The parens around elements in the list are not needed, e.g. [(a + b), 5] can be just [a + b, 5].

Instead of
v0
| x == 0 || x == 1 || x == 2 || x == 3 = -1
| x == 4 || x == 5 || x == 6 || x == 7 = 1
you may use
v0
| x `elem` [0,1,2,3] = -1
|otherwise = 1
Or use real arrays instead of the v function.
In fact I would directly put the values in the faces, without the v function or an array.

Also, in faces, don’t use nest lists but [(Float,Float,Float,Float)] to ensure the elements have each 4 values.

You can combine the zip and the mapM into zipWithM, or even better, zipWithM_, to avoid the need for return ().

Oh and slightly better name, in v x, v i would make in clear it is some kind of indexing, and using x, y, z instead of v1, v2, v3, make it clear these are 3d coord.

Alejandro.-