2],[0,2,3],[4,6,5],[4,7,6],
    [0,4,5],[1,0,5],[1,5,6],[2,1,6],
    [2,6,7],[2,7,3],[3,7,4],[3,0,4]]    
function    meshVolume(points,faces)=
   let(
 
    sum=[for(faces)-1]*[for(f=faces)
SignedVolumeOfTriangle(points[f[0]],points[f[1]],points[f[2]])])
    sum
    
    
    
    
    ;
    
    
   function SignedVolumeOfTriangle(  p1,   p2,   p3) =
    let(
     v321 = p3.x*p2.y*p1.z,
     v231 = p2.x*p3.y*p1.z,
     v312 = p3.x*p1.y*p2.z,
     v132 = p1.x*p3.y*p2.z,
     v213 = p2.x*p1.y*p3.z,
     v123 = p1.x*p2.y*p3.z
)     (1.0/6.0)*(-v321 + v231 + v312 - v132 - v213 + v123);