Error found:
at tests/purs/failing/ExtraneousClassMember.purs:11:3 - 11:10 (line 11, column 3 - line 11, column 10)

  b is not a member of type class Main.A

in type class instance
               
  Main.A String
               

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