Error found:
in module Main
at tests/purs/failing/3510.purs:7:1 - 7:28 (line 7, column 1 - line 7, column 28)

  Type class instance head is invalid due to use of type
      
    ()
      
  All types appearing in instance declarations must be of the form T a_1 .. a_n, where each type a_i is of the same form, unless the type is fully determined by other type class arguments via functional dependencies.

in type class instance
              
  Data.Eq.Eq T
              

See https://github.com/purescript/documentation/blob/master/errors/InvalidInstanceHead.md for more information,
or to contribute content related to this error.