t3015.scala:7: error: scrutinee is incompatible with pattern type;
 found   : _$1 where type _$1
 required: String
  val b(foo) = "foo" 
       ^
t3015.scala:7: error: type mismatch;
 found   : _$1(in value foo) where type _$1(in value foo) <: String
 required: (some other)_$1(in value foo) where type (some other)_$1(in value foo)
  val b(foo) = "foo" 
      ^
two errors found