Error found:
in module Main
at tests/purs/failing/Superclasses5.purs:17:1 - 18:18 (line 17, column 1 - line 18, column 18)

  A case expression could not be determined to cover all inputs.
  The following additional cases are required to cover all inputs:

    _

  Alternatively, add a Partial constraint to the type of the enclosing value.

while applying a function $__unused
  of type Partial => t1 -> t1
  to argument case $0 of       
                [ x ] -> [ su x
                         ]     
while checking that expression $__unused (case $0 of      
                                            [ x ] -> [ ...
                                                     ]    
                                         )                
  has type Array a0
in value declaration suArray

where a0 is a rigid type variable
        bound at (line 0, column 0 - line 0, column 0)
      t1 is an unknown type

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